The study from the University of Bristol is one of the first to find that for every five extra BMI units, a woman’s risk of womb (endometrial) cancer is almost doubled (increase of 88 per cent). This is higher than most previous studies have suggested and reflects lifelong weight status rather than a snapshot in time like most other studies. Five BMI units is the difference between the overweight category and the obese category, or of a 5’5 adult woman being two stones heavier. 

The international study looked at genetic samples from around 120,000 women from Australia, Belgium, Germany, Poland, Sweden, the UK, and the USA of which around 13,000 had womb cancer. This large statistical analysis is one of the first studies of its kind to look at the effect of lifelong greater BMI on womb cancer risk. 

The researchers looked at markers of 14 traits which could link obesity and womb cancer. They uncovered two hormones - fasting insulin and testosterone – which increased the risk of being diagnosed with womb cancer.  By pinpointing exactly how obesity increases the risk of cancer, such as through hormones, scientists in the future could use drugs to reduce or increase the level of these hormones in people already at a higher risk of cancer. For example, drugs like metformin used in diabetes treatment, can reduce the levels of hormones and research suggests this drug also affects cancer risk, though further study is ongoing. 

Read the full University of Bristol press release

Paper: ‘Identifying molecular mediators of the relationship between body mass index and endometrial cancer risk: a Mendelian randomization analysis’ by E Hazelwood et al. in BMC Medicine.