If your child complains of chronic headaches, you might want to check his or her sleeping habits, according to a new study.

Researchers at the Mayo Clinic in Rochester, Minn., found that children who have frequent headaches are more likely to have sleep problems.

The study included 100 children ages 6 to 17 who had chronic headaches -- which was defined as having a headache 15 or more days a month for three months or more.

They found that more than two-thirds of children studied who suffer from chronic daily headaches also experience sleep disturbance, especially trouble getting to sleep. For children with episodic headaches, one-fifth had sleep problems.

"The number of patients who have headaches and also sleep disturbance surprised us," said Dr. Kenneth Mack, a pediatric neurologist specializing in headache and one of the study's researchers. "They also have the same sleep disturbance: a delay in sleep onset."

In addition to having trouble getting to sleep, sleep problems found in the study included awakening during the night or too early in the morning, or not feeling refreshed after sleep.

The findings were presented this week at a sleep disorders conference in Rancho Mirage, Calif.

Teens are at the highest risk for headaches, which might be due to higher stress levels and sleep shortages. Mack said a typical teen needs about 9.5 hours of sleep per night -- more than most teens get.

But the researchers don't know which problem comes first -- sleep problems or headaches.

"They feed on each other: Sleep problems make the headaches worse, and the headaches make the sleep problems worse," Mack said. "Also, the worse the headaches, the more likely children are to have sleep problems, and vice versa. They could have a common cause, or one problem could be an early sign of the other."

The researchers said doctors should treat children for both problems simultaneously. Drug-free treatments may include paying attention to maintaining a routine in the child's schedule and developing good sleep hygiene. Medications are also available to help both problems.

About 10 to 20 percent of children have episodic headaches. Chronic daily headaches occur in up to 4 percent of girls and up to 2 percent of boys.