Widening waistlines may increase the chances of frequent, painful headaches, new research findings suggest.

In a study involving almost 31,000 adults, researchers found that compared to normal-weight people, obese individuals doubled their risk for chronic daily headache -- non-migraine attacks occurring at least 15 times per month.

"Their headache attacks were also much more severe," said study author Dr. Marcelo Bigal, director of research at the New England Center for Headache in Stamford, Conn. He was to present the findings April 14 at the American Academy of Neurology's annual meeting in Miami Beach.

In the study, Bigal and colleagues conducted phone interviews with 30,850 people who reported at least one painful headache attack over the previous year. They then compared the headache frequency and severity of underweight, normal-weight, overweight and obese individuals. Obesity was defined as a body mass index (BMI) of 30 and above (for example, a 5-foot-8 person weighing 200 pounds has a BMI of 30.4).

According to the study, 3.8 percent of individuals in the study group as a whole suffered from chronic daily headache. That prevalence rose significantly as waistlines expanded, however.

For example, 5 percent of overweight individuals -- those with BMIs between 25 and 30 -- suffered from chronic daily headache, "and if individuals were obese, that number rose to 7 percent -- almost double the average," according to Bigal, who is also an assistant neurology professor at Albert Einstein College of Medicine in New York City.

The severity of each attack increased as weight rose, too, and painful headaches also caused the obese to "miss more days of family life, social activities or work than either the overweight or people of normal weight," Bigal added. The duration of headache remained similar across the different weight categories.

Based on their findings, the researchers believe excess weight gain may be a strong risk factor for headache.

Not everyone agrees, however.

"I'm just wondering if the cart isn't before the horse here," said Dr. Seymour Diamond, executive chairman of the National Headache Foundation.

"Remember, these are people with chronic headache, who are probably more or less incapacitated by their headache," he said. "Naturally, they are not going to be doing exercise, and probably they're eating a lot, too. So, I think the obesity may be secondary to their chronic headache problem."

Bigal called that argument "reasonable," but added that what scientists know about obesity suggests it may help trigger attacks.

He pointed out that headaches, both migraine and non-migraine, are all linked to constrictions in blood vessels, often caused by inflammation.

"We know obesity per se is a cause of inflammation and is a risk factor for vascular diseases," he said. Headache is also characterized by "an inflammation of the blood vessels, so what we think is that obesity creates this pro-inflammatory state, so then you'll have more attacks."

He said his research does have some good news for the overweight and obese plagued by headache. In a second study, also to be presented at the Miami Beach conference, Bigal's team compared the treatment outcomes of 170 migraine patients.

"Our hypothesis was that it would be more difficult to treat obese migraine sufferers, but it wasn't. They responded just as well with therapy as the normal-weight patients," he said. "So it's important to deliver the message that, yes, if you're obese you will have worse headaches, but it's still possible to treat you."

Of course, the findings also suggest that one of the best ways of avoiding chronic headache may be to stay slim.

"Exercise per se improves headache, we know that," Bigal said. "Headache sufferers should watch their weight."

More information

To learn more about all forms of headache, head to the National Headache Foundation.