Blood pressure is affected by the weather. Surveys and studies have shown that it becomes harder for blood pressure patients to keep their blood pressures in control in winter. Blood pressure generally stays higher in winter than during the hot summer days.

Hot temperatures during the summer prevent the narrowing of blood vessels. However, in winter, blood vessels constrict and this increases blood pressure because higher force is required to force blood through narrower veins or arteries. The other probable causes of higher blood pressure are weight gain and decreased physical activity in winter.

Blood pressure does not necessarily always require a steep fall in temperature. Seasonal blood pressure changes are very common in climates where temperatures change by only a few degrees during the climatic change from summer to winter. A five-year analysis of the electronic health records of 444,000 adults with high blood pressure in the United States and its nearby provinces showed that high blood pressure was less controlled in winter than in summer.

These studies give doctors the implication that it may be necessary to adjust high blood pressure medications in some people during the wintry days in order to ensure that their blood pressure levels do not rise by alarming extents.