Sex-Specific BMI Trajectories in Young People With Type 1 Diabetes: A 20-Year Retrospective Regional Audit

The rates of obesity and type 1 diabetes (T1D) in children and adolescents are increasing in many settings worldwide, but data on weight gain in this group are limited in New Zealand. We examined temporal body mass index (BMI) changes and associated factors in young people with T1D in a mixed urban-rural region.

This study was a 20-year retrospective audit of clinical data from a regional paediatric diabetes service (June 2000-March 2021). The primary outcome was BMI standard deviation score (BMI SDS), whose trajectories from diagnosis were examined in association with demographic and clinical factors.

A total of 106 young people with T1D (56% male) were followed for a median of 8.3 years [Q1 = 6.1, Q3 = 11.0; maximum 15.1 years] and attended a median of 21 multidisciplinary clinic visits [Q1 = 12, Q3 = 30; range 1-56 visits]. In females, age at diagnosis modified the association between diabetes duration and BMI SDS (interaction p = 0.0009). Girls diagnosed at 4.0 years (age at diagnosis 25^th percentile for girls in our cohort) had no statistically significant change in BMI SDS over the first 5 years after diagnosis [-0.13 SDS (95% confidence interval [CI] -0.32 to 0.06); p = 0.18], while those diagnosed at 9.5 years (75^th percentile) experienced an increase of ≈0.39 SDS (0.08-0.70; p = 0.014). Among males, increasing age at diagnosis was associated with lower BMI SDS (p < 0.0001), whereas there was no statistically significant association with diabetes duration (p = 0.087). At any given duration, boys diagnosed at 11.1 years (age at diagnosis 75^th percentile for boys) had a BMI SDS approximately 0.70 lower (95% CI -1.02 to -0.45; p < 0.0001) than those diagnosed at 4.7 years (25^th percentile).

We observed sex-specific BMI trajectories in young people with T1D, with age at diagnosis exerting variable influences on BMI SDS trajectory in boys and girls. These findings support individualised T1D management strategies within multidisciplinary care.