Having sleep problems in addition to osteoarthritis may lead to greater disability over time, according to a new study.

“If your pain is keeping you awake today, you’re at risk of functional decline in the future,” said lead author Patricia A. Parmelee of the Center for Mental Health and Aging at The University of Alabama in Tuscaloosa.

But these are very preliminary results, she added, noting that her team is among the first to examine how pain, sleep and mental health symptoms interact over time.

Almost 15 percent of U.S. adults over age 35 have some form of osteoarthritis, joint pain due to wear and tear on cartilage, according to the Centers for Disease Control and Prevention. Previous studies have found that having arthritis increases the likelihood of sleep problems as well.

But it’s been unclear which comes first and what role mood plays in both pain and sleep problems.

For the new study, the researchers mailed questionnaires on sleep disturbances, pain, functional limitations and depression symptoms to 367 adults with diagnosed knee arthritis.

During follow-up diagnostic interviews, participants discussed trouble falling asleep, waking frequently in the night or waking too early in the morning. About 70 percent of people in the study reported some form of sleep disturbance.

For physical function, participants rated their mobility, ability to walk and bend, hand and finger function, arm function, self-care and ability to do household tasks.

Those with sleep problems were more likely to have symptoms of depression and tended to have worse pain compared to people without sleep problems, but sleep was not linked to functional disability.

Especially for those with more severe knee pain, sleep problems were linked to worse depression symptoms, according to the results in Arthritis Care and Research.

When 288 participants answered the same questions a year later, those who had previously reported sleep disturbance were more likely to report an increase in depression and functional disability.

At any given moment, the results showed that “the combination of sleep and pain puts depression through the roof,” Parmelee told Reuters Health. Over time, “sleep disturbance predicts increased depression and increased disability.”

“A lot of people would expect that the sleep problems would result in more pain,” which didn’t seem to happen in this study, said Kelli Allen, associate director at the Center for Health Services Research in Primary Care at the Durham VA Medical Center in North Carolina.

“But there’s some relationship directly between pain and downstream disability,” she told Reuters Health.

The measure of sleep conditions was very broad, Parmelee said, which might explain why sleep disturbance wasn’t linked to an increase in pain. Self-reported sleep problems and objectively measured sleep problems don’t always line up, she said.

In any case, there should be more emphasis on the importance of screening for sleep problems, particularly for people with arthritis, said Allen, who was not part of the new study.

Some medications treat both sleep and depression, while some help with pain and depression, but medications are not the only options, she said.

Physical activity is known to improve pain levels and sleep quality and to reduce depression risk, Allen said. Cognitive behavioral therapy may also address multiple dimensions of osteoarthritis symptoms.

“We do need to intervene as much as possible because sleep problems put people at risk of depression and disability,” Parmelee said.

Two decades ago when she started studying osteoarthritis, people thought disturbed sleep was just something patients had to learn to live with, but that attitude has changed recently, Parmelee said.

“Very often in talking with people about this, some folks don’t put that much emphasis on the importance of sleep and don’t understand that in the long range it can be important,” Parmelee said. “If you’re having sleep problems you need to get help for that.”