The immune system defends the body against invading microbes such as bacteria and viruses. Many supplement manufacturers claim their products support immunity. But so far, there is not enough scientific evidence to back up the claims. The reason, according Michael N. Starnbach, Ph.D., the Harvard Medical School expert who edited The Truth About Your Immune System, is that science has not yet determined what level of immune system cells will best help the body resist disease. While some proponents of vitamins and supplements claim that boosting the number of immune cells improves immunity, that link has yet to be established. The variety of immune cells is vast, and their interactions remain largely unknown.

The Truth About Your Immune System explains what scientists do know about human immunity and also describes areas under investigation, including the development of new vaccines and the influence of lifestyle on immunity. So far, the report says, the lifestyle factors that appear to help keep the immune system in shape are the same ones that promote overall health, such as these:

avoiding tobacco eating a diet high in fruits, vegetables, and whole grains, and low in saturated fat exercising regularly maintaining a healthy weight controlling your blood pressure drinking only in moderation (if at all) getting adequate sleep taking steps to avoid infection, such as washing your hands frequently and preparing foods safely.

Dr. Starnbach, the editor of the 43-page report, is a professor of microbiology and molecular genetics at Harvard Medical School.

The Truth About Your Immune System: What you need to know is available for $16 from Harvard Health Publications, the publishing division of Harvard Medical School. Order it online at health.harvard/E or by calling 1-877-649-9457 (toll free).

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Currently, approximately 65 percent of U.S. adults are overweight or obese, according to the National Institutes of Health. Research suggests that overweight individuals appear to be on the pathway to obesity. Overweight and obesity are associated with an increased risk of developing health problems such as hypertension, type 2 diabetes and heart disease. Factors that can contribute to overweight include an abundance of high-calorie foods, low levels of physical activity, behavior, environment, and genetics. Multiple studies have shown that a modest reduction in weight improves health outcomes significantly in overweight or obese patients.

About the Survey

The initial survey, which was the source of this analysis, was conducted between November 18, 2005 and January 10, 2006, with a hiatus over the holidays, by The Center for Survey Research & Analysis (CSRA) at the University of Connecticut, a non-partisan, non-profit survey research facility dedicated to the study of public opinion.

Using random digit-dialing, 64,025 telephone numbers were dialed and 12,599 households were reached. A sample of 3,500 people completed the in-depth telephone interview for a response rate of 28 percent. The maximum expected sampling error associated with a sample of this size would be 1.66 percentage points at the 95 percent confidence level. The survey was funded by GlaxoSmithKline Consumer Healthcare.

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