Admissions to hospital for deep vein thrombosis and pulmonary embolism are higher in winter and lower in summer, finds a study in this week's BMJ.
Researchers in France analysed hospital admissions for deep vein thrombosis (blood clotting in the legs) and pulmonary embolism (obstruction of the main artery in the lung) between 1995 and 1998. The number of admissions per month was significantly higher in winter and lower in summer for both conditions.
Average monthly admissions for deep vein thrombosis ranged from 18% below average in August 1996 to 18% above average in February 1996 and December 1997. Similarly, average monthly admissions for pulmonary embolism ranged from 22% below average in August 1998 to 26% above average in December 1997.
It is well known that narrowing of blood vessels induced by the cold and reduced physical activity during the winter months reduce blood flow in the lower limbs, say the authors, but further work is needed to understand seasonal fluctuations in blood clotting, they conclude.