Dietary supplements help fill gaps, but use caution

There is a great deal of scientific controversy about whether taking vitamin and/or mineral supplements is beneficial. Some studies indicate there is no evidence that supplements benefit health and that supplements may even harm health. Other studies indicate that dietary supplements can help to provide essential nutrients that are commonly low in contemporary diets.

Multiple studies show that many Americans are not meeting the recommended intakes of at least one essential nutrient and that a multivitamin/mineral supplement can make up for inadequate intake for a few cents a day.

QUESTION: Why is there controversy about the benefits of vitamin and mineral supplements?

ANSWER: There are two main reasons for the controversy. First, if individuals have an adequate dietary intake of essential vitamins and minerals, then they would not be expected to benefit from a supplement. More than enough of a nutrient is not necessarily better or even safe. Those, however, who are consuming inadequate amounts of any essential nutrient will benefit from a supplement.

Because many nutrient supplement studies are based on large groups of people over time, it is rarely possible to determine whether participants are meeting their nutrient needs from foods. Consequently, any supplement benefit to deficient individuals can be lost in the context of a large research study that primarily consists of people meeting their nutrient needs to start with.

Second, dietary supplements are not created equal. Because some nutrients interfere with the absorption of others, the supplement formulation is critical to its effectiveness. For example, calcium inhibits the absorption of iron and zinc. If a women’s supplement has high amounts of calcium, they might absorb very little of the iron and zinc as compared with a pill with no calcium.

Q: Who might benefit from taking supplements?

A: In general, people who consume diets limited in specific food groups are the most likely to need supplements. This can include people who exclude or consume limited amounts of foods like milk products, lean meats, fish, or fruits and vegetables.

Also, people who are restricting calories and older people who consume very low-calorie diets generally do not meet their nutrient needs from the food they eat. Supplements or properly fortified food can help to fill the nutrient gaps for these people.

It is important to understand that an inadequate intake of an essential nutrient typically will not have a noticeable effect on the body for several months or even years for some nutrients. Therefore, diet changes that eliminate a food group or decrease food variety might initially seem to be beneficial but could cause damage to health in the long run.

Q: If you don’t need a supplement, are there issues with taking one anyway?

A: Even nutrients can be toxic in excess. The Institute of Medicine has established upper limits for the intake of nutrients most likely to cause problems when consumed in excessive amounts for too long. For most nutrients it takes months or years of excessive intake for noticeable problems to manifest. Nutrients of most concern include vitamins A, B-6, and D as well as calcium, iron, zinc, selenium and copper.

Overall, there is little or no controversy that the ideal way to meet nutrient needs is by eating a reasonable variety and quantity of wholesome food. When this isn’t done or can’t be done, supplementation can be a way to meet nutrient needs.

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, 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.