Here you are, blithely taking your vitamins, confidant that you are going to be healthier because you are going that extra distance by supplementing your diet with more vitamins than the recommended daily doses. Now there’s a report that larger doses of vitamin C may actually be clogging up the arteries you thought you were keeping open. What gives?

First, let’s start off with what vitamins actually do and why they are needed. To maintain healthy bodily functions, the body creates the nutrients it needs from the foods you consume. The chemicals and minerals the body cannot make, but nonetheless needs for health, can be loosely grouped as vitamins. Vitamins, by definition, are needed in only small amounts and often are not extensively stored in the body. Thus, they need to be consumed regularly in order not to deplete the body of these vital minerals.

Some enzyme systems in the body change the chemical makeup of cholesterol and other molecules in the body, possibly leading to processes as diverse as heart disease, cancer and even aging. Some of these possibly diseases producing chemical changes are called oxidative injury. There have been several observational studies suggesting that some vitamins, especially those that have antioxidant properties like vitamin E and vitamin C, may delay or prevent the development of hardening of the arteries. Observational studies mean that when looking at large numbers of well characterized people that have developed illnesses, there appears to be a link between some factors and the disease, but cause and effect have not yet been proved. Causality requires appropriately designed clinical trials, as discussed in a previous column. Only one clinical trial has shown a weakly beneficial effect for vitamin E. And a recent large, well-designed clinical trial showed NO benefit of vitamin E in the prevention of heart disease.

A recently reported observational study raises the disturbing possibility that patients taking 500 mg vitamin C for a year had twice the rate of thickening of the lining of the large neck arteries that feed the brain. Smokers had five times the risk. The assumption is that the neck arteries are surrogates for the other arteries in the body.

What these observations mean is that the common assumptions that larger doses of vitamins are beneficial may be flawed, since they may be based on extrapolation from inconclusive data. The fact that this is a lucrative market for vitamin manufacturers means that we are always being bombarded by commercial messages that we should view more critically until the randomized clinical trials are available to prove benefit.