High blood pressure may be more difficult to control in winter, US research suggests.
A five-year study found people treated in the summer were on average 8% more likely to see their blood pressure come down to healthy levels.
The US Department of Veterans Affairs team analysed data on 443,632 veterans treated for hypertension.
The study, reported to the American Heart Association, suggests a more active summer lifestyle may be the key.
Lead researcher Dr Ross 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."
The researchers said it was also possible that people might eat more salty foods in winter. Salt is strongly linked to raised blood pressure.
The study analysed electronic health records from 15 VA hospitals in cities throughout the US.
People with a blood pressure reading of more than 140 mm Hg systolic or more than 90 mm Hg diastolic on three separate days were identified as hypertensive.
The researchers found the same pattern emerged from each hospital they studied, regardless of whether it was based in a warm or cold climate. Locations ranged from Anchorage, Alaska to San Juan, Puerto Rico.
Dr Fletcher, chief of staff at the VA Medical Center in Washington, said people should be aware of the possibility their blood pressure may be harder to control in the winter - and be more vigilant at this time.
Professor Bryan Williams, a trustee of the Blood Pressure Association, said blood pressure was very variable - even on a minute by minute basis.
Source - BBC