Vitamin D deficiency may account for frequent headache.

Men who have low levels of vitamin D may be at increased risk for frequent headaches, a new study from Finland suggests.

The study analyzed information from about 2,600 Finnish men ages 42 to 60 who gave blood samples and answered questions about the frequency of their headaches. The men were originally part of a study on risk factors for heart disease, and were assessed in the years 1984 to 1989.

Nearly 70 percent of the men in the study had blood vitamin D levels below 20 nanograms per milliliter (50 nanomoles per liter), which is generally considered the threshold for vitamin D deficiency. Low vitamin D levels are a particular concern in Finland and other Nordic countries, because these countries are farther north and have less exposure to sunlight, which the body needs to make vitamin D, the researchers said. [9 Good Sources of Disease-Fighter Vitamin D]

On average, men with frequent headaches — occurring at least once a week — had vitamin D levels of 15.3 ng/ml (38.3 nmol/L), compared to 17.6 ng/ml (43.9 nmol/L) among those men without frequent headaches. (In the United States, vitamin D levels are usually reported in ng/ml, while in other parts of the world, they are reported in nmol/L.)

Men with the lowest vitamin D levels (below 11.6 ng/ml or 28.9 nmol/L) were about twice as likely to have frequent headaches, compared to men with the highest vitamin D levels (above 22 ng/ml or 55 nmol/L.)

The study adds to a growing body of evidence linking low vitamin D levels to an increased risk of certain diseases and conditions, including headaches. The new study is one of the largest to look at the link between vitamin D and headaches, the researchers said.

However, the study was conducted at a single point in time, so the researchers cannot tell which came first, the low vitamin D levels or headaches, the scientists said. It's possible that people with frequent headaches may be less likely to spend time outside, and so they have less exposure to sunlight, the researchers said. However, this explanation may be less likely in Finland, where people overall have less exposure to sunlight, the researchers said.

In addition, because the study involved only men, it's not clear if the findings also apply to women, the scientists said.

Future studies are needed to see if vitamin D supplements may prevent or treat frequent headaches, the researchers said. The study was published online on January 3 in the journal Scientific Reports.