"Among people with arthritis, the prevalence of sleep disturbances was very high - about 23%, or more than 10 million Americans," said Dr. Grant Louie, now at Johns Hopkins University Medical School in Baltimore, Maryland.
In people without arthritis, by comparison, the rate of sleep disturbances was only about 16%.
Louis headed up the study when he was still at the National Institutes of Health. He and his colleagues wanted a better understanding of the association between arthritis and sleep problems than previous small studies provided.
They analysed health data from 23,134 adults, age 18 or older, gathered in the large 2007 National Health Interview Survey. Participants provided information about a wide range of topics including smoking, alcohol consumption, diet, exercise, weight, sleep, and chronic health problems.
Overall, nearly 20% of the study participants said they'd been diagnosed with arthritis.
There are two types of arthritis, inflammatory and non-inflammatory. The most common is non-inflammatory osteoarthritis - a breakdown of joint cartilage - which is caused by injury, ageing, or other causes.
In the current study, however, the researchers did not distinguish between the two.
Compared to people without arthritis, people with arthritis were almost three times more likely to report one or more sleep problems: not being able to fall asleep (insomnia), excessive sleepiness during the day, or sleeping less than six hours.
Other health problems
Sleep problems have been associated with other health conditions such as acid reflux, obesity, diabetes, and heart disease, so the researchers next took patients' other illnesses into account.
They found that even with other medical problems, those with arthritis were still more likely to suffer from sleep problems compared to those without arthritis - although the connection wasn't as strong as before.
Most of the sleeping problems were related to pain and joint mobility limitations, according to the investigators.
In other words, pain and joint mobility problems were better predictors of trouble sleeping compared to just having a diagnosis of arthritis, they report in the journal Arthritis Care and Research.
Rate of sleep disturbances
Even more striking, Louie said, was the rate of sleep disturbances in arthritis patients who said that in the past year they'd had problems with depression and anxiety. Louie called these problems "often neglected symptoms."
"Depression and anxiety were the most important factors identifying" which arthritis patients would have all three sleep disorders (insomnia, sleepiness during the day, and less than six hours of sleep), he said.
Arthritis patients with upper gastrointestinal problems (such as ulcers, acid reflux, or heartburn) were also particularly vulnerable to sleep problems, a fact with implications for how pain symptoms are treated.
That's because "many medications used for arthritis pain relief can have upper GI symptoms as adverse effects," the researchers point out.
They conclude that their study results reinforce the findings of previous research and underline the need for doctors to ask arthritis patients about sleep problems, "especially those reporting pain or with depression or anxiety," and to treat them appropriately.
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