AIMS: This retrospective, longitudinal study characterised 2430 adults (mean age 40.8±16.1years) with newly diagnosed type 1 diabetes (T1D) over the first 5years of insulin treatment.

METHODS: Data from 1year pre- and up to 5 years post-insulin initiation were extracted from the UK Clinical Practice Research Datalink (1990-2013). Baseline HbA1c, BMI and Charlson comorbidity index (CCI) score were compared with data at 1, 2, 3 and 5 years.

RESULTS: Mean HbA1c decreased significantly from baseline 95±32.8mmol/mol (10.8±3.0%) to 61±21.9mmol/mol (7.7±2.0%) at 1year, remaining significantly lower at 2, 3 and 5 years (p<0.0001). One year after initiating insulin, only 6.3% of patients had HbA1c <48mmol/mol (<6.5%). There was no further improvement in HbA1c after 1year. Mean BMI increased significantly from baseline 25.3±5.5kg/m2 to 27.2±5.8kg/m2 at 1year; p<0.0001), remaining significantly higher thereafter, with over two-thirds having overweight/obesity by year 5. Mean CCI score increased significantly (1.32, baseline; 1.46, year 1; 1.75, year 5). CCI patterns were similar within BMI and HbA1c strata.

CONCLUSIONS: More intensive support to reach and maintain glycaemic targets soon post-diagnosis, while avoiding weight gain, and prevention and optimal management of comorbidities are warranted.