Free-radical Theory of Aging - Antioxidant Therapy

Antioxidant Therapy

The free radical theory of aging implies that antioxidants such as vitamin A, vitamin C, vitamin E (alpha-tocopherol), beta-carotene and Superoxide dismutase will slow the process of aging by preventing free radicals from oxidizing sensitive biological molecules or reducing the formation of free radicals. The antioxidant chemicals found in many foods are frequently cited as the basis of claims for the benefits of a high intake of vegetables and fruits in the diet.

Nonetheless, some recent studies tend to show that antioxidant therapy have no effect and can even increase mortality. One example is the ATBC (Alpha-Tocopherol Beta Carotene) study containing 29,133 male smokers in Finland aged 50–69 years. The premise suggested high fruit and vegetable intake protected against lung cancer and smokers have lower serum retinol concentrations. Participants were given either Vit E (50 mg), beta-carotene, (20 mg), both, or a placebo daily for 5–8 years. Results found 18% more lung cancer and 8% higher mortality with beta-carotene (effect only seen in drinkers) and 32% decrease in incidence of prostate cancer in group taking Vit E. The Beta-Carotene and Retinol Efficacy Trial (CARET) including 14,000 smokers and ex-smokers 50–69 years old consisting of beta-carotene (30 mg) and retinol (25,000 IU). Results suggested 28% more cancer and 17% greater mortality. ATBC and CARET follow up studies were also conducted. A study conducted 6 years post the ATBC study indicated that the higher rates of lung cancer and effect on prostate cancer were reduced. The CARET follow up study showed reduced lung cancer, however, risk remained elevated in females. Other studies suggested no reduction in cancer following antioxidant supplementation. Additionally, the Physician Health Study containing 22,000 males, 11% smokers, found beta-carotene supplementation was not harmful after 12 years, 44% lower risk of adenoma recurrence in non-smokers and drinkers, but double the risk in smokers and drinkers.

However, in 2004 the SU.VI.MAX study found providing low dose, combination supplementation in doses easily achievable in an everyday diet decreased incidence of cancer by 31% and reduced all-cause mortality by 37%.

Overall, results from a meta-analysis study indicated whether taking a placebo or an anti-oxidant supplement showed no overall benefit.

Since many different substances operate synergistically in anti-oxidant defence, its complicated process may require more sophisticated approaches to determine if antioxidant therapy may benefit the aging process.

Proponents of the theory claim that this phenomenon can be explained by hormesis: The addition of antioxidants can lead to a decrease of normal biological response to free radicals and lead to a more sensitive environment to oxidation. Furthermore, a recent study tracking the eating habits of 478,000 Europeans suggests that consuming lots of fruits and vegetables has little if any effect on preventing cancer. More recently, it has been suggested that in humans extraordinarily-high levels of endogenous antioxidants such as uric acid do not leave a lot of "therapeutic room" for ectopic antioxidants to work.