Many people with rheumatoid arthritis feel more pain and stiffness in the morning than the evening, and a new study says it could be because arthritis interferes with their circadian rhythms – the internal 24-hour body clock that affects how much sleep we get and how good it is.

In a study presented at the Annual Congress of the European League Against Rheumatism (EULAR) in Copenhagen, Denmark, scientists from Japan announced they had identified a specific genetic pathway that is responsible for an interaction between a person’s body clock and their arthritis symptoms.

“The identification of this curious pathway may help to explain the 24-hour symptom cycle seen by many patients who experience worsening of joint pain and stiffness in the mornings,” says Shunichi Shiozawa, MD, PhD, lead author of the study and chairman of The Center for Rheumatic Diseases at Kobe University Hospital in Japan.

Researchers studied 200 people living with rheumatoid arthritis (RA) from Japanese hospitals and found that sleep was significantly disturbed in more than 61 percent of them. Not surprisingly, they also found that more active a person’s arthritis was, the worse they slept.

Investigators then looked at genes in mice with arthritis and found that certain body clock genes can activate a protein that increases inflammation called tumor necrosis factor alpha, or TNF-alpha.

“The study’s basically saying when you have active RA you sleep less and wake up more,” says Rex McCallum, MD, a professor of medicine in the Division of Rheumatology at Duke University Medical Center in Durham, N.C. “People with active RA have inflammation, which causes pain and stiffness which can interfere with your sleep.”

Dr. McCallum says this study is interesting to doctors because it involves a large sample of patients and impressive data showing highly statistically significant correlations between the amount of interference with sleep and the symptoms of arthritis.

He says the message here for patients is you need to make sure you get plenty of rest and sleep when you have RA. “The two feed off each other,” he says.