Most popular discussions of antioxidants are based on an outdated view of free radicals as evil, toxic compounds, ones which cause chain reactions of destructive damage culminating in degenerative diseases and aging. Research in recent years has revealed that, in addition to cellular energy production, radicals play a crucial roles in many important physiological processes, including signal transduction, cell-cycle regulation, and immune function. Long-lived organisms, like humans, have developed very sophisticated enzymatic systems for controlling and utilizing radicals. These natural antioxidant defenses are much more effective than crude antioxidant supplements which have not been shown to be effective at preventing aging, or any degenerative disease. Some clinical trials of antioxidant supplementation have even found harmful effects. A number of such trials have been prematurely terminated for this reason. In fact, to date, despite decades of intense research, and thousands of studies, with extremely few exceptions, like radiation sickness, conclusive evidence has not been found that radical formation is a causative factor in the pathogenesis of diseases.
On the contrary, evidence indicates that, in most cases, radical formation results from, but does not cause disease processes.(ref, ref) Radical formation results from tissue injury, and is a necessary step in healing processes.(ref) As discussed in references cited below, radicals play a crucial role in developmental, metabolic, immunological, and other physiological functions. Without them we would not be able to produce energy, develop properly, repair injury; nor would we be able to destroy pathogens or infected and malignant cells. In rare cases, radicals may cause DNA damage possibly leading to cancer; however, on a regular, widespread basis, radicals are involved in the destruction of malignant cells, protecting us from cancer.
What are Free Radicals?
In general, the reactivity of an atom is determined by the electrons that have the most energy and move farthest from the nucleus. Pairs of electrons also tend to be more stable than single, unpaired electrons. Molecules that have unpaired electrons in their outer, valence shells are called “free radicals”. They may have an electrical charge, ions; but most are neutral. Molecules that give up, or “donate” an electron are said to be “oxidized”; while molecules that accept the electron are “reduced”. Such reduction-oxidation processes are called “redox” reactions. These reactions are essential to cellular energy production, and play a vital role in very important biological signaling pathways. Antioxidants are reducing agents. They can decrease oxidative damage, but can also interfere with vital biological processes. Maintenance of redox homeostasis (a balanced level of oxidative radicals) is necessary for proper cellular function.
ROS, RNS and RSS
The oxygen molecule (O2), despite having two unpaired electrons, is itself relatively stable. However, many oxygen-containing compounds, such as peroxides and superoxides, are highly reactive free radicals, collectively called “reactive oxygen species”. ROS are often byproducts of cellular energy production. Many, like superoxide, are actually produced by the body using specialized enzymes for specific purposes. Free radicals containing nitrogen are referred to as “reactive nitrogen species.” RNS result from the reaction of nitric oxide and superoxide to produce peroxynitrite, and related compounds. Both ROS and RNS are highly reactive, and can damage proteins, lipids and DNA. RNS-induced damage is sometimes referred to as “nitrosative stress, to distinguish it from “oxidative stress.”
Due to their destructive potential, superoxide and RNS are often produced by the body as a weapon to attack and destroy foreign pathogens. Superoxide production is tightly controlled by a highly regulated network of enzymes, see: Nox Family NADPH Oxidases. For more a more detailed overview of RNS, see: Nitric Oxide and Peroxynitrite in Health and Disease. Sulphur-containing radicals are referred to as “RSS” (reactive sulphur species).(ref) These result from the reaction of thiols with ROS. Both RNS and RSS result from reactions involving ROS. I will use the terms “ROS” and “OS” (oxidative stress) loosely, without differentiating between the effects caused by specific types of secondary radicals.
Radicals in Biology
Prior to their discovery in biological processes, radicals were already well-known for their reactive, and destructive power in other areas of chemistry. Oxidative injury caused by ionizing radiation was graphically demonstrated in Nagasaki and Hiroshima. The symptoms of oxidative damage resulting from exposure to nuclear radiation closely resembled the degenerative effects of aging. In 1954 oxygen toxicity was shown to be the result of radical formation.(ref) In 1956, Denham Harman published his seminal Free Radical Theory of Aging. In 1972, Harman identified the mitochondria as the primary source of cellular ROS generation. Much research focused on mitochondrial ROS (mtROS), in particular the possibility of mtROS “leakage” to other cellular compartments, and the effects of oxidative damage to sensitive mitochondrial DNA (mtDNA). Subsequent research has shown that mtROS “leakage” is much less than originally thought. “The physiological level of ROS emission from mitochondria is negligible (as discussed in this review) and unlikely to be of any significance except as a signal.” (ref) Experiments have also shown that oxidase overexpression lowering mtOS and mtDNA mutations, does not increase lifespan. Furthermore, dramatically increased mutations in mtDNA (500 fold) produce no signs of accelerated aging. (ref) Focus has shifted to other organelles such as the peroxisomes (ref, ref, ref, ref, ref) and lysosomes (ref, ref,). Due to the role of lysosomes in recycling mitochondria, some have gone so far as to rename the “Mitochondrial Free Radical Theory of Aging” the “The Mitochondrial–Lysosomal Axis Theory of Aging.” (ref, ref).
Given the recognized destructive potential of ROS and the ability of antioxidants to neutralize them, why has antioxidant supplementation failed to produce consistent, positive outcomes, in many cases, causing harm, even increasing oxidative stress? In order to understand the answers, we need to first understand the body’s natural antioxidant defense mechanisms, and the biological function of ROS in human physiology.
The Body’s Natural Antioxidant Defenses
Long-lived species have developed sophisticated mechanisms for dealing with ROS and utilizing them. Controversy of Free Radical Hypothesis: “To be protected from potentially harmful effects of ROS, aerobic organisms evolved several specialized mechanisms. To detoxify ROS, they use system of antioxidants, including specific antioxidative enzymes, e.g. superoxide dismutase, catalase, glutathione peroxidase. . .This system consists of mostly degradative yet also other enzymes such as proteases, peptidases, phospholipases, acyl transferases, endonucleases, exonucleases, polymerases, ligases, etc., to cleave and replace irreversibly damaged macromolecules (Elliott et al. 2000). Importantly, the systems are integrated, they work in concert and their actions may be closely interconnected (Sies 1993; Berry and Kohen 1999; Gate et al. 1999)”.
Superoxide Dismutase (SOD) catalyzes the reduction of superoxide into hydrogen peroxide and water. In mammals, there are three isoforms which function in distinct cellular compartments. SOD1 is found in the cytosol and mitochondrial intermembrane. SOD2 is located in the mitochondrial matrix; and SOD3 functions in the extracellular space. (ref)
Glutathione Peroxidase (Gpx) transforms peroxides, especially lipid hydroperoxides, into water and alcohol. Specialized GPx forms function in distinct cellular compartments in specific tissue types. “Analysis of the selenoproteome identified five glutathione peroxidases (GPxs) in mammals: cytosolic GPx (cGPx, GPx1), phospholipid hydroperoxide GPx (PHGPX, GPx4), plasma GPx (pGPX, GPx3), gastrointestinal GPx (GI-GPx, GPx2) and, in humans, GPx6, which is restricted to the olfactory system. GPxs reduce hydroperoxides to the corresponding alcohols by means of glutathione (GSH). They have long been considered to only act as antioxidant enzymes. Increasing evidence, however, suggests that nature has not created redundant GPxs just to detoxify hydroperoxides. cGPx clearly acts as an antioxidant, as convincingly demonstrated in GPx1-knockout mice. PHGPx specifically interferes with NF-kappaB activation by interleukin-1, reduces leukotriene and prostanoid biosynthesis, prevents COX-2 expression, and is indispensable for sperm maturation and embryogenesis. GI-GPx, which is not exclusively expressed in the gastrointestinal system, is upregulated in colon and skin cancers and in certain cultured cancer cells. GI-GPx is a target for Nrf2, and thus is part of the adaptive response by itself, while PHGPx might prevent cancer by interfering with inflammatory pathways. In conclusion, cGPx, PHGPx and GI-GPx have distinct roles, particularly in cellular defence mechanisms. Redox sensing and redox regulation of metabolic events have become attractive paradigms to unravel the specific and in part still enigmatic roles of GPxs.”(ref) In addition to these six GPxs, two additional isoforms have recently been identified, GPx7 and Gpx8, which appear to function in the endoplasmic reticulum, where they enable the “productive use” of peroxides for the oxidative folding of proteins.(ref)
Catalase (CAT) uses iron to reduce peroxides. Hundreds of different forms are widely distributed in animal, plant and fungi tissues. Some contain manganese, and some are bifunctional catalase-peroxidases.(ref)
In addition to these principal antioxidant enzymes, the secondary antioxidant enzymes, thioredoxin (ref), glutaredoxin (ref), and peroxiredoxin (ref) systems also aid in the control, and selective removal, of ROS. The activity of all innate antioxidant enzymes is highly selective. They function in specific cellular compartments, within specific tissues, in response to specific signaling pathways, to reduce specific radical types. The body is able to increase or decrease their activity in target locations, as needed, to maintain ideal redox homeostasis. Antioxidant enzymes cannot be taken orally; it would not be advisable to do so, even if possible. Experiments with IV administration have not produced favorable results. Plasma levels are not the key, since redox activity must be differentially modulated within specific cellular compartments in specific tissue types.(ref, ref)
Unlike innate antioxidant defensive enzyme systems, nutritional antioxidants are nonenzymatic, meaning that they are not enzymes which catalyze redox reactions directly affecting pro-oxidant substrates. For the most part, they work by breaking oxidative chains, either by accepting (or donating) electrons, thereby eliminating the unpaired electron. They are inferior to the body’s natural enzymatic antioxidants, because they cannot be activated selectively in response to the continually changing redox status of specific cellular compartments. Their activity is indiscriminate. Since ROS serve many important functions (discussed below), neutralizing them is not always beneficial. Furthermore, by interfering with the normal signaling pathways that activate the body’s natural enzymatic defenses, in many cases, exogenous antioxidants can actually increase oxidative stress (OS).
I should also mention that certain botanical phenolic compounds appear to work indirectly. Rather than interrupt oxidative chains by directly reducing pro-oxidants, they appear to decrease OS through a variety of signaling pathways, some of which may result in upregulation of the body’s innate enzymatic antioxidants.(ref) This is true for the so called “hormetic” botanicals including catechins, quercetin, and curcumin which are actually mild pro-oxidants, even though they indirectly decrease OS.(ref, ref)
“Hormesis” is the idea that regular exposure to small amounts of toxins, or other forms of biological stress have salutory effects, by activating defensive mechanisms. The blog entry Hormesis and age retardation introduces hormesis and its possible relevancy as an anti-aging strategy. How increased oxidative stress promotes longevity and metabolic health: “Recent evidence suggests that calorie restriction and specifically reduced glucose metabolism induces mitochondrial metabolism to extend life span. In conflict with Harman’s free radical theory of aging (FRTA), these effects may be due to increased formation of reactive oxygen species (ROS) within the mitochondria causing an adaptive response that culminates in subsequently increased stress resistance assumed to ultimately cause a long-term reduction of oxidative stress. This type of retrograde response has been named mitochondrial hormesis or mitohormesis, and may in addition be applicable to the health-promoting effects of physical exercise in humans and, hypothetically, impaired insulin/IGF-1-signaling in model organisms. Consistently, abrogation of this mitochondrial ROS signal by antioxidants impairs the lifespan-extending and health-promoting capabilities of glucose restriction and physical exercise, respectively. In summary, the findings discussed in this review indicate that ROS are essential signaling molecules which are required to promote health and longevity. Hence, the concept of mitohormesis provides a common mechanistic denominator for the physiological effects of physical exercise, reduced calorie uptake, glucose restriction, and possibly beyond.”
Extending life span by increasing oxidative stress: “This review aims to summarize published evidence that several longevity-promoting interventions may converge by causing an activation of mitochondrial oxygen consumption to promote increased formation of reactive oxygen species (ROS). These serve as molecular signals to exert downstream effects to ultimately induce endogenous defense mechanisms culminating in increased stress resistance and longevity, an adaptive response more specifically named mitochondrial hormesis or mitohormesis. Consistently, we here summarize findings that antioxidant supplements that prevent these ROS signals interfere with the health-promoting and life-span-extending capabilities of calorie restriction and physical exercise. Taken together and consistent with ample published evidence, the findings summarized here question Harman’s Free Radical Theory of Aging and rather suggest that ROS act as primarily as essential signaling molecules to promote metabolic health and longevity.”
There is evidence that hormesis is the result of epigenetic adaptations. Hormesis and epigenetics: “Recent experimental studies clearly indicate that environmental fluctuations can induce specific and predictable epigenetic-related molecular changes, and support the possibility of adaptive epigenetic phenomenon. The epigenetic adaptation processes implying alterations of gene expression to buffer the organism against environmental changes support adaptability to the expected life-course conditions. It appears likely that adaptive epigenetic rearrangements can occur not only during early developmental stages but also through the adulthood, and they can cause hormesis, a phenomenon in which adaptive responses to low doses of otherwise harmful conditions improve the functional ability of cells and organisms. In this review, several lines of evidence are presented that epigenetic mechanisms can be involved in hormesis-like responses.” The pendulum appears to be swinging. In place of antioxidants, some are even beginning to call hormetic OS a cure for aging. See:
Stress to the Rescue: Is Hormesis a ‘Cure’ for Aging?
Hormesis Against Aging and Diseases
Nutritional Hormesis and Aging
Inflammatory modulation of exercise salience: using hormesis to return to a healthy lifestyle
The Paradox of Exercise
The fact that enzymatic antioxidants are produced in response to ROS may, in part, explain the so called “paradox of exercise”. Why else would an activity, which results in dramatically increased levels of toxic ROS, produce undisputed health benefits? This may also explain why most studies of antioxidant supplementation with exercise have shown little benefit. Some studies have even found a negative effect to antioxidant supplementation combined with exercise. Here are a few examples:
Ascorbic acid supplementation does not attenuate post-exercise muscle soreness following muscle-damaging exercise but may delay the recovery process,
Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance,
Antioxidants prevent health-promoting effects of physical exercise in humans: “Exercise increased parameters of insulin sensitivity (GIR and plasma adiponectin) only in the absence of antioxidants in both previously untrained (P < 0.001) and pretrained (P < 0.001) individuals. This was paralleled by increased expression of ROS-sensitive transcriptional regulators of insulin sensitivity and ROS defense capacity, peroxisome-proliferator-activated receptor gamma (PPARγ), and PPARγ coactivators PGC1α and PGC1β only in the absence of antioxidants (P < 0.001 for all). Molecular mediators of endogenous ROS defense (superoxide dismutases 1 and 2; glutathione peroxidase) were also induced by exercise, and this effect too was blocked by antioxidant supplementation. Consistent with the concept of mitohormesis [mitochondrial hormesis], exercise-induced oxidative stress ameliorates insulin resistance and causes an adaptive response promoting endogenous antioxidant defense capacity. Supplementation with antioxidants may preclude these health-promoting effects of exercise in humans.”
For a detailed discussion of the exercise-induced muscular effects of ROS, see Exercise-Induced Oxidative Stress: Cellular Mechanisms and Impact on Muscle Force Production: “Many early studies investigating exercise and free radical production focused on the damaging effects of oxidants in muscle (e.g., lipid peroxidation). However, a new era in redox biology exists today with an ever-growing number of reports detailing the advantageous biological effects of free radicals. Indeed, it is now clear that ROS and RNS are involved in modulation of cell signaling pathways and the control of numerous redox-sensitive transcription factors. Furthermore, physiological levels of ROS are essential for optimal force production in skeletal muscle. Nonetheless, high levels of ROS promote skeletal muscle contractile dysfunction resulting in muscle fatigue.”
Many Biological Functions of ROS
ROS are not merely toxic compounds. In recent years, research has only just begun to reveal some of the important functions of ROS. Space does not permit detailed discussion of the many beneficial roles of ROS in human physiology; however, below is an unsystematic sampling of examples with references for those who may be interested.
ROS play an intimate role in the processes of cellular energy production. Without them human life would not be possible. For an interesting discussion of the crucial role of bioenergetics in the development of complex life see: Bioenergetics, the origins of complexity, and the ascent of man. For an explanation of the basics of biological energy production, see: Energy Generation.
A redox switch in angiotensinogen modulates angiotensin release
Oxyl radicals, redox-sensitive signalling cascades and antioxidants
Hydrogen peroxide sensing and signaling
Reactive oxygen species in cell signaling
Thiol peroxidases mediate specific genome-wide regulation of gene expression
The redox regulation of thiol dependent signaling pathways in cancer
Thiol-Based Redox Switches in Eukaryotic Proteins
Direct oxidative modifications of signalling proteins in mammalian cells and their effects on apoptosis
Oxidative stress and cell signalling
Involvement of plasma membrane redox systems in hormone action
Sex hormones are electron mediators. Testosterone, estrogen and progesterone (as well as the catecholamine, adrenaline) are able to both donate and accept electrons. This ability to mediate redox reactions enables cellular communication without binding to their receptors. Electron emission by hormones and Adrenaline: communication by electron emission
Destruction of Pathogens and Infected Cells
The many roles of NOX2 NADPH oxidase-derived ROS in immunity
The superoxide-generating oxidase of phagocytic cells
Dendritic, Phagocyte and T-cell Regulation
ROS Level Defines Dendritic Cell Development
Developmental biology: A bad boy comes good
Induction of regulatory T cells by macrophages is dependent on production of ROS
Redox Imbalance in T Cell-Mediated Skin Diseases
Macrophages suppress arthritis development by producing ROS.
Activation of antibacterial autophagy by NADPH oxidases
Regulation of autophagy by ROS: physiology and pathology
Autophagy, reactive oxygen species and the fate of mammalian cells
The general case for redox control of wound repair
Wound Healing Essentials: Let There Be Oxygen
Redox Signals in Wound Healing
NADPH oxidase-mediated redox signaling: roles in cellular stress response, stress tolerance, and tissue repair
Regulation of cell proliferation by NADPH oxidase-mediated signaling: potential roles in tissue repair, regenerative medicine
Hydrogen peroxide mediates rapid wound detection
ROS as essential mediators of cell adhesion
Function of ROS during animal development
Redox control in mammalian embryo development
The Roles of Glutathione Peroxidases during Embryo Development
(As a side note, Q10 actually increases OS during pregnancy, while vitamin E reduces it, see: Effects of exogenous antioxidants on oxidative stress in pregnancy.)
Cell-Cycle – Apoptosis/Proliferation – Destruction of Malignant Cells
The redox state of a cell plays an important role in determining whether the cell survives and proliferates, or dies. Moderate amounts of free radicals tend to promote survival and poliferation, while high levels result in apoptosis (cellular death). See: Redox Regulation of Cell Survival and CELLULAR REDOX SYSTEMS
“Under physiologic conditions, the balance between production and elimination of ROS ensures the proper maintenance of cellular metabolism and other functions.”
REACTIVE OXYGEN SPECIES, CELLULAR REDOX SYSTEMS AND APOPTOSIS
Capsaicin fights cancer by inhibiting antioxidant defenses, increasing ROS
Role of Mitochondrial Electron Transport Chain Complexes in Capsaicin Mediated Oxidative Stress Leading to Apoptosis in Pancreatic Cancer Cells
ROS suppress cancer genes, while antioxidant defenses increase tumorigenesis Oncogene-induced Nrf2 transcription promotes ROS detoxification and tumorigenesis See, also: Redox regulation in cancer
Cardiovascular – Endothelial Function – Nitric Oxide
Mitochondrial ROS-mediated signaling in endothelial cells
Exercise and Endothelial Function
Hypothalamic Appetite Regulation
ROS sets melanocortin tone and feeding in diet-induced obesity
Insulin Production and Function
Insulin action is facilitated by insulin-stimulated ROS
ROS and uncoupling protein 2 in pancreatic β-cell function
Regulation of Insulin Signaling by Reactive Oxygen and Nitrogen Species
Association of Duoxes with Thyroid Peroxidase and Its Regulation in Thyrocytes
Dual oxidase, hydrogen peroxide and thyroid diseases
Modulation of neuronal stem cell differentiation by hypoxia and reactive oxygen species
Proliferative neural stem cells have high endogenous ROS levels that regulate self-renewal and neurogenesis
Cerebral Blood Flow Regulation by Nitric Oxide: Recent Advances
Mitochondrial preconditioning: a potential neuroprotective strategy
Fuel utilization by hypothalamic neurons: roles for ROS
ROS-dependent endothelin signaling
Antioxidant Efficacy Studies
This will be the focus of a separate, follow-up blog entry.
Reasons Why Antioxidant Supplementation Does Not Work
- May not reach target compartments, i.e. the mitochondria.
- Inactivate natural defensive enzyme systems.
- Disrupt important signal transduction pathways.
- Disrupt normal redox homeostasis.
- May have adverse effects on gene expression.
Even if antioxidant supplements don’t work, accumulated oxidative damage could still be the cause of aging and/or other conditions. Transgenic and knockout mice studies alter the expression of genes regulating the production of antioxidant enzymes. As already mentioned, such studies increasing or decreasing mitochondrial antioxidants, which alternatively increased or decreased the amount of corresponding mtOS, had no effect on lifespan, and produced no visible signs of aging. Similarly, a study increasing the rate of mitochondrial mutations by 500 fold produced no signs of aging, and no change in lifespan. Based on all available current evidence, it is very unlikely that accumulated oxidative damage is the general cause of aging. It may play a causal role in the development of certain specific pathologies, though evidence for this remains inconclusive.
End of the free radical theory of aging?
Is the Oxidative Stress Theory of Aging Dead? “A direct experimental test of the Oxidative Stress Theory of Aging is to alter the level of oxidative stress/damage and determine how these alterations affect lifespan. Using DNA recombinant technology, investigators over the past fifteen years have studied the effect of altering the expression of various components of the antioxidant defense system on lifespan; these studies are described in the Discussion. Below, we bring together all of the lifespan data that our group has conducted on transgenic/knockout mice with alterations in a wide variety of genes involved in the antioxidant defense system. These data demonstrate that almost all alterations in the antioxidant system of mice have no effect on lifespan.”
Since the free radical theory of aging is still recognized as a central if not the most-central theory of aging in the longevity science community, and since antioxidant supplementation has been thought to be unquestionably beneficial, the main messages of this post may be shocking to some. However, a few earlier posts in this blog have telegraphed that all is not well with these tenants. These posts include The free radical theory of aging. Is it really a theory of aging?, The anti-antioxidant side of the story and Another possible negative for antioxidants.
Caution Interpreting Data
I realize that readers of this review are likely to reply with some of the numerous studies purporting to demonstrate the health benefits of antioxidant supplementation. I do not deny that, in certain cases, there may be some benefits. Since these are already widely-touted, I have intentionally focused on the possible adverse effects of nutritional antioxidants, and the many positive physiological functions of ROS, in order to present a more balanced view. I suggest that caution be exercised when interpreting data. The following points may seem obvious; but they remain common fallacies committed routinely by both laymen, and even researchers in the field.
- Correlation is not causation. The fact that aging or other conditions are associated with increased levels of OS does not show that OS causes those conditions.
- In vivo effects are often very diffferent from in vitro. The fact that a compound exhibits certain properties in the lab does not mean it will have the same effects in the complex environment of a living organism.
- Effects vary between species. The fact that a certain treatment increases the lifespan of a nematode, for example, does not imply that it will do the same for humans.
- More is not better. If a nutrient has a beneficial effect at a given dose, it does not follow that greater doses will produce a greater beneficial effect.
- Many nutritional antioxidants have important health benefits independent of their antioxidant activity. In certain cases, correcting nutritional deficits may produce benefits. It does not follow that the benefits are necessarily the result of antioxidant activity.
- Viable anti-aging therapies must be capable of increasing maximum human lifespan, not just mean lifespan.
What does the future hold for antioxidant research?
TThe Free Radical Theory of Aging appears to be dying, if not already dead. Nutritional antioxidant supplementation does not appear to be the key to improved improved health or longevity. Does this mean antioxidants are a dead-end? No. Pharmaceutical or nutraceutial antioxidant therapies remain promising. Given the fact that antioxidant defenses diminish (as do most biological processes) with age, upregulating these defenses through pharmaceutical or nutraceutical intervention may, one day, be part of a comprehensive anti-aging program. Such therapies may not dramatically increase lifespan; but they are likely to increase healthspan, and may prove to be an effective treatment for specific disorders. To be effective such therapies must selectively target the activation of compromised, or suboptimal antioxidant systems. Like all proteins, enzymatic antioxidants are the result of the expression of their genes. So, viable therapeutic approaches might seek to increase the expression of those genes. The Nrf2 ARE (Antioxidant Response Element) controls the expression of enzymatic antioxidants. Clinical trials are already underway for compounds targeting the Nrf2-ARE pathway.(ref) An alternate approach is to target the upstream or downstream effects of oxidative damage in specific cellular systems. As an example of the latter, Cause and Consequence discusses stategies for targeting KGDHC (α-ketoglutarate dehydrogenase complex), which plays a role in neurodegeneration. To be effective both approaches will require a detailed understanding of the molecular processes involved, rather than the indiscriminate ingestion of compounds thought to “reduce” evil ROS. Even highly selective approaches are likely to involve some trade-offs. The prevention of some degenerative conditions might come at the price of increased the risk of certain cancers, etc. Optimal health and longevity result from seeking a judicious balance. Very few physiological pathways are purely “evil”.
Trashing the time-worn oxidative damage theory of aging and re-examining the roles of antioxidant supplements involve major paradigm shifts for the aging sciences community. Much more can and should be said than can be comprised in this single blog entry. Both Dr. Giuliano and I expect to be contributing additional blog discussions relating to aspects of this paradigm shift.
I’ll simply point out the obvious contradiction between the life extension regimen you’re practicing and the opinion on antioxidants you’re expressing in the blog:
Nearly every supplement in your anti-aging firewalls program has *significant* exogenous antioxidant activity (irrespective of the reasons why you’re taking them, e.g. to control the expression of genes). Nearly every food choice you recommend also has significant exogenous antioxidant activity.
Are we now to believe that these supplements/foods “disrupt important signal transduction pathways”, “disrupt normal redox homeostasis”, “have adverse effects on gene expression”?
Certainly the issue of exogenous antioxidants and health is far more complicated than a simple reduction to: good vs bad.
Regarding Victor’s blog on antioxidants, I am very aware of what you are pointing out and currently writing an editorial-type blog entry addressing exactly that issue. You summarized the main consideration in your final sentence. It is no longer a sweeping game where antioxidant=good and radicals=bad. And I am not convinced that exogenous antioxidant activity always=bad. It is a much more complex situation in which antioxidant activity of a substance may be secondary or tertiary in its importance compared to other properties such as pathway activation, inhibition of NF-kappaB, epigenomic impact, etc.. In some cases such as major exposure to radiation, taking a strong mix of antioxidant supplements is probably well justified. Dozens of substances in my regimen are incidentally antioxidants yet my intent was to only include substances with research-demonstrated health impacts. I don’t care if blueberries, green tea, curcumin, resveratrol, etc. are antioxidants given ample research that the net effects of these substances are health-positive. It looks like we are going to have to look at substances and combinations of substances from much more sophisticated viewpoints than we have been. I will be striving to adjust my suggested regimen accordingly.
Some Russian research with targeted Mitochondria antioxidents:
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Thanks very much for your response and for your blog. I enjoy reading it each week.
I am conforted by the overwhelming epidemiological evidence on fruits and vegetables. In most cohort studies and clinical trials, the higher the intake of fruits and vegetables, the lower the risk for a variety of diseases. I am the first to admit that this in no way demostrates causality. Exogenous antioxidants are obviously confounded with many other variables that may be responsible, e.g. the multiple effects of phytochemicals on gene expression.
However, it is very much a myth to believe that the ORAC value of taking multiple supplements a day cannot easily be surpassed by diet alone. One only need consume 10 glasses of fresh low-GI high-ORAC vegetable/fruit juices a day (made fresh with a juicer) to achieve a total ORAC intake that is absolutely enormous. I doubt that a single author on any of the references Victor sites would state that such large consumption of fruit/vegetable juices is unhealthy. The epidemiologal evidence whole-heartedly supports the 10 glasses a day regimen.
The inverse *association* between ORAC intake in fruit/vegetables and multiple disease risks is absolutely striking. The ORAC score may simply be a surrogate marker for something else producing the health effects. Then again, it may not. It may be the endogenous antioxidants themselves. Keep in mind that there are hundreds of thousands, perhaps millions, of phytochemicals with exogenous antioxidant activity. Less than a dozen have been studied with any rigor in clinical trials. With hundreds of thousands still to go, it’s quite possible that we haven’t studied the right antioxidants yet. To jump from specific results on less than a dozen compounds to a broad generalization on hundreds of thousands of compounds is very much unwarranted, in my opinion.
Even the results of the tiny number of clinical trials that have been completed on antioxidants are very controversial in terms of good vs neutral vs bad, despite the implication in your blog that all the evidence uniformly points to neutral or bad. Take Vitamin E, for example (no antioxidant has been beaten up more). For a fair and balanced view on clinical trial evidence regarding Vitamin E, read Walter Willet’s synopsis on the Harvard School of Public Health site:
Walter Willett (author of over 1000 medline-indexed journal articles, and the second most medline-cited author in all of medicine) clearly does NOT believe that there is no positive clinical trial evidence in the case of this particular antioxidant. In fact, he cites quite a bit of positive trial results. This situation is not unique for Vitamin E — a fair and balanced review can cite plenty of positive clinical trial results for other antioxidants as well, in addition to the large majority of neutral results, and a several bad results.
I follow 2 simple rules of thumb, in my own choices of supplements:
1. Try to stick with whole extracts of fruits/vegetables as much as possible. For example, standardized herbs and botanicals.
2. Only deviate from this rule when there is strong evidence of benefit. For example, with resveratrol, quercetin, pterostilbene, etc.
3. Avoid taking a supplement if its only real value is as an exogenous antioxidant, or if it is an extremely powerful endogenous antioxidant even though it may have other purported benefits. For example, I avoid NAC (as I notice you do), primarily because its endogenous antioxidant activity is so extremely strong.
The central point of this blog entry was to correct the erroneous view of ROS as purely harmful compounds. ROS play critical roles in many fundamental cellular processes. The misguided quest to indiscriminately eradicate ROS by consuming nutritional antioxidants (in any form) is based on a simplistic, outdated understanding of their role in human physiology. Although mentioned, human efficacy studies were not the focus of this blog post. For those interested in such studies, I will provide a list of references in a future entry. However, given the recent advances in our understanding of the many important roles of ROS and the body’s innate mechanisms to maintain redox balance, it is not at all surprising that clinical studies of antioxidant supplementation have been disappointing. I am not making any generalizations based on these studies, merely pointing out that they are not at all surprising, and that they confirm that something was lacking from the earlier, now outdated, theory of ROS. I agree with Walter Willett that certain nutritional antioxidants may prove to be beneficial for specific disorders, or specific genetic defects. However, it is unlikely that they will ever be effective at preventing aging, which does not appear to be the result of accumulated oxidative damage.
Please excuse the typos in the previous response. It was written in haste. In particular, I accidently write “endogenous” when I mean “exogenous” in several locations, e.g. in referring to the antioxidants in fruits/vegetables and in referring to NAC. My apologies for the sloppiness.
I agree with your central point.
>> However, it is unlikely that they will ever be effective at preventing aging, which does not appear to be the result of accumulated oxidative damage.
Yet on this final point I disagree: There is now good emerging evidence that premature shortening of telomeres is in large part induced by free radicals. The radicals cleave the ends of the chromosome, and thereby reduce the length of the telomere. Strategies to boost endogenous production of antioxidants, coupled with judicious use of exogenous antioxidants that complement these strategies may be a means to prevent this aspect of premature aging. Such a strategy would never decrease the basal rate of telomere shortening, and could therefore never be expected to extend maximum lifespan. However, it could in theory produce an increase in mean lifespan.
The theory could only be tested in large mammals that age telomerically, such as humans. Previous experiments with antioxidants in mice, drosophila, c. elegans, etc. are irrelevant because these animals do not age primarily by means of telomere mechanisms. Valid animal models are dogs, cats, horses, deer, etc.
If such a theory were correct (which I believe it is), it would take decades of antioxidant supplementation for an overt reduction in chronic disease risk to become apparent. For example, it may take 25 years of antioxidant supplementation to see a modest 5% difference in mean telomere length between a variable group taking antioxidants and a control group not taking them. In addition to likely studying the wrong antioxidants for optimal telomere protection, previous clinical trials have not been run for a long enough duration to have any real statistical power in detecting an overt reduction in disease risk by telomere mechanisms. However, many cohort studies like the Harvard Nurse’s Study are now approaching durations where such effects could conceivably be detected. For example, in the Harvard Physician’s Health Study, it took 18 years for a protective effect of beta carotene supplementation on brain function to finally show up. But when it recently did show up, the effect was significant, and older men who took the antioxidant performed better on memory tests than men who did not. Such an effect could conceivably be explained by modestly longer telomeres in the brains of the men taking the antioxidant.
So I disagree that it “unlikely” that antioxidants will ever be effective at preventing aging. I believe that it is in fact very likely that antioxidants (particularly the endogenous variety) prevent premature shortening of telomeres, and thereby slow human aging via telomere mechanisms. This view is based strongly on the hypothesis that the telomere theory of aging dominates over the other theories of aging (which I strongly believe is true) — and that most of the other theories of aging are actually consequences of short telomeres, and not fundamental causes of aging in their own right.
Brand new animal study, perhaps providing some support for my hypothesis above:
In light of the bodies Hormetic response, I found this kinda interesting. Those world class athletes that utilize the highest amount of O2 live longest. They certainly don’t die young
Sorry forgot to provide that llink
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Vince, the latest in-vitro study on resveratrol is giving me the shakes. I’ve been taking it for several years.
Antioxidants, Resveratrol DAMAGE DNA:
Please let me know if you intend to continue talking resveratrol and what your thoughts are about the above study.
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As much as I refused to accept the death of antioxidant approaches to aging, I am slowly coming around.
I just read this:
Metformin promotes lifespan through mitohormesis via the peroxiredoxin PRDX-2
“We reveal a signaling cascade in which metformin is able to extend lifespan by increasing the production of reactive oxygen species .”
Increasing the production of ROS!!!
Who’d a thunk it.
Being a member of LEF, I have also seen a radical departure (unspoken) from the antioxidant product approach, to one of emphasizing glycation, phyto-substances, enzymes and coenzymes, like NAD+ and AMPK, etc.
You guys were way ahead of anyone on this.
Another interesting article along the same lines: