Health professionals generally urge people to meet their nutrient needs with a varied diet rather than with dietary supplements. The reason this is preferable is because foods contain many beneficial components in addition to essential nutrients. Still, there are some good reasons to use nutritional supplements when conditions warrant it, as well as some good reasons to not rely on nutritional supplements.
QUESTION: When does it make good sense to take dietary supplements?
ANSWER: When the diet does not provide adequate amounts of essential nutrients, taking nutritional supplements can be very beneficial to health. This is especially true during conditions like pregnancy and breast-feeding. While pregnant, a woman’s need for key nutrients like iron,
iodine and folic acid increases greatly, making it challenging to maintain optimal nutrition without supplementation. Normal fetal development, including brain development, is highly dependent on an adequate supply of these nutrients.
Also, since nutrient needs do not decrease along with reduced calorie intake, nutritional supplements can be important for dieters and those with low-calorie needs. As people age, total food intake generally declines, making it more challenging to meet vitamin and mineral needs without supplements or fortified foods.
Q: Are there risks to excessive use of dietary supplements?
A: Some nutrients are more risky than others. The Institute of Medicine has established “tolerable upper intake levels” for most
nutrients. These values represent maximum safe intake from food and supplements combined. So, if the level of a nutrient in a supplement exceeds this upper limit, it is clearly excessive for ongoing daily use by the average person.
Q: Can nutritional supplements help to reduce the risk for chronic diseases?
A: The scientific support for the prevention of chronic diseases like cardiovascular disease and cancer is a mixed bag. Some studies have indicated potential benefit, some no effect, and others found increased risk. For example, in a study conducted in China on 30,000 people who had a low-nutrient diet, researchers found that supplementation with a combination of beta carotene, vitamin E and selenium reduced overall cancer mortality, but not all types of cancer benefited.
In contrast, studies on Western populations found that supplementing smokers with beta-carotene substantially increased lung cancer incidence, and those who already had lung cancer died sooner than the placebo group. Other studies found that vitamin E supplementation increased prostate cancer risk, and selenium supplementation increased the risk of skin cancers.
Part of the complication with the use of nutritional supplements in the United States is that people are mixing supplements together in countless combinations. Many people are taking nutrient and herbal cocktails that are mixing chemicals together in ways never done before. The long-term effects of these nutrient blends and herbal combinations are unknown and potentially inhibit the absorption of some nutrients.
Further complicating things, some dietary supplements have been found to have labels that do not accurately express what is in the product. To check a product, the company ConsumerLab.com analyzes dietary supplements and publishes the results on its website.
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Joannie Dobbs, Ph.D., C.N.S., and Alan Titchenal, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.
