The Body Odd - Can achy joints really predict the weather? Before the thunder rolls in or the first drop of rain falls, some people predict showers even without consulting the forecast -- they know it will rain because their joints ache. Rheumatologist Dr. William F. Harvey treats many patients suffering from some form of arthritis and almost all of them recall extra pain when it is rainy or cold. It's so common it seems everyone knows someone who predicts the weather by saying her joints throb, but it's not an old wives' tale. Weather pains exist. It's a very widely held belief. I am not sure I remember any patients who did not feel [pain during weather changes]," says Harvey, who works at Tufts Medical Center in Boston. According to the Arthritis Foundation, as many as 27 million Americans live with osteoarthritis, what's considered old-age or wear-and-tear arthritis (though there is about 100 different varieties of the condition). By 70, most people have osteoarthritis. "It is fairly well accepted that changes in weather do affect patients" joints," says Dr. Greg Deirmengian, an orthopedist at the Rothman Institute at the Jefferson University Hospital in Philadelphia. Although some people who had broken bones also complain of weather pain, Deirmengian suspects the pain originates from arthritis in adjacent joints. Researchers have attempted to study weather-related arthritis aches with varied success (they can't ask patients if they feel more pain during rain or cold because the question is leading). Harvey points to a study -- conducted by a colleague at Tufts, Dr. Timothy McAlindon, published in 2007 in the American Journal of Medicine -- that looked at barometric pressure and joint pain. McAlindon called people with osteoarthritis in their knees, asking them about their pain and how they manage it. Then he compared their pain with weather in their area during the day of the call. He found that subjects experienced more discomfort on days when barometric pressure and ambient temperature shifted, what occurs with rain. "What it showed was that changes in barometric pressure and different temperature did affect their perception of pain," Harvey says. Understanding the exact reason why this occurs puzzles doctors, but there are several theories. Most experts believe joints ache during stormy weather because atmospheric pressure changes cause additional pressure in the body. Arthritic joints, which lack enough cartilage to properly cushion them and are often surrounded by extra fluid, feel these changes more intensely than healthy joints. Also, Harvey says arthritic joints are under more pressure than healthy ones, contributing to added pain during weather changes. Studies conducted on scuba divers with arthritis show that added pressure increases pain. Harvey also notes that how blood vessels act in cold weather could contribute to pain. Blood vessels dilate, causing muscles and joints to tense and stiffen and adding to pain. Cold temperatures also could cause the fluid that lubricates joints to be less viscous, preventing joints from moving smoothly. Also, nerves could play a role, says Deirmengian. Everyone has nerves in their joints, which help them move, but arthritic joints are more sensitive. When the outside pressure changes, these already twitchy nerve endings might feel the swing more acutely. Anyone experience more arthritis discomfort during weather changes should try home remedies such as taking anti-inflammatories, icing or heating the joint, or using a brace. "Patients get flair of arthritis; ups and downs," says Deirmengian. Weather causes some of those flairs.