Dear Dr. Roach: All my life I have had severe headaches almost daily. I have been to various doctors, and none of the treatments — including medications, stress management and identifying food triggers — was effective. Doctors told me to live with it.

I have always taken vitamins. Last April, I missed my vitamins by accident, and that day I had no pain. The next day, I skipped them, and again no pain. I tried the vitamins again, and had severe headaches. No doctor ever suggested vitamins could be the cause of my headache. To the millions of headache sufferers: Try quitting vitamins! — S.A.

Answer: Millions of people take vitamins in hopes of preventing disease. There are only a few instances when taking vitamins in people with no symptoms of deficiency has definitively been shown to be beneficial. One example would be pregnant women, where the B vitamin folic acid has been shown to reduce a type of birth defect, neural tube abnormalities. Vitamin D is beneficial in older people at risk for falls or with osteoporosis. Otherwise, the studies looking at taking vitamins have generally not shown a benefit. This is probably because most people involved in such studies generally have a healthy diet. It remains debated whether vitamin supplementation is beneficial in those with a not-so-healthy diet: They probably do.

The harms of vitamins are small. I have seen a handful of cases of allergies (probably due to fillers or dyes, rather than the vitamins themselves), and headaches are well-documented, particularly from vitamin A or niacin, especially at higher doses. Some people get upset stomach or an unusual taste. Given a probable lack of benefit, it might be worth stopping vitamins for possible side effects.