People who swear they can predict the weather by the pain in their arthritic knees may be right after all, a new study suggests.

Using data from a study of U.S. adults with knee arthritis, researchers found that in general, patients’ pain flare-ups correlated with changes in temperature and barometric pressure.

The findings are published in the American Journal of Medicine.

While many arthritis sufferers feel the weather affects their pain - some say their pain increases when it’s cold or when it rains, for instance - scientific evidence of the phenomenon has been hard to find.

One problem is that, given many people’s strong convictions about the effects of weather on their pain, it’s difficult to get unbiased reports of pain flare-ups.

To get around this problem, researchers at Tufts-New England Medical Center in Boston used data from an earlier study that investigated glucosamine for knee arthritis.

The 200 adults in that study reported on their pain levels at several points over three months. The Tufts researchers took that data and compared it with meteorological information obtained from the National Oceanographic and Atmospheric Administration on the same days in each patient’s local area.

Overall, they found, patients’ pain tended to worsen when the temperature dropped or when the barometric pressure increased.

“Our data corroborate the general assertions by people with osteoarthritis that weather conditions influence their pain,” Dr. Tim McAlindon and his colleagues report.

Even the 19th century notion that arthritis sufferers fare better in climates that are warm and sunny year-round may be “partly correct,” the researchers write.

It’s not fully clear why temperature and barometric pressure might influence arthritis pain. Cold temperatures may, for instance, affect joint range of motion, or the flow of the synovial fluid that lubricates the joints, McAlindon’s team suggests.

Barometric pressure refers to the weight of the surrounding air, and it fluctuates with changes in altitude or weather. Some research, McAlindon and his colleagues note, suggests that atmospheric pressure plays a role in the stabilization of the body’s joints.

SOURCE: American Journal of Medicine, May 2007.