The quintessential canadian conversation topic – weather – might get a lot more interesting now that science is researching its impact on certain health conditions.

The latest research, conducted by scientists from Yale University, Duke University and Harvard University, compared the stroke records of millions of Americans with climate trends. The study found that extreme cold, high humidity and dramatic daily temperature swings translated into a higher chance of having a stroke.

Although this issue has been examined before, this is the largest study on record, cross-referencing stroke hospitalizations with weather patterns in 46 U.S. states over a two-year period. In general, those at risk for stroke are more likely to suffer one in the winter months, although there’s also a peak in July.

Patrice Lindsay, director of best practices and performance at the Heart and Stroke Foundation of Canada in Toronto (HSF), says these findings are interesting and tie into what those in the field have long suspected anecdotally. But she cautions Canadians not to take the study too literally: “It doesn’t mean that every time it snows or it’s freezing cold, people are going to have a stroke.”

Canadians who have common risk factors for a stroke – individuals with high blood pressure, who smoke, who are overweight and don’t exercise – are more likely to suffer a stroke under certain weather conditions, she says.

Extreme cold, high humidity or sudden dips and climbs in temperature – a typical Canadian winter, in other words – puts stress on the body, which exacerbates the chance of stroke for those who are already at risk, Lindsay says: “It’s fourth or fifth on the chain.”

Lindsay compares these weather events to the risk of thrombosis – blood clots in veins that can lead to a stroke – for those taking a long plane flight. Not everyone is able to walk around during a long flight to prevent clotting, she says, but that doesn’t mean everyone is at risk of a stroke.

Although the research is compelling, the study doesn’t carry the scientific methodology necessary for it to be included on HSF communications material.

But, Lindsay says, she would share the information with friends and family who already bear some risk of having a stroke. Also, she adds, much like sodium intake (avoid salt and processed foods, and your sodium levels will drop), avoiding the risk is fairly simple. On days in which the weather is extremely cold, very humid or changing dramatically, Canadians with underlying problems, such as high blood pressure, should try to stay inside and avoid putting that extra stress on their bodies.

People with other health conditions aren’t so lucky when it comes to weather’s impact on their health. It’s long been a claim of arthritis sufferers that humidity brings on flare-ups. However, recent research indicates that there’s more to the arthritis weather issue than humidity. A study released in February by Dutch researchers found that not only does humidity increase pain levels for those with arthritis, but barometric pressure also plays a significant role in pain.

That study found that for every 10-hectopascal rise in air pressure (or a 10% rise in humidity), self-reported pain and joint stiffness by osteoarthritis patients rose by one point on a scale of 100. Using this accepted pain model against typical weather patterns, changes in air pressure and humidity can result in pain increases of five or six points.

Although that may not seem like much – the accepted approach is that the pain scale has to increase by 10 points to be considered statistically viable – this doesn’t mean it’s not felt acutely by those who suffer from arthritis, says Irene Rand, physiotherapist and regional clinical director with the Arthritis Society Burlington, Ont.: “I see people all the time who are affected by weather.”

Weather doesn’t usually cause major flare-ups, Rand adds, but it does increase pain, swelling and general malaise enough that patients often boast they could choose a second career as a weather broadcaster.

But what’s unusual about arthritis, she says, is that not everyone is affected the same way. Some patients experience pain and swelling a few days before a weather change; others on the days themselves. While avoiding humidity is possible (stay in air-conditioned areas), patients are out of luck when it comes to changes in barometric pressure and their impact on the joints. So, sufferers should take it easier on those days.

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