Shock of cold may offer therapeutic benefits

HARVARD HEALTH LETTER

Winter and its chilly temperatures are a mixed blessing when it comes to human health.

Although it's a bit theoretical, cold weather may help you slim down by stimulating metabolically active brown fat. And in Scandinavia and Russia, many people actively seek out the cold: Wintertime swimming in frigid water is believed to do health wonders, and there's some science (not much, but some) suggesting it might be so.

Most of us spend the winter trying to stay warm and avoid getting cold, but a little bit of exposure could be good because it trains blood vessels in the skin to be responsive. Brown fat is the heat-producing, calorie-burning fat that babies need to regulate body temperature. Most of it disappears with age, but PET scans have shown that adults retain some brown fat. Years ago, Finnish researchers reported that outdoor workers had MINUS 166 DEGREESUsing cold temperatures for medical purposes is taken quite seriously in other countries. "Whole-body cryotherapy" was developed in Japan to treat pain and inflammation from rheumatic and other conditions. Patients spend one to three minutes in a room cooled to -166 degrees.

Several years ago, Finnish researchers reported the results of a study of 10 women who for three months took cold-water plunges (20 seconds in water just above freezing) and submitted to whole-body cryotherapy sessions. Blood tests were unremarkable except for a two- to threefold jump in norepinephrine levels minutes after cold exposure. Norepinephrine is a chemical in the nervous system that plays a role in pain suppression.

But before taking a polar bear plunge, you may want to think about the toll cold and winter take.

IT'S NOT ALL GOOD NEWSCold weather and respiratory disease, including flu, go hand in hand. Research has shown that cold spells are reliably followed by upticks in the number of deaths from respiratory disease. Some of this may have to do with a few infectious organisms, like flu viruses, thriving in colder temperatures, but there's also evidence that exposure to cold temperatures suppresses the immune system, so the opportunities for infection increase.

A study in The New England Journal of Medicine in the late 1970s famously debunked the belief that the common cold is linked to cold exposure, but British researchers have maintained that there is a cold-to-common cold connection. Their hypothesis: Cold air rushing into the nasal passages makes infections more probable by diminishing the local immune response there.