A study conducted by researchers from the U. S. Department of Veterans Affairs found that veterans treated for hypertension had different reactions, varying with the season.

A team of researchers form the U. S. Department of Veterans Affairs analyzed data from 443,632 U. S. military veterans treated for hypertension. Some were treated during the summer while others during winter. Their electronic health records from 15 VA hospitals in cities throughout the U. S., reports BBC News.

The five-year study was presented to an American Heart Association meeting. Its authors found that patients treated in the summer were on average 8% more likely to see their blood pressure come down to healthy levels.

A possible explanation for this is that people tend to be more active during the summertime. Lead researcher Dr Ross Fletcher, a researcher with the Department and chief of staff at the VA Medical Center in Washington, said: “People gain weight in the winter and lose weight in the summer. People tend to exercise more in the summer and less in the winter,” as quoted by BBC News.

The researchers said it was also possible that people might eat more salty foods in winter and salt is known to raise blood pressure.

Fletcher told Reuters in an interview: “We are seeing seasonal variation in all of the cities.” He noted that about 60 percent of the patients had a marked change in blood pressure control in the winter.

Fletcher added that he and his team had taken into consideration the possibility of the blood pressure increase to be due to the changes in temperature or daylight that occur in the winter or to the latitude of the city, but that they eventually ruled this out.

The authors concluded that weight gain, different eating habits and less exercise during winter were the more likely factors leading to an increase in blood pressure.

Fletcher said people should be more careful during winter months and try to prevent hypertension by avoiding foods rich in salt and by exercising. “It does appear that if one wants to have very tight control of blood pressure, that the 'winter dip' in control should be addressed, if not by a change of lifestyle, perhaps even by a change of medication,” he told Reuters.

High blood pressure – hypertension - can lead to such major health problems as stroke, heart failure, heart attack and kidney failure.