To Your Health

Q: I don't know how much vitamin C I should take. The government has one figure and books I have read have others. Who is right?

A: There are many different opinions about how much vitamin C (and other nutrients) to take because there is no consensus among nutrition experts about how much of the 50 or so nutrients we need each day. Over the years, recommendations have been developed by various agencies, but currently the term Recommended Dietary Intake (RDI) is used to express the amount of nutrients we need.

A little history: At the start of WWII, the government needed to know how much of the various nutrients were needed to protect our soldiers from vitamin-deficiency diseases, so the concept of Minimum Daily Requirement (MDR) arose. The MDR, as the name implies, is the smallest amount that a person's diet should supply. Later on, a "safety factor" was added to create the Recommended Daily Allowance (RDA).

Two things are very important to keep in mind: 1) These recommendations are designed to prevent deficiency diseases in an already healthy person; and 2) The numbers should never be applied to an individual.

Regarding the first fact, the number of persons in America who can be considered healthy is a minority, less than 30% of the population. Regarding fact No. 2, the RDAs do not consider individual differences and make only minor modifications for differences in life situations that profoundly affect our requirements for vitamin C and other nutrients, such as pregnancy or smoking. It is up to each of us as individuals to find our own best quantity of vitamin C to take in, as well as the amounts of other nutrients.

It is common for perceptive people to notice that their need for vitamin C varies. The amount people need depends on the season, how much sleep they get, family stress, whether they have caught a cold or other infection, or any of a number of other circumstances.

If you are confident that your diet supplies the amount of vitamin C you need, which is to say that you are in the 30% of the population that is healthy, you may not need a vitamin C supplement.

A good clinical nutritionist specializes in finding out how much of various nutrients a person needs. There are some tests for nutrient status, but these tests tend to be expensive and not entirely reliable. For instance, the amount of a nutrient in your blood does not necessarily reflect the amount you really need.

Bear in mind that the classic deficiency diseases are seldom the result of deficiency in a single nutrient. A person suffering from scurvy is likely to also be deficient in folic acid. Pellagra, which was once rampant in the rural south, resulted from both a vitamin (niacin or vitamin B3) and an amino acid (L-tryptophan) deficiency. A good multivitamin/mineral, one that is rich in antioxidants other than vitamin C, is good insurance against deficiency of several nutrients.

The RDI and similar estimates of adequate nutritional intake suffer from many shortcomings. The nutrient density of commercial animal foods often surpasses the RDI by a factor of five or more. For most nutrients, when we use more than the RDI we are not just making "expensive urine." Both research and human experience indicates that there are benefits to using food supplements. It is worthwhile to find, by experience, your own optimum nutrient intake, and it is likely to be different from the RDI.