Nutrients from Diet, or Supplements?

Summarized by Robert W. Griffith, MD
September 2, 2005

Introduction

Good health requires the balanced intake of certain specific nutrients in adequate amounts. During the last hundred years, essential nutrients have been identified, isolated, purified, and in some cases synthesized. This allows nutritionists to recommend people to take supplemental preparations of nutrients, to balance or compensate for possible deficiencies. The role of supplemental nutrients (vitamins, minerals, and biochemicals) has grown considerably in recent decades. But is it better try to achieve the desired balanced intakes by adjusting food intake, or by adding supplements in the form of pills or capsules?

Drs Lichtenstein and Russell of the Jean Mayer Center at Tufts University have published a review of this topic in the Journal of the American Medical Association, and we summarize their conclusions here.

Nutrient requirements

Since 1943 the US government has issued lists of the recommended daily allowances (RDAs) of nutrients, which are regularly updated as new information is gained. More recently, a new listing called dietary reference intakes (DRIs) has been issued, which contains the RDAs, estimated average requirements, and tolerable (i.e. non-toxic) upper levels of intake.

Supplementation

It was thought that some conditions - other than the obvious well-known deficiency diseases - might be prevented by ensuring sufficient intake of certain specific nutrients. Cold water has been thrown on this approach, however, by the failure of vitamin E and beta carotene to influence the occurrence of cardiovascular disease or lung cancer, as demonstrated recently in well-conducted studies. These studies examined the effects of supplementing usual diets with the two specific nutrients. Other studies have reported no benefits from supplementation with folate in trying to prevent or lessen the severity of cardiovascular disease or Alzheimer's.

Apart from disappointing effectiveness, there have been instances of harmful results of nutrient supplementation. For instance, beta carotene supplements have been reported to increase lung cancer among smokers or asbestos-exposed workers. And high intakes of folic acid may be linked to a degree of mental decline in older people, possibly because of interference with vitamin B12 metabolism (available B12 is diverted from its role in brain activity in favor of blood-making in the bone marrow).

It must also be recognized that a high intake of certain nutrients can interfere with the absorption or metabolism of other nutrients. For example, calcium inhibits iron absorption, iron inhibits zinc absorption, and vitamin E antagonizes the action of vitamin K. And high doses of alpha-tocopherol decrease plasma levels of delta- and gamma-tocopherol.

These findings mean that physicians should exercise restraint in recommending nutrient supplements, except in the case of obvious deficiency conditions.

Nutrients from foods

On the other hand, it's widely accepted that eating a healthy diet rich in the specified nutrients (as well as a whole lot of other good nutrients) is somewhat protective against several medical conditions. Hence the question posed in the title of the Tufts scientists' article.

A large number of studies demonstrate the benefits of fruit and vegetables, low-fat dairy products, and whole grains on the frequency of heart disease, high blood pressure, and cancer. The difference in the linkage of these foods and supplementation with the individual nutrients they contain can have several possible explanations. It's most likely, however, that the individual nutrients may just be 'markers' for other beneficial substances in foods, or that there are other substances in foods that are required for the specific nutrient to 'work'. Moreover, it's quite likely that not all beneficial nutrients have been identified, yet.

So, good food or supplements, or both?

For all these reasons, a shift from "rely on food to get your nutrients" to "rely on supplements to get your nutrients" would be premature at this time. As a compromise, however, it may be tempting to regard taking supplements as an insurance policy to ensure optimal nutrient intake.

There are several reasons why taking supplements as an 'insurance' is not a good idea. First, the supplement-taker might well feel it no longer necessary to eat a healthy diet. Second, a number of common foods are already enriched with different nutrients - cereals, bread, milk. Adding supplemental nutrients might bring the total level into the toxic range. A recent report on increased hip fractures in postmenopausal women taking vitamin A demonstrates this risk.

Targeted supplementation?

The authors of this article do not recommend a change in health policy from one with the emphasis on food and diet to one that emphasizes nutrient supplements. However, they do see room for targeted supplementation in certain segments of the population - e.g. folate for pregnant women to reduce risks to the baby, and calcium and vitamin D in elderly people to help them reach the RDAs. They offer hope that, as our knowledge of the role nutrients play increases, we shall be able to improve the use of supplements in a targeted fashion to achieve even better results.

Source

• Essential nutrients: food or supplements? Where should the emphasis be? AH. Lichtenstein, RM. Russell, JAMA, 2005, vol. 294, pp. 351--358

Related Links
Food and Nutrition Information Center: DRIs and RDAs
Unexpectedly, Extra Folate is Unhelpful in Older People
Vitamin E and Alzheimer's
Serum Iron Levels are Linked to the Metabolic Syndrome