By Marie Spano, M.S., R.D., Contributing Editor
Nutrition has a profound effect on immune-system function. In fact, “70% of the immune system is located in the digestive system, so a digestive system that is operating in a healthy fashion is only going to help the immune system," notes Carl Freund, vice president of consumer products, Ganaden, Cleveland. Therefore, immune-boosting products, from vitamins to probiotics to phytochemicals, are rising market stars. But the science needs to support the marketing claims.
Vital vitamins
Vitamin A is essential for maintaining the lining of mucous membranes, helping immune-system cells fight infections more effectively and regulating the immune system (Nutrition and Health, 1996; 10(4):285-312). Though vitamin A can be toxic in very large doses, provitamin A carotenoids are considered safe because the body’s conversion to vitamin A stops when stores are full. However, because of conflicting studies about the potential adverse effects of beta-carotene in some populations, the Institute of Medicine Food and Nutrition Board, Washington, D.C., indicates that beta-carotene is not advisable for the general population
Epidemiological studies have linked inadequate vitamin D levels to a greater susceptibility of chronic infections and autoimmune diseases such as type 1 diabetes (Current Opinions in Pharmacology, 2010; 10:482-496). And, because many experts and scientific papers describe a state of vitamin D deficiency and insufficiency across the globe (American Family Physician, 2009; 80:841-846), the media attention to vitamin D has put this vitamin on the radar of many consumers.
Vitamin E affects the immune system, and supplementation above currently recommended levels can improve overall immune-system function and reduce the rate of upper-respiratory infections in the elderly (Journal of Lueukocyte Biology, 2008; 84:900-914; Immunological Reviews, 2005; 205:269-284).
Micro-importance
Some strains of probiotics, beneficial microorganisms, can replace the healthy bacteria in our bodies, enhance immune functioning, improve colonic integrity and help protect us against microorganisms that could cause disease, according to the National Institutes of Health National Center for Complementary and Alternative Medicine, Bethesda, MD.
For a probiotic to be effective, it must survive the manufacturing process, as well as shipping and storage. However, there is some debate about whether or not probiotics must adhere to mucosal cells in order to be effective. Probiotics pass through the small intestine, and those that survive intestinal transit establish themselves for a short period of time in the large intestine (American Journal of Clinical Nutrition, 1991; 73(2):399S-405S).
Because only a certain percentage of probiotics survive their trip through the intestines, and they may or may not adhere to intestinal mucosal cells, supplemental probiotics need to be taken continuously for a sustained effect, making frequently consumed foods and beverages the most effective candidates for probiotic fortification. Each species and strain of probiotics is different, and if immune health is the objective, it is critical to choose a species and strain that is backed by sound clinical research.
Prebiotics such as fructooligosaccharides and oliogosaccharides also benefit the immune system by stimulating the production of nonpathogenic intestinal microflora (Journal of Physiology and Biochemistry, 2009; 65:315-328).
Polysaccharide balance
With the popularity of gluten-free diets, one may think that going gluten-free has no disadvantages. However, two studies examining gluten-free diets in healthy individuals found that this diet resulted in a decrease in healthy gut bacteria and an increase in unhealthy gut bacteria (Gut Microbes, 2010; 1:135-137; British Journal of Nutrition, 2009; 102:1,154-1,160).
