As we age the rate of free radical formation within our bodies increases. At the same time aging is also associated with a decline in immune system function increasing our susceptibility to infections, cancer, autoimmune diseases (i.e. Lupus) and inflammatory conditions. Free radicals are known to suppress immune system function. Some researchers have proposed that antioxidant vitamins and related nutrients can improve immune system function as we age by virtue of their ability to reduce free radical production. Optimal concentrations of antioxidants are needed for maintenance of the immune response across all age groups, but this appears to be most critical in aged persons.
Complicating matters is the fact that elderly persons tend to ingest low levels of antioxidant nutrients. For example Garry et al reported that 50% of elderly persons (mean age 60 years) had intakes of vitamin E, vitamin C, and zinc that were less than two-thirds of the RDA (recommended daily allowance). The studies by Ryan, Panemangalore, Vatassery, Wilson and Linderman (see references) have all suggest that low antioxidant nutritional status is a common finding in older persons.
Several investigators are now exploring the role of antioxidant supplementation as a means to strengthen the immune system of aging persons in an attempt to reduce their risk of cancer, infections and other common age-related afflictions.
During the mid 1980's the first studies using vitamin E supplementation were performed to evaluate its effect on immune system function. The studies by Ziemlarski, Harmon and Miller, Cannon and Meydani were the first reported evidence that vitamin E supplements, ranging from 100-800 I.U. per day, could improve immune system parameters in elderly persons. Reporting in the December 1995 edition of the American Journal of Clinical Nutrition, Meydani et al summarize three other clinical trials that they performed with elderly persons using various vitamin E dosages. Overall the data suggest that vitamin E supplementation of elderly persons is beneficial to immune response. At amounts as high as 800 mg (for 4.5 months) no detrimental effects were seen.
It appears that vitamin E has other immune-enhancing effects over and above its antioxidant properties. Vitamin E supplementation also suppresses the formation of prostaglandin series 2, which in turn further reduces free radical production. As a result the body is able to proliferate lymphocytes, which are a key component of immune system function. Less prostaglandin series 2 enables the immune system to synthesize these needed lymphocytes which are necessary to ward off infections and produce antibodies.
Hence, vitamin E supplementation contributes to improved immune system function in several ways.
Beta-carotene is another antioxidant that is known to have immune-enhancing properties. In human studies Prabhala et al demonstrated that beta-carotene can significantly increase the percentage of natural killer cells. Barrett demonstrated that a 3 month trial of beta-carotene supplementation resulted in a 40% increase in natural killer cell activity, increased number of lymphocytes expressing 1L-2 receptor as well as natural killer cell markers. All of these adaptations are associated with improved immune system function. As well male vegetarians with serum beta-carotene concentrations twice those of male omnivores also showed a twofold greater natural killer activity. One of the functions of natural killer cells is to identify and kill cancer cells in the body. Thus, better natural killer cell activity is considered to be important for cancer prevention.
The potential cancer preventive effect of beta-carotene is of particular importance to elderly persons, whose cancer incidence is greatest. In a 1995 study, Santos and Meydani investigated the effects of beta-carotene supplementation in a healthy aging population. Natural killer cell activity was significantly greater in elderly persons ingesting a beta-carotene supplement when compared with elderly persons receiving the dummy pill (placebo). In this instance subjects ingested 50 mg of beta-carotene every other day for 10-12 years. 50 mg of beta-carotene is equivalent to 75,000-80,000 I.U. of beta-carotene, which is a dosage that would be difficult to acquire from food alone. The average daily consumption of beta-carotene in the U.S. is 6,000-10,000 I.U.
Santos and Meydani conducted a 3 week, randomized, double blind, placebo controlled beta-carotene supplementation trial to investigate the short-term effect of beta-carotene (90 mg per day) with subjects 60-80 years of age. In this study positive immune system changes were also evident (35% increase in the DTH skin response compared with baseline values). The researchers conclude that immunoenhancement of beta-carotene remains an attractive possibility for humans with sub optimal immune response, such as patients with precancerous lesions and healthy elderly persons.
Beta-carotene, like vitamin E, also appears to be able to suppress the formation of prostaglandin series 2, according to the work of Halevy (see references). Prostaglandin series 2 has been shown to suppress T cell-mediated immune function and natural killer cell-mediated immune function. Thus, any dietary intervention that blocks the formation of prostaglandin series 2 is desirable from a standpoint of immune system function.
The findings from all of these studies suggest that the age related decline in immune system function predisposes to increased risk of cancer, infection and related problems in old and elderly persons. At the same time, supplementation with vitamin E (i.e. 100-400 I.U.) and beta-carotene (i.e. 10,000-50,000 I.U.) have been shown to improve immune function in aged persons, reversing the age related decline of the immune system. Increased free radical formation with aging is likely a contributing factor to a weakening of the immune system. Antioxidants such as vitamin E and beta-carotene suppress free radical formation and have been shown to enhance immune system function in other ways.
In my view a prudent antioxidant supplementation program for aging persons is a logical step to help reduce their risk of cancer, infections and other conditions that are common with aging. Other nutrients such as vitamin C, selenium, and zinc are also important to immune system function and supplementation studies with each of these nutrients have demonstrated improvement in immune function as well.
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