Weather influences people's joint pain -- but not in the way you might expect. New research looking at Google searches about joint pain found that, as temperatures rose within the study's focus span of 23 degrees to 86 degrees Fahrenheit (minus 5 to 30 degrees Celsius), searches about knee and hip pain also increased steadily.
Knee-pain searches peaked at 73 degrees F (23 degrees C) and were less frequent at higher temperatures, while hip-pain searches peaked at 83 degrees F (28 degrees C) and then tailed off.
Interestingly, while some people say that their joint pain gets worse when it's raining, the analysis showed that rain actually reduced search volumes for both knee and hip pain.
According to the researchers from the University of Washington School of Medicine (UW Medicine) and Harvard University, the findings indicate that people's activity level -- increasing as temperatures rise, to a point -- is more likely than the weather itself to cause pain that spurs online searches.
The study used Google Trends to analyse five years of Google searches for hip pain, knee pain and arthritis, as well as a control search related to stomach pain, in 45 cities across the United States.
The reason for using internet data is that web searches are increasingly people's first response to experiencing adverse health symptoms.
"We were surprised by how consistent the results were throughout the range of temperatures in cities across the country," said Scott Telfer, a UW Medicine researcher in orthopaedics and sports medicine. He conducted the study with Nick Obradovich, a postdoctoral fellow in science, technology and public policy at Harvard.
The local weather data included temperature, precipitation, relative humidity and barometric pressure, but the results showed that only temperature and precipitation had statistically significant associations, and only with searches for knee and hip pain.
Because these searches increased as temperatures rose until it grew uncomfortably hot, and rainy days tended to slightly reduce search volumes for hip and knee pain, the researchers inferred that "changes in physical activity levels" were primarily responsible for those searches.
"We haven't found any direct mechanism that links ambient temperature with pain," Telfer said. "What we think is [a] much more likely explanation is the fact that people are more active on nice days, so more prone to have overuse and acute injuries from that and to search online for relevant information. That's our hypothesis for what we'll explore next."
The findings of the study have been published in the journal PLOS ONE.