Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) characterised by long-lasting inflammation and ulcers (sores) in the lining of the colon.

Ulcerative colitis incidence

UC commonly affects teenagers and young adults, but the disease can also occur in children and older individuals. Until recently, evidence regarding the effect of low body mass index (BMI) in young adults on the risk of developing ulcerative colitis in later years was inconclusive. However, according to an April 2019 study by Mendall and colleagues published in Scientific Report, low BMI in young men was associated with an increased risk of UC in a 40-year follow-up study.

This Danish cohort study followed a total of 377,957 young men born during 1939–1959, with weight measured at age 19, from 1977 to the end of 2015 and monitored their health records. This was a follow-up study, and after 13 million person-years of follow up, a total of 3,323 subjects developed UC. The study’s results suggest that for each 1kg/m2 increase in BMI, the hazard of UC decreased by 2%. The study also found an association between low BMI and Crohn’s disease.

UC incidence has steadily increased over the years in developed countries. GlobalData epidemiologists forecast an increase in diagnosed incident cases of UC in men in the seven major markets (7MM: US, France, Germany, Italy, Spain, the UK, and Japan), which will grow by an annual growth rate (AGR) of 1.6%, from 52,000 cases in 2016 to 60,000 cases in 2026. Understanding the role of associated conditions such as BMI is important to analyse the trend of UC incidence.

Although this study found no strong association, smoking is suspected to increase the risk of both low BMI and UC. Another possible explanation is reverse causality, where low BMI is an indication of early stage or subclinical UC. As this cohort study provided evidence of the association between low BMI earlier in life and the later development of UC, future research could explore the possible mechanisms in this relationship.