Multivitamin - Precautions

Precautions

The amounts of each vitamin type in multivitamin formulations are generally adapted to correlate with what is believed to result in optimal health effects in large population groups.

The health benefit of vitamins generally follows a biphasic dose-response curve, taking the shape of a bell curve, with the area in the middle being the safe-intake range and the edges representing deficiency and toxicity. For example, the Food and Drug Administration recommends that adults on a 2,000 calorie diet get between 60 and 90 milligrams of vitamin C per day. This is the middle of the bell curve. The upper limit is 2,000 milligrams per day for adults, which is considered potentially dangerous.

However, these standard amounts may not correlate what is optimal in certain subpopulations, such as in children, pregnant women and people with certain medical conditions and medication.

In particular, pregnant women should generally consult their doctors before taking any multivitamins: for example, either an excess or deficiency of vitamin A can cause birth defects. Long-term use of beta-carotene, vitamin A, and vitamin E supplements may shorten life, with the additional risk being particularly large in smokers. Many common brand supplements in the United States contain levels above the DRI/RDA amounts for some vitamins or minerals.

Severe vitamin and mineral deficiencies require medical treatment and can be very difficult to treat with common over-the-counter multivitamins. In such situations, special vitamin or mineral forms with much higher potencies are available, either as individual components or as specialized formulations.

Multivitamins in large quantities may pose a risk of an acute overdose due to the toxicity of some components, principally iron. However, in contrast to iron tablets, which can be lethal to children, toxicity from overdoses of multivitamins are very rare. There appears to be little risk to supplement users of experiencing acute side effects due to excessive intakes of micronutrients. There also are strict limits on the retinol content for vitamin A during pregnancies that are specifically addressed by prenatal formulas.

As noted in dietary guidelines from Harvard School of Public Health in 2008, multivitamins should not replace healthy eating, or make up for unhealthy eating.