Long-term time in target range for body mass index (BMI) and diabetes incidence: insights from CHARLS

Body mass index (BMI) is strongly associated with the development of type 2 diabetes. However, the association between long-term time in target range (TTR) for BMI and the incidence of new-onset diabetes remains unclear.

This study utilized a non-diabetic population aged 45 years or older from the China Health and Retirement Longitudinal Study (CHARLS). BMI-TTR was assessed in Waves 1, 2, and 3 over a 5-year period, with the target range defined as 18.5 kg/m² ≤ BMI < 23 kg/m². New-onset diabetes in Waves 2, 3, and 4 over a 6-year follow-up served as the study endpoint. After applying exclusion criteria, 6662 participants (3143 men and 3519 women; mean age 58.93 ± 8.85 years) were enrolled. Participants were categorized into four groups (TTR1-TTR4) based on the number of times BMI was within the target range (0-3 times). The risk of new-onset diabetes decreased progressively with increasing BMI-TTR during follow-up. Compared with the TTR1 group, participants in the TTR4 group exhibited a significantly lower risk of diabetes (adjusted HR: 0.577, 95% CI: 0.463-0.720, P < 0.001), even after adjusting for baseline BMI (adjusted HR: 0.685, 95% CI: 0.537-0.872, P = 0.002). This effect was even more pronounced in female subgroup and in individuals aged under 60 years of age.

In adults aged 45 years or older, regardless of baseline BMI, maintaining BMI within the target range over time was associated with a reduced risk of new-onset diabetes, particularly among women and individuals under 60 years of age. These findings highlight the importance of long-term weight management in diabetes prevention.