So-called brown fat stored on the body may prove dangerous to humans in the winter, researchers have warned.
Researchers say their findings may help explain why the rates of death from heart disease are higher in the winter months.
Professor Yihao Cao of the Karolinska Institutet, Sweden, and colleagues investigated the effects of temperature on body fat.
Brown fat is found mainly in infants but recent research has found it plays a role in the physiology of adult humans.
The researchers used a strain of mice that is genetically altered to have a predisposition towards atherosclerosis, or hardening of the arteries. As in humans, mice have white fat which stores surplus calories, and brown fat which converts white fat into heat.
This conversion of fat into heat by brown fat is activated by cold temperatures. But the researchers also found that low temperatures trigger the build-up of atherosclerotic plaque, raising the risk of heart attack and brain haemorrhage.
At the same time, cold makes the plaque more likely to rupture, causing stored fat to leak into the blood and potentially block vessels to the heart and brain. The process also leads to the build-up of low-density lipoproteins (LDL) in the blood and plaque.
Details appeared in the journal Cell Metabolism yesterday (2 July).
Professor Cao said: "At first, we thought that the cold activation of brown fat would only make the mice thinner and healthier. Instead, we found that they ended up having more fat stored in the blood vessels. This came as a surprise and was the opposite of what we thought would happen.
He added: "If this is also true for humans, it might be wise to recommend that people who suffer from cardiovascular disease should avoid exposure to the cold and to put on warm clothes when they are outside during the winter."
Dong, M. et al. Cold exposure promotes atherosclerotic plaque growth and instability via UCP1 dependent lipolysis. Cell Metabolism 2 July 2013
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