People with advanced degrees and women more than men are likely to suffer tension headaches, according to a new study.

The study, based on a survey of more than 13,000 people, estimates that nearly two out of five people in the country experience at least one tension headache in the course of a year. But people with graduate school educations had the highest rates, 48.9 percent for women and 48.5 percent for men.The research, was conducted by Dr. Brian Schwartz and colleagues at the Johns Hopkins School of Public Health. The report was published in The Journal of the American Medical Association.

Women were 15 percent more likely than men to suffer from tension headaches across all age, racial and educational groups. People in their 30s had the highest prevalence of any age group, 46.9 percent for women, 42.3 percent for men.

Schwartz said the survey doesn't explain why education and sex should make such a difference, but speculated that "work-related factors may have a role."