If you're being treated for high blood pressure, the condition may be tougher to control during the winter months, according to a new study by the U.S. Department of Veterans Affairs (VA).

The five-year study focused on the health records of more than 440,000 U.S. military veterans from 15 V.A.hospitals across the country. Researchers found veterans treated in the winter were less likely to see their blood pressure return to normal levels compared to those treated in the summer.

"The bottom line is that regardless of whether you're in Anchorage, Alaska or San Juan, Puerto Rico, there is a difference in high blood pressure returning to normal in the winter compared to the summer," said Dr. Ross D. Fletcher, lead researcher and chief of staff at the V.A. Medical Center in Washington, D.C., in a news release.

Researchers found a significant variation, regardless of the region or the climate,between blood pressure results during the summer and the winter.

“San Juan is virtually equal to Anchorage, as blood pressure systematically worsens in the winter and improves in the summer,” Fletcher said. “We did not see the coldest city had the biggest change in blood pressure.”

The average age of veterans in the study was 66-years-old. About 51 percent were Caucasian, 21 percent Hispanic and 27 percent black. Only 3.7 percent were female. Fletcher suggested that weight and exercise may play a role in these seasonal variations rather than southern or northern climate or the amount of light.

“There is a weight change that is significant,” Fletcher 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.”

He pointed to the importance of designing treatment strategies for patients’high blood pressure to account for seasonal variations, perhaps requiring increased anti-hypertensive intervention during the winter months.

Researchers reported the findings at the American Heart Association's Scientific Sessions taking place this week in Orlando, Florida.