Found this interesting article which provides study-based information and health tips taken from a report by Harvard Health Publications. I've reposted only the parts about potentially beneficial supplements. The remainder of this article explores several other connections between lifestyle and health.
If you suspect your diet is not providing you with all your micronutrient needs — maybe you don’t like vegetables or you choose white bread over whole grains — taking a daily multivitamin and mineral supplement brings health benefits of many types, beyond any possibly beneficial effects on the immune system. Taking megadoses of a single vitamin does not. More is not necessarily better. Researchers are investigating the immune boosting potential of a number of different nutrients.
Selenium. Some studies have suggested that people with low selenium levels are at greater risk of bladder, breast, colon, rectum, lung, and prostate cancers. A large-scale, multiyear study is currently in progress to look at the effects of combining selenium and vitamin E on prostate cancer prevention.
Vitamin A. Experts have long known that vitamin A plays a role in infection and maintaining mucosal surfaces by influencing certain subcategories of T cells and B cells and cytokines. Vitamin A deficiency is associated with impaired immunity and increased risk of infectious disease. On the other hand, according to one study, supplementation in the absence of a deficiency didn’t enhance or suppress T cell immunity in a group of healthy seniors.
Vitamin B2. There is some evidence that vitamin B2 enhances resistance to bacterial infections in mice, but what that means in terms of enhancing immune response is unclear.
Vitamin B6. Several studies have suggested that a vitamin B6 deficiency can depress aspects of the immune response, such as lymphocytes’ ability to mature and spin off into various types of T and B cells. Supplementing with moderate doses to address the deficiency restores immune function, but megadoses don’t produce additional benefits. And B6 may promote the growth of tumors.
Vitamin C. The jury is still out on vitamin C and the immune system. Many studies have looked at vitamin C in general; unfortunately, many of them were not well designed. Vitamin C may work in concert with other micronutrients rather than providing benefits alone.
Vitamin D. For many years doctors have known that people afflicted with tuberculosis responded well to sunlight. An explanation may now be at hand. Researchers have found that vitamin D, which is produced by the skin when exposed to sunlight, signals an antimicrobial response to the bacterium responsible for tuberculosis, Mycobacterium tuberculosis. Whether vitamin D has similar ability to fight off other diseases and whether taking vitamin D in supplement form is beneficial are questions that need to be resolved with further study.
Vitamin E. A study involving healthy subjects over age 65 has shown that increasing the daily dose of vitamin E from the recommended dietary allowance (RDA) of 30 mg to 200 mg increased antibody responses to hepatitis B and tetanus after vaccination. But these increased responses didn’t happen following administration of diphtheria and pneumococcal vaccines.
Zinc. Zinc is a trace element essential for cells of the immune system, and zinc deficiency affects the ability of T cells and other immune cells to function as they should. Caution: While it’s important to have sufficient zinc in your diet (15–25 mg per day), too much zinc can inhibit the function of the immune system.
Scientists have looked at a number of herbs and vitamins in terms of their potential to influence the immune system in some way. Much of this research has focused on the elderly, children, or people with compromised immune systems, such as AIDS patients. And many of the studies have had design flaws, which means further studies are needed to confirm or disprove the results. Consequently, these findings should not be considered universally applicable.
Some of the supplements that have drawn attention from researchers are these:
Aloe vera. For now, there’s no evidence that aloe vera can modulate immune response. Because many different formulations and compounds have been used in studies, comparing the results is difficult. However, there is some evidence that topical aloe vera is helpful for minor burns, wounds, or frostbite, and also for skin inflammations when combined with hydrocortisone. Studies have found aloe vera is not the best option for treating breast tissue after radiation therapy.
Astragalus membranes. The astragalus product, which is derived from the root of the plant, is marketed as an immune-system stimulant, but the quality of the studies demonstrating the immune-stimulating properties of astragalus are poor. Furthermore, it may be dangerous.
Echinacea. An ocean of ink has been spilled extolling echinacea as an “immune stimulant,” usually in terms of its purported ability to prevent or limit the severity of colds. Most experts don’t recommend taking echinacea on a long-term basis to prevent colds. A group of physicians from Harvard Medical School notes that studies looking at the cold prevention capabilities of echinacea have not been well designed, and other claims regarding echinacea are as yet not proven. Echinacea can also cause potentially serious side effects. People with ragweed allergies are more likely to have a reaction to echinacea, and there have been cases of anaphylactic shock. Injected echinacea in particular has caused severe reactions. A well-designed study by pediatricians at the University of Washington in Seattle found echinacea didn’t help with the duration and severity of cold symptoms in a group of children. A large 2005 study of 437 volunteers also found that echinacea didn’t affect the rate of cold infections or the progress and severity of a cold.
Garlic. Garlic may have some infection-fighting capability. In laboratory tests, researchers have seen garlic work against bacteria, viruses, and fungi. Although this is promising, there haven’t been enough well-designed human studies conducted to know whether this translates into human benefits. One 2006 study that looked at rates for certain cancers and garlic and onion consumption in southern European populations found an association between the frequency of use of garlic and onions and a lower risk of some common cancers. Until more is known, however, it’s too early to recommend garlic as a way of treating or preventing infections or controlling cancer.
Ginseng. It’s not clear how the root of the ginseng plant works, but claims on behalf of Asian ginseng are many, including its ability to stimulate immune function. Despite the claims of a number of mainly small studies, the National Center for Complementary and Alternative Medicine (NCCAM) considers there have been insufficient large studies of a high enough quality to support the claims. NCCAM is currently supporting research to understand Asian ginseng more fully.
Glycyrrhiza glabra (licorice root). Licorice root is used in Chinese medicine to treat a variety of illnesses. Most studies of licorice root have been done in combination with other herbs, so it’s not possible to verify whether any effects were attributable to licorice root per se. Because of the potential side effects of taking licorice and how little is known about its benefits — if any — for stimulating immune function, this is an herb to avoid.
Probiotics. There are hundreds of different species of bacteria in your digestive tract, which do a bang-up job helping you digest your food. Now researchers, including some at Harvard Medical School, are finding evidence of a relationship between such “good” bacteria and the immune system. For instance, it is now known that certain bacteria in the gut influence the development of aspects of the immune system, such as correcting deficiencies and increasing the numbers of certain T cells. Precisely how the bacteria interact with the immune system components isn’t known. As more and more intriguing evidence comes in to support the link that intestinal bacteria bolster the immune system, it’s tempting to think that more good bacteria would be better. At least, this is what many marketers would like you to believe as they tout their probiotic products.