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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."

Misbehaving nerves

Dr Vagg says the drop in pressure that often accompanies cooler weather is unlikely to cause joint pain (ABC News: Kevin Silsbury).

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.