Study finds bariatric surgery linked to substantially lower risk of blood clots long-term

Largest study to date helps patients weigh risks and benefits of surgery

New research suggests that people with severe obesity who have bariatric surgery have a substantially lower long-term risk of blood clots in veins (venous thromboembolism) than those who don’t have the surgery.

The study, led by Kaiser Permanente Washington Health Research Institute (KPWHRI), was published in Obesity Surgery. It is the first U.S. study and the largest study to date to address long-term risk of venous thromboembolism (VTE) in a population of adults with severe obesity who underwent bariatric surgery.

“We wanted to provide evidence to patients considering whether or not to proceed with bariatric surgery as a treatment for severe obesity,” said Laura B. Harrington, PhD, MPH, lead author of the study and an assistant investigator at KPWHRI. “Having a clearer understanding of the risks and benefits, both short-term and long-term, hopefully will help people talking with their doctor about surgery make a decision that feels good to them.”

The study followed adults with severe obesity in 3 different Kaiser Permanente regions for an average of 9 years. More than 30,000 bariatric surgery patients and 218,000 patients with severe obesity who did not receive bariatric surgery were included in the study.

At 1 year post-surgery, surgical patients had a 48% lower risk of VTE than nonsurgical patients. Surgical patients’ risk of pulmonary embolism, a type of VTE that affects the lungs, was 70% lower. After 5 years, surgical patients had a 41% lower risk of VTE and a 55% lower risk of pulmonary embolism.

All types of surgery, including bariatric surgery, are known to increase the risk of blood clots in the short term. The researchers found that VTE risk 30 days after surgery was 5 times higher than for nonsurgical patients, which is in line with previous studies.

“We hypothesized at the beginning of this study that the risk of venous blood clots would change over time, and that is exactly what we saw,” Harrington said.

The researchers didn’t look at what caused risk to decrease, but they suggested that weight loss after surgery could be a factor. Obesity is well known to be associated with a greater risk of VTE.

VTE includes deep vein thrombosis and pulmonary embolism. Deep vein thrombosis happens when a blood clot forms in a vein deeper in the body, usually in the legs, thighs, pelvis, or arms. If a clot in a deep vein dislodges and travels to the lungs, it causes a pulmonary embolism, which partially or fully blocks blood flow to the lungs. Treatment can usually prevent the worst outcomes of VTE, but many people experience repeated episodes or longer-term complications.

“These results can help inform shared decision-making around bariatric surgery, which is a conversation between a patient and their doctor that looks at all the available information about different treatment options, their risks and benefits, and allows people to make the best choice for their individual situation,” said David Arterburn, MD, MPH, senior author on the paper and a senior investigator at KPWHRI.  

The study did not find any evidence that the risk of VTE was different based on age, body mass index, or sex.

Other research that Harrington is leading aims to evaluate risk factors such as physical activity and sedentary behavior in relation to VTE risk, while considering the complex role of obesity in these relationships.

The research was funded by the National Institute of Diabetes and Digestive and Kidney Diseases and the National Heart, Lung, and Blood Institute.

KPWHRI and Kaiser Permanente Washington coauthors are Eric Johnson, MS; Mary Kay Theis, MS; Julie Cooper, MPA; Christopher R. Daigle, MD; and Julietta H. Chang, MD.

By Amelia Apfel