Young adulthood adiposity in relation to all-cause and cause-specific mortality: a prospective study of 0.5 million Chinese adults

Obesity is a well-established risk factor for early death, but the exact shapes of associations between young adulthood body mass index (BMI) and mortality in later life were not well characterised. Using data from the prospective China Kadoorie Biobank study of 430,373 participants (∼57% being women, with a median follow-up duration of 12 years), Cox regression analysis was performed to yield adjusted hazard ratios (HRs) relating BMI at ∼25 years old (BMI 25 ) with different mortality outcomes including total mortality ( n = 36,814), cardiovascular mortality ( n = 13,620), cancer mortality ( n = 13,394) and respiratory mortality ( n = 2929). Mean BMI 25 of participants was 21.9 (SD = 2.5) kg/m 2 , and 1.9% participants were obese at young adulthood (i.e., BMI 25 ≥28.0 kg/m 2 ). Independent of baseline BMI, higher BMI 25 was associated with much higher levels of blood glucose and diabetes prevalence at baseline. After adjusting for potential confounders e.g., age, smoking, and baseline measured BMI, BMI 25 had a strong positive log-linear association with all above-mentioned mortality outcomes, those being obese at young adulthood had a HR of 1.85 (95% CI: 1.75–1.95), 1.85 (1.71–2.00), 1.40 (1.26–1.56) and 2.34 (1.96–2.81), respectively, compared with participants having BMI 25 of 18.5–20.0 kg/m 2 . The association with cancer mortality was more pronounced in men than in women, but no such heterogeneity was observed for total, CVD, and respiratory mortality. To conclude, the observed strong monotonically positive associations between young adulthood BMI and various mortality outcomes, independent of BMI in later life, support the need for early and stringent body weight control to prevent early death.