Do daily vitamins help you or hurt you?

DEAR DOCTOR K:

I’m a 35-year-old woman who has taken vitamin pills since I was a girl. Some people tell me they don’t help, and may even hurt me. What’s the truth?

DEAR READER:

I’ll never pretend to tell you the “truth” in this column, because I don’t always know what it is. And I’ve seen what people considered to be the truth change. But I will give you my best current assessment of what scientific studies show.

First of all, there’s no question that you need vitamins. In fact, they are substances all of us need to live. In developing nations, many people are made very sick and even die because of severe vitamin deficiencies.

Most of us in developed nations, however, get most of the vitamins we need in our diet — even if we’re not always eating a perfectly balanced diet. Many of today’s foods are fortified with vitamins.

Let me begin by listing the two vitamins that I think many people need to take. First, women like you who are of childbearing age should take a folic acid (or folate) pill (400 micrograms daily) to protect against birth defects in their babies, should they get pregnant. Large scientific studies have proven the value of taking this vitamin.

The other vitamin to consider is vitamin D. Based on current evidence from scientific studies, many experts recommend that older adults take a vitamin D pill every day. Opinions vary as to the amount, but I would recommend 1,000 International Units of vitamin D3 every day to people age 60 and over. People of any age with low blood levels of vitamin D, or with bone diseases like osteoporosis, also should take vitamin D.

Large studies are underway to see if other people could benefit from daily vitamin D pills, as well. I’m betting that the studies will show such a benefit, but I could be wrong. That’s why we do studies: Facts matter a lot more than opinions.

There are risks to taking vitamin pills in high doses. For example, high doses of vitamin A can increase the risk for osteoporosis. Beta carotene pills, a form of vitamin A, can increase the risk of lung cancer in people at high risk, such as smokers. High-dose vitamin C can cause kidney stones.

Some people in the United States and other developed nations are at risk for vitamin deficiency diseases. This includes alcoholics, poor people with poor nutrition, people with diseases that impair their digestion (like Crohn’s disease) or vegans who are at risk for vitamin B12 deficiency.

What about taking a multivitamin pill each day? There is little evidence that it either helps you or hurts you. They’re not very expensive, and they’re an easy way to fill any nutritional gaps. If you do decide to take a multivitamin, look for a brand that contains enough vitamin D.

Finally, because you are a young woman, don’t forget my advice about the daily folic acid pill. It’s very important, even if you don’t intend to become pregnant: Sometimes pregnancy is an unintended surprise.

(This column is an update of one that ran originally in December 2011.)