Design: Population-based registry linkage cohort
Population: 5,202 people with type 1 diabetes diagnosed before age 16 in New South Wales
Primary outcome: 20-year incidence of chronic complications by age at onset
Effect: Onset <7 vs 13-16 y: retinopathy aHR 0.25 (0.17-0.36); kidney 0.40 (0.30-0.53)

An Australian registry linked 5,202 people diagnosed with type 1 diabetes before age 16 between 1990 and 2009 to hospital, emergency, insurance and death records to 2019. Kidney complications were the commonest within 20 years of onset, at 53.4 per 10,000 person-years, and cardiac complications the least common, at 9.2.

Compared with onset at 13 to under 16, onset before age 7 was associated with lower 20-year risk of nearly every complication: severe retinopathy (adjusted HR 0.25, 95% CI 0.17 to 0.36), peripheral neuropathy (0.16, 0.08 to 0.32), kidney complications (0.40, 0.30 to 0.53) and cardiac complications (0.32, 0.15 to 0.66). Lower-limb infections were the exception. When risk was compared by attained age rather than duration, it did not differ.

The pattern fits the idea that prepubertal years of diabetes contribute less to complication risk. The practical implication is the reverse: children diagnosed in adolescence accumulate risk faster and deserve the closest screening.

Treat adolescent-onset type 1 diabetes as the higher-risk group for early complications.
Do not relax retinopathy or kidney screening in young adults because they were diagnosed young; risk by attained age was similar.
Kidney complications were the commonest within 20 years — keep albuminuria testing on schedule through transition to adult care.
Use transition clinics to confirm screening has not lapsed between paediatric and adult services.

Why it matters

It explains why two young adults with the same diabetes duration can carry very different complication risk.

The statistics, in plain English

A hazard ratio of 0.25 means about a quarter of the rate of severe retinopathy, after adjustment. These are associations from linked records, which pick up only complications that reached hospital or insurance data, so milder disease is missed.