There was no reason for the patients to receive vitamin D tests. They did not have osteoporosis; their bones were not cracking from a lack of the vitamin. They did not have diseases that interfere with vitamin D absorption.

Yet in a recent sample of 800,000 patients in Maine, nearly one in five had had at least one test for blood levels of the vitamin over a three-year period. More than a third got two or more tests, often to evaluate such ill-defined complaints as malaise or fatigue.

The researchers who gathered the data, Dr. Kathleen Fairfield and Kim Murray of the Maine Medical Center, were surprised. Perhaps they shouldn’t have been.

Millions of people are popping supplements in the belief that vitamin D can help turn back depression, fatigue, muscle weakness, even heart disease or cancer. In fact, there has never been widely accepted evidence that vitamin D is helpful in preventing or treating any of those conditions.