People who have undergone gastric bypass are five times more likely to develop anaemia than those with obesity treated non-surgically, according to a study with up to 20 years’ follow-up.

Vertical-banded gastroplasty and gastric banding were also linked to anaemia but to a lesser extent, the data showed.

“These findings highlight the importance of long-term compliance to nutritional supplementation and monitoring to enable prevention and early detection of serious nutritional deficiencies after bariatric surgery,” wrote the researchers, from the Karolinska Institutet, Sweden.

While other studies had looked at nutritional deficiencies after bariatric surgery, the current study was the first with a control group to follow patients for more than a decade, the authors said.