Association Between Type 2 Diabetes Onset Age and Risk of Cardiovascular Disease and Mortality: Two Cohort Studies from United Kingdom and Hong Kong

•There is limited evidence to evaluate the CVD and mortality risk between people with and without diabetes in particular for young age group, this study aims to evaluate the effects of young T2DM onset on CVD and mortality risk.•Our study highlights the importance of prevention of T2DM and pre-T2DM in young adults, and the urge for stringent control of the T2DM and co-existing CVD risk factors for young T2DM patients. This study evaluated the association between age of onset of type 2 diabetes mellitus (T2DM) and risk of cardiovascular disease (CVD) and mortality. Two retrospective cohort studies were conducted using the electronic health record from United Kingdom (UK) and Hong Kong (HK) (2008-2013) on adults without CVD. 128,918 and 185,646 patients with newly diagnosed T2DM were assigned to the T2DM group, and control group included 5,052,770 and 3,159,396 patients without T2DM in UK and HK cohort, respectively. The groups were divided into six groups based on age at baseline adjusted with fine stratification weights and multivariable Cox regression adjusted for baseline characteristics and weighting. After 11.6 and 9.5 median follow-up years in UK and HK cohort, T2DM was associated with increased CVD and mortality risk, but the risks decreased with age. In the UK cohort, the risk of CVD with T2DM onset at the age 18-39 (hazard ratio (HR) (95% confidence interval (CI)): 3.22 (2.80, 3.71)) was higher than the group at age 60-69 (1.21 (1.15, 1.26)) and age ≥ 80 (0.99 (0.93, 1.05)). Similarly, the risk of mortality among young onset of T2DM with age at 18-39 (2.41 (2.06, 2.83)) were higher than those with age 60-69 (1.40 (1.34, 1.46)) and age ≥80 (1.12 (1.08, 1.16)). Results from the HK cohort show a similar pattern. Young onset of T2DM is associated with a great impact on cardiovascular health later in life. This highlights the importance of prevention of DM in young adults. (247 words)