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By the way, doctor: Seasonal swings in blood pressure

By the way, doctor

Seasonal swings in blood pressure

Q. My systolic blood pressure is 40 points higher in winter than in the summer (160–180 versus 120–140 mm Hg). Do the seasons affect blood pressure?

A. I’ll admit you’ve got me puzzled. Here are the possibilities I’ve come up with: Two are pretty obvious and straightforward, one’s a little far out.

First, seasonal weight gain. During the winter, especially around the holidays, people tend to eat more and exercise less than they should. The resulting weight gain causes blood pressure to rise.

Second, salt consumption. Too much salt in your diet also raises blood pressure. So, if you’re more likely — come wintertime — to be hanging around the house and raiding the refrigerator and kitchen cabinets for salty foods, that could perhaps explain the seasonal increase.

Now for the far-out idea. When a person is outside in very cold weather, the small arteries tend to clamp down, causing blood pressure to go up. The experts I talked to said that this effect would disappear soon after you went back indoors.

When I looked for research on the effects of cold temperatures on blood pressure, I found remarkably few studies — on humans. But there have been many done with mice and rats, and they show a substantial and sustained increase in blood pressure from cold temperatures. Research published in early 2005 identified two genes with a profound effect on cold-induced high blood pressure in mice. Humans have those genes too, so it’s theoretically possible that a variant of those genes is what makes your blood pressure particularly likely to go up in cold weather.

Perhaps the scientists studying the effect of cold temperatures on blood pressure in mice would be interested in studying you. If you’re interested, write us a letter or an e-mail, and we can give you their contact information.

I have one piece of practical advice: Be careful about vigorous exercise in cold weather. It could put an unusual strain on your heart.

Anthony L. Komaroff, M.D., Editor in Chief, Harvard Health Letter

Last updated:	August 21, 2006