Arthritis: Does cold weather make it worse?
Many people with arthritis dread the cooler months.
In fact, some swear blind they can even predict a drop in mercury simply by the increase in swelling and pain in their joints.
But is there any truth to this notion that stiff and sore joints flare up when temperatures fall? And if so, what's causing it?
While it's a topic that's been explored in a large number of scientific studies, the results have been mixed, says Deakin University pain expert Dr Michael Vagg.
Some studies suggest a link while others do not.
"It's hard to say what's going on," he says.
The pressure factor
One aspect of cool weather that's been argued could affect joints is barometric pressure — the force exerted by the weight of the atmosphere.
Some researchers have proposed that a drop in barometric pressure, which tends to accompany cooler, damper weather, could allow tissues in joints to swell and put pressure on nerves that control pain signals.
But Dr Vagg, a clinical senior lecturer at Deakin's School of Medicine and pain specialist with Barwon Health, is somewhat sceptical.
"At extremes of barometric pressure — going to the top of Everest or diving to 50 metres — you can certainly get joint pain," he says.
"But we don't believe the minor variations in barometric pressure that you get at normal altitude [and are similar in scale to those that occur with weather changes] are actually painful.
"Otherwise you'd get sore joints from driving to the top of the Blue Mountains."
Dr Vagg says an alternative idea, with more evidence behind it, is that bodily changes triggered by cooler weather have the side effect of amplifying pain signals from joints.
Many arthritis sufferers have pain that persists, despite having joints that are not extensively damaged, he says.
One proven reason for this is that their nervous system is essentially "misbehaving"; pain signals travelling along nerves from their joint are amplified in the brain by signals carried on separate nerves called sympathetic nerves.
These sympathetic nerves are part of the body's system for maintaining its internal functioning without us having to think about it.
When it's cold, these nerves constrict blood vessels in the limbs, to minimise heat loss and help keep warm the core of the body, where vital organs are.
But the increased activation of these nerves around joints in response to cold weather might also lead to an increase in the pain a person feels, Dr Vagg argues.
"It would be difficult to study but... it's certainly more plausible than any direct effect of barometric pressure on the lining of a joint," he said.
Just get moving
But before you sell up and move to warmer climes, consider this: there's no denying a number of other things happen when the weather turns cool.
A winter drop in mood is common for many people and low mood is known to be linked to higher levels of perceived pain, Dr Vagg says.
Shorter days and cool temperatures can also make us less inclined to be active, and immobility can also make arthritis pain worse. (Among other things, it reduces the flow of nutrients and oxygen to joints.)
"I'm actually not convinced there is a definite relationship [between weather and arthritis pain] that couldn't be better explained by reduced activity and lowered mood," Dr Vagg says.
Focusing on overcoming obstacles that stop you exercising in winter rather than just blaming the weather could be a more helpful approach, he suggests. Getting active can also help overcome low mood for many people.
Ultimately, any belief your pain is linked to cold weather could be all in your mind anyway, Dr Vagg says.
The human brain has evolved to be good at identifying patterns because being able to predict events had advantages for survival.
So our brains tend to see patterns when none exists — a fact well documented by scientists. This might mean we're more likely to remember times when our pain got worse in cold weather than when it didn't.
From a practical perspective, however, it might be best to focus on what you can control.
"We can't prove one way or the other if there's a direct effect of weather on arthritis. But even if there's no direct effect, there are secondary effects likely to make pain worse, [for instance] if you have low mood or reduce activity.
"So being a bit creative about how you maintain your activity levels in winter is really good advice."