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Reactive Oxygen Species -- Summary
Reactive oxygen species (ROS) are generated by the normal metabolism of animal cells and create oxidative stresses in organisms that tend to shorten their lives. This negative consequence of ROS, according to Finkel and Holbrook (2000), is largely counteracted by "an intricate antioxidant defense system," and they say that the components of this system "that increase resistance to stress should have anti-ageing benefits and lead to enhanced life span."

In a comprehensive review of the negative impacts of ROS and other free radicals that promote oxidative stress in humans, Willcox et al. (2004) report that this condition (oxidative stress) "has been related to cardiovascular disease, cancer, and other chronic diseases that account for a major portion of deaths today." In addition, they discuss the role that exogenous antioxidants play in controlling oxidation and review the evidence for their roles in preventing disease.

The three nutrition experts begin their discussion of this important subject by stating that "diet plays a vital role in the production of the antioxidant defense system by providing essential nutrient antioxidants such as vitamin E, C, and -carotene, other antioxidant plant phenols including flavanoids, and essential minerals that form important antioxidant enzymes." In addition, they note that "epidemiological data generally indicate a benefit of consuming diets that are higher in antioxidant nutrients, specifically diets high in fruits and vegetables."

But isn't it much easier to obtain these antioxidants by simply popping a pill or two into one's mouth? It certainly is; and millions of people do it daily. But is this approach as effective as obtaining needed antioxidants via the foods one eats? Probably not.

Willcox et al. write that in many studies of antioxidant health benefits "it is not clear whether the benefit is derived from the specific nutrients under study or another food component having health benefits yet to be discovered," or that perhaps "there is a particular combination of antioxidant nutrients that provide protection." While some epidemiological studies, in their words, "appear to demonstrate clear associations, direct tests of the relationships with clinical trials have not yielded similar results." In fact, they say "the most convincing evidence of antioxidant effect on cancer prevention involves feeding fruits and vegetables [our italics] rather than individual antioxidants."

Our reason for reporting these observations is that atmospheric CO2 enrichment has been documented to enhance the concentrations of a number of antioxidants in many of the foods we eat, as may be readily verified by perusing the materials we have archived in our Subject Index under the headings of Antioxidants and Health Effects (CO2 - Health-Promoting Substances). In what follows, therefore, we merely report the results of two studies that have confirmed the positive effects of antioxidant-induced decreases in animal ROS concentrations on animal life span.

Melov et al. (2000) tested the theory that reactive oxygen species cause aging by examining the effects of two superoxide dismutase-/catalase-like mimetics (EUK-8 and EUK-134) on the life-span of normal and mutant Caenorhabditis elegans worms that ingested various concentrations of the mimetics. In all of their experiments, treatment of normal worms with the antioxidant mimetics significantly increased both mean and maximum life-span. Treatment of normal worms with but 0.05 mM EUK-134, for example, increased their mean life-span by fully 54%; and in mutant worms whose life-span had been genetically shortened by 37%, treatment with 0.5 mM EUK-134 restored their life-span to normal by increasing their mutation-reduced life-span by 67%. It was also determined that these effects were not due to a reduction in worm metabolism, which could have reduced the production of oxygen radicals, but "by augmenting natural antioxidant defenses without having any overt effects on other traits." In other words, in the words of the authors, "these results suggest that endogenous oxidative stress is a major determinant of the rate of aging," the significance of which statement resides in the fact that antioxidants tend to reduce such stresses in animals, including man, and in the observation that atmospheric CO2 enrichment has been shown to significantly enhance the concentrations of many of these important ROS-fighting constituents of the foods we eat.

Another study to address the subject was conducted by Larsen and Clarke (2002), who fed diets with and without coenzyme Q to wild-type Caenorhabditis elegans and several mutants during the adult phases of their lives, while they recorded the lengths of time they survived. This work revealed that "withdrawal of coenzyme Q from the diet of wild-type nematodes extends adult life-span by ~60%." In addition, they found that the life-spans of the four different mutants they studied were extended by a Q-less diet. More detailed experiments led them to conclude that the life-span extensions were due to reduced generation and/or increased scavenging of reactive oxygen species, leading them to conclude in the final sentence of their paper that "the combination of reduced generation and increased scavenging mechanisms are predicted to result in a substantial decrease in the total cellular ROS and thereby allow for an extended life-span."

In light of these many diverse observations of both plants and animals, there is ample reason to believe that the historical increase in the air's CO2 content has played a prominent role in enhancing many aspects of human health over the course of the Industrial Revolution, and that its continued upward trend will provide ever more of the same benefits, not the least of which is increased longevity. Consequently, we end this summary with the encouraging thought that perhaps the best way to obtain these benefits is to directly consume foods that are known to contain high levels of antioxidants, i.e., fruits and vegetables, since with each passing year these foods will likely contain ever greater concentrations of ROS-fighting substances, thanks to the ongoing rise in the air's CO2 content that comes primarily from the burning of fossil fuels.

References
Finkel, T. and Holbrook, N.J. 2000. Oxidants, oxidative stress and the biology of ageing. Nature 408: 239-247.

Larsen, P.L. and Clarke C.F. 2002. Extension of life-span in Caenorhabditis elegans by a diet lacking coenzyme Q. Science 295: 120-123.

Melov, S., Ravenscroft, J., Malik, S., Gill, M.S., Walker, D.W., Clayton, P.E., Wallace, D.C., Malfroy, B., Doctrow, S.R. and Lithgow, G.J. 2000. Extension of life-span with superoxide dismutase/catalase mimetics. Science 289: 1567-1569.

Willcox, J.K., Ash, S.L. and Catignani, G.L. 2004. Antioxidants and prevention of chronic disease. Critical Reviews in Food Science and Nutrition 44: 275-295.

Last updated 7 May 2008