Greater blood clot risk for heavier middle-aged women, especially after surgery

A major study by researchers from the Universities of Otago and Oxford has found that overweight and obese middle-aged women are at much higher risk of developing potentially fatal blood clots than women who are a healthy weight.

In what is the largest study of its kind, researchers linked questionnaire data from a cohort of more than one million UK women with their hospital admission and death records to examine the risk of venous thromboembolism (VTE) in relation to body mass index (BMI), both without recent surgery and in the first 12 weeks following day or inpatient surgery.

VTE is a relatively rare but potentially life-threatening condition involving blood clots in the legs (deep vein thrombosis or DVT) which sometimes break off and travel to the lungs (pulmonary embolism).

The research is published in this week’s edition of the US journal Circulation. The lead author of the paper, Dr Lianne Parkin from the Department of Preventive and Social Medicine at the University of Otago, says the research followed up members of the UK’s Million Women Study for an average of six years. The women’s average age was 56 when they were recruited into the study.

Dr Parkin says the findings show that both overweight and obese women are generally at higher risk of VTE compared to women of a healthy weight, with their risk increasing progressively with increasing BMI and rising sharply following surgery.

“Surgery is known to increase the risk of VTE and our research shows that the risk of post-operative VTE is higher in women who are overweight or obese than it is in women who are a healthy weight”.

In the 12 weeks following inpatient surgery, the researchers calculated that 4.8 in 1000 women with a healthy BMI (less than 25) were hospitalised or died from VTE, compared with 7.0 in 1000 for those who were overweight or obese.

“We also found that women who were overweight or obese were more likely to undergo surgery than those in a healthy weight range,” Dr Parkin says. “So heavier women are more likely to have surgery, and they are more likely to develop blood clots following that surgery.”

More generally, the findings suggest that avoiding weight gain and even small weight reductions are likely to reduce the risk of VTE in middle-aged women, Dr Parkin says.

“Of course keeping to a healthier weight not only reduces VTE risk, it also reduces the risk of other more common conditions such as heart disease and diabetes.”