Climate change may have at least one health benefit – less painful knees.
Hot days may lower the risk of knee arthritis, according to analysis based on 350,000 middle-aged men and women in the UK. The greater the number of days where the temperature was 27C or above, the lower the risk, according to research reported in BMC Public Health.
Hot weather may improve blood flow, leading to better lubrication of the joint and making it less stiff and more flexible.
Knee osteoarthritis is estimated to affect 5.4 million people in the UK. Cold weather has been associated with an increased risk of symptoms, but no research has previously looked at the effects of hot days. The researchers recruited men and women with an average age of 56 who did not have knee arthritis at the time. During the next 11 years, more than 23,000 of them were diagnosed with the condition.
Using the home addresses of the participants, the researchers calculated the number of hot days each had been exposed to in the five years before the start of the study.
A hot day was defined as having a temperature of 27C or higher. They then compared the number of hot days for those with and without knee arthritis.
Results show that those who had been exposed to the greatest number of hot days had a ten per cent lower risk of arthritis.
Moderate exercise was also found to lower the risk by seven per cent.
Knee osteoarthritis is estimated to affect 5.4 million people in the UK
Cold weather has been associated with an increased risk of symptoms, but no research has previously looked at the effects of hot days
People who experienced the most hot days and also exercised moderately found their risk reduced by 17 per cent. But excessive exercise was linked to an increased risk.
One theory is that an improved blood flow to the knees on hot days provides the joints with more oxygen and nutrients, and also helps remove any debris.
This may also improve the range of movement the knees have, say the researchers from the Vanke School of Public Health and the McGovern Institute for Brain Research, both in China.
Heat could also stimulate the release of endorphins, known as the body’s natural painkillers, and reduce the inflammation associated with arthritis.
