Osteoarthritis may cause a range of depressive symptoms.
The study confirmed sleep disturbances are initially associated with depressive symptoms and pain but not disability. Over time, however, poor sleep was found to increase depressive symptoms and disability but not pain.
The findings are published in Arthritis Care and Research, a journal of the American College of Rheumatology (ACR).
"Sleep disturbance is a common complaint among those with pain, particularly among those with OA [osteoarthritis]," says study author Dr. Patricia Parmelee. "Our research is unique as we investigate the complex relationships among sleep, OA-related pain, disability and depressed mood simultaneously in a single study."
Arthritis is the most common form of disability in the US, with the Centers for Disease Control and Prevention (CDC) reporting that 1 in 5 adults (around 50 million people) have been diagnosed with the condition. OA is the most common form of arthritis, affecting an estimated 30 million Americans.
OA is characterized by pain, stiffness and problems with moving affected joints. However, previous studies have also shown that people with knee OA often report general problems with sleep (77%), including issues initiating sleep (31%) and maintaining sleep (81%).
The 'cycle of OA distress'
Recruiting participants from a variety of different sources, the researchers questioned 288 patients with knee OA about sleep disturbances, pain, disability and depressive symptoms. These patients were then followed up a year later with the same fields being measured.
The researchers conducted baseline analyses to look at the different associations between sleep disturbance and pain, disability and depression. Longitudinal analyses took the baseline sleep disturbance readings and used them to predict changes in pain, disability and depression over a 1-year period.
Sleep was found to be independently linked with pain and depression at the beginning of the study. At the baseline, disability was not associated with sleep disturbances.
Participants who reported high levels of pain had symptoms of depression exacerbated through a combination of poor sleep and pain. The participants with the strongest depressive symptoms were those who experienced both significant sleep problems and higher-than-average pain.
The researchers also found that levels of sleep disturbance at the baseline could be used to predict increases in depression and functional limitations at the 1-year follow-up. They did not, however, indicate any increases in pain over the same period.
"This study shows that depression plays a strong role in the sleep-pain connection, particularly with severe pain," says Dr. Parmelee.
Further studies needed to disrupt the cycle
The authors state that their study was limited by the inexact manner in which they measured sleep disturbance using interviews with the participants. They write that further research with a more sensitive system of measurement will be required.
Only sleep was found to be independently linked to an increase in depressive symptoms over time, and changes in pain and disability did not track with changes in depression. To the authors, this suggests that sleep could be a mediator of the relationships between pain, disability and depression.
Sleep problems increasing depressive symptoms when pain was severe was a key finding. "This has important implications for treatment, suggesting that the documented efficacy of analgesic treatment of OA-related pain in reducing sleep disturbance may help relieve pain-related emotional distress as well," write the authors.
"Further investigation of sleep in disability progression may lead to new interventions that disrupt the cycle of OA distress," suggests Dr. Parmelee. These would be gratefully received; evidence reports that rising numbers of OA cases have increased health care costs in the US by $186 billion between 1996 and 2005.
Earlier in the year, Medical News Today reported on a study that found drinking milk every day may delay knee OA in women.