It's harder for people to control their blood pressure in winter, according to experts. A study reported at the American Heart Association meeting describes the result of an analysis of the vast US Veterans Administration database. The health records of almost 1.2 million patients from 15 VA hospitals were examined. Half of them were white, one in four were black, and one in five Hispanic. Their average age was 66.

In the total collective, there were 444,000 patients with high blood pressure. There was a significant variation in every city, warmer or colder, in return to normal blood pressure in winter compared to summer. The average significant difference in percent of patients returning to normal was 7.8% between the two seasons, based on patients' blood pressure readings.

Why is it harder to control blood pressure in the winter ? "There's a weight change that is significant," said one of the investigators. "People gain weight in the winter and lose weight in the summer. [And] people tend to exercise more in the summer and less in the winter."

Another expert proposed that the cold played a role. In a cold atmosphere, vasoconstriction (narrowing of the blood vessels) occurs, and blood pressure goes up a small amount. Cold medicines can have a similar effect. And depression, which is commoner in the winter, leads to more alcohol and coffee consumption, also increasing vasoconstriction.

Whatever the mechanism, accept the findings, and take more care to control your hypertension in the winter - it's worth the effort. Or get a dog.