Your joints probably aren't achy just because it's raining, study finds

That creak in your knee probably doesn’t get worse on rainy days, even if you notice it more when the skies turn grey.

That’s the conclusion of a study from Harvard Medical School that finds people who go to the doctor on rainy days don’t complain any more about joint pain than people who check in on sunny ones.

People have connected weather to health going back to ancient Greece. In a 2014 study of arthritis patients from six European countries, researchers found that 67% believed their joint pain was affected by the weather. Women, more anxious people, and people from Southern — rather than Northern — Europe were more likely to associate the two, the survey showed.

But most scientific examinations find no link between weather and joint pain.

In the latest study, researchers looked at insurance claims from more than 11.5 million doctor’s visits by patients over 65. Researchers then connected the medical complaints from these visits to daily rainfall totals from National Oceanic and Atmospheric Administration weather stations near the doctor’s office.

Harvard Medical School's Anupam Jena, who led the study, said that if joint or back pain were truly connected to bad weather, people visiting their doctors on rainy days would complain about aching knees or backs, even if their appointment was scheduled for another reason.

“If this is really something that happens, we should be able to see it in large enough data (sets) like this,” said Jena, who is also an internist at Massachusetts General Hospital.

But they didn’t.

So why does this association persist? Researchers suggest a few possibilities.

It’s tough to prove a negative, so there may be a true association that studies simply haven’t picked up, said Donald Redelmeier, a professor of medicine at the University of Toronto in Canada, who was not involved in the study, but came to a similar conclusion in 1996.

“If there is an association between changes in the weather and flairs of arthritis pain, it is small,” he said. “If someone moves to Arizona hoping it’s going to relieve all their joint problems, they’re going to be disappointed.”

Redelmeier thinks the real reason we make a connection is that it fits our intuition. We watch the rain pour down on houses, cars and other objects. We call things “weather-beaten” after they’ve been outside for a while. So why shouldn’t the rain take a toll on us?

It’s also easy to turn a single day of bad weather and joint pain into a solid belief, Redelmeier said.

"We scrutinize all subsequent experiences in a slanted manner,” he said. “It’s extremely easy to see patterns even when none exist.”

Once we have the association in our minds, we notice when we have joint pain and it’s raining, but fail to reflect on the weather when we have pain on sunny days, Jena added.

There is also a plausible biological explanation for thinking that bad weather is bad for our joints, according to E.J. Timmermans, a post-doctoral researcher at the Amsterdam Public Health research institute, who was not involved in the study but conducted the 2014 one in six European countries.

“Humidity and temperature may have an effect on the expansion and contraction of different tissues in the joint, resulting in pain at sites of microtrauma,” he said. Low temperatures may make the fluid in joints thicker, “thereby making joints stiffer and perhaps more sensitive to the pain of mechanical stresses.”

Redelmeier said there is a danger in believing medical myths. If we think humidity is causing our joint pain, we might spend money on a costly dehumidifier, “which is a step in the wrong direction,” he said. The real answer to reducing joint pain is probably much cheaper and simpler, he said: regular exercise and weight control.