A higher body mass index increases the risk of developing teen of the most common cancers, according to the largest study of its kind involving more than five million adults in the UK.

The study, published in The Lancet and carried out by researchers at the London School of Hygiene and Tropical Medicine (working with the Farr Institute of Health Informatics), estimate that over 12,000 cases of these 10 cancers each year are attributable to being overweight or obese. They calculate that if average BMI in the population continues to increase, there could be over 3,500 extra cancers every year as a result.

Using data from GP records in the UK’s Clinical Practice Research Datalink, the researchers identified 5.24 million individuals aged 16 and older who were cancer-free and had been followed for an average of 7.5 years. The risk of developing 22 of the most common cancers, which represent 90% of the cancers diagnosed in the UK, was measured according to BMI after adjusting for factors such as age, sex, smoking and socioeconomic status.

A total of 166,955 people developed one of the 22 cancers studied over the follow-up period and BMI was associated with 17 of them. Each 5 kg/m² rise in BMI was “clearly linked” with higher risk of cancers of the uterus (62% increase), gallbladder (31%), kidney (25%), cervix (10%), thyroid (9%) and leukaemia (9%).

Higher BMI also increased the overall risk of liver (19% increase), colon (10%), ovarian (9%) and breast cancers (5%), but the effects on these varied by other factors such as sex and menopausal status. Indeed, there was some evidence that those with high BMI were at a slightly reduced risk of prostate cancer and premenopausal breast cancer.

Lead author Krishnan Bhaskaran of LSHTM said that the number of people who are overweight or obese is rapidly increasing both in the UK and worldwide. He added that “it is well recognised that this is likely to cause more diabetes and cardiovascular disease. Our results show that if these trends continue, we can also expect to see substantially more cancers as a result.

The research was funded by the National Institute for Health Research, the Wellcome Trust and the Medical Research Council.