This study aimed to assess the association between body mass index (BMI) and the development of severe hypoglycaemia in patients with type 2 diabetes (T2D), using nationwide data for the entire South Korean population.

The association between BMI and severe hypoglycaemia was retrospectively examined from claims and National Health examination data registered between 2002 and 2015. A total of 1,366,692 subjects assigned clinical codes for T2D and prescribed antihypoglycaemic agents were included. The primary outcome was an episode of severe hypoglycaemia after the baseline health examination.

A total of 37,682 subjects (2.7%) experienced a new severe hypoglycaemic event during the follow-up period (mean: 8.6 years). An inverse J-shaped association was observed between BMI and severe hypoglycaemic events. The association between low BMI and high risk of severe hypoglycaemia was similar in subjects who had never smoked, did not consume alcohol, did not use insulin and had no major comorbidities, after adjusting for multiple confounding variables. This association was also found to be intensified in men, young people aged 30–49 years, those with major comorbidities and insulin users.

BMI and severe hypoglycaemia were found to be inversely associated. Thus, those who fall into the category of having low BMI and high risk of severe hypoglycaemia should be warned about the risk of having a hypoglycaemic event and be properly informed about hypoglycaemia to minimize the risk of fatal hypoglycaemia-related outcomes.