Your grandma was right all along: painful problems such as arthritis really do get worse during gloomy weather.

Although popular knowledge is very clear on this topic, there has been surprisingly little research on the influence of weather on pain. Many people would swear that their pain gets worse when it starts to rain, but then again, many people would also swear by homeopathy and astrology — folk knowledge is not always an indicator of truth.

To put that idea to the test, researchers from University of Manchester collected data from 2,500 people using smartphones. They recorded pain symptoms each day (for intervals between 1 and 15 months), while the phones recorded the weather conditions. The team found that damp and windy days increased

Cold, damp days with low pressure increased the chances of experiencing more pain than normal by about 20%. However, when taken individually, the impact of both cold and humidity was not nearly as large. It appears that the combination of cold and humid days makes things worse. It’s an innovative approach that offers an important piece of information in the study of pain.

“This would mean that, if your chances of a painful day on an average weather day were 5 in 100, they would increase to 6 in 100 on a damp and windy day,” said study author Will Dixon, professor of Digital Epidemiology, in a statement.

Since the days of the ancient Greeks, it was believed that weather can influence pain — especially joint pain. Some people even say they can predict the weather based on joint pain. That has not been thoroughly been tested, but the study brings new support for the connection between weather and pain.

However, the exact causation and mechanisms through which this process takes place remain unclear. It’s not clear whether the effect is caused by the temperature, pressure, humidity, a combination of these, or potentially something completely different. For now, this research could help develop or improve “pain forecasts”, offering new information to doctors prescribing painkillers or other drugs to patients — if the forecast is cold and wet, a stronger prescription might be justified.

“This would allow people who suffer from chronic pain to plan their activities, completing harder tasks on days predicted to have lower levels of pain,” Dixon said.

This isn’t the first study to study the connection between chronic pain and the weather. A previous 2007 study found that barometric pressure and temperature changes are independently associated with osteoarthritis knee-pain severity — but that study was only carried on 200 people, for 3 months. The evidence is not yet conclusive, but it seems to be piling up: if you’re suffering from chronic pain, check the weather forecast. It will help you make better plans.

The study, called “Cloudy with a Chance of Pain,” was funded by charity Versus Arthritis.