Many women have believed this for years, but research now confirms it: Stress can cause painful periods.

Women who are stressed have double the risk of painful periods than women without a lot of stress, according to a study first published last year in Occupational and Environmental Medicine .

"Stress has been linked to a variety of other [adverse] health outcomes," study author Dr. Xiaobin Wang, a pediatrician at Children Memorial Hospital in Chicago , told HealthDay . But she said she believed the study was the first to find an association between painful menstruation and stress.

For Wang's study, 388 healthy women between the ages of 20 and 34 were asked to keep daily diaries for up to 12 months. Many of the women -- all textile workers in China -- were newly married, none had children, but all hoped to become pregnant. In the diaries, the women recorded their stress levels as low, medium or high, and kept track of their menstrual cycles as well as any pain during their periods. They also supplied demographic information and information about the use of birth control pills.

Women who had painful periods were most likely to report medium or high levels of stress, according to the study. Of the women with high stress, 44 percent reported having painful periods, compared with 22 percent of those who said they had low stress.

There's often no known cause for menstrual pain in young women, according to the National Women's Health Information Center . In older women, painful periods may be a sign of fibroids or endometriosis.

How stress might cause painful periods is not known, and Wang said that issue was beyond the scope of her study.

"We can only speculate," she said. "Stress can affect hormone levels -- for example, progesterone and prostaglandins."

The hormonal theory makes sense, said Dr. William Growdon, chairman of obstetrics and gynecology at Santa Monica UCLA Medical Center .

"Prostaglandins are potent stimulators of smooth muscle contraction," he told HealthDay , adding that higher levels could translate into more menstrual cramping.

Taking nonsteroidal anti-inflammatory drugs (NSAIDs), such as Advil or Aleve, can reduce the levels of prostaglandins, Growdon said, as can taking birth control pills.

But controlling stress, he said, is harder. "It's hard to write a prescription for stress reduction," he said.

Growdon said that other researchers have looked at this issue and did not find a connection between stress and period pain.

"Different people have different responses to stress," he said. "People have different tolerances for pain."