A longitudinal study tracking people as they develop type 1 diabetes shows that C-peptide levels maintain a steady decline starting six months before clinical diagnosis.

The results suggest that interventions aimed at reducing damage to beta-cells might need to be carried out earlier than previously thought, the US authors say.

Data for 80 people enrolled in the TrialNet Pathway to Prevention study were used. All had relatives with type 1 diabetes and were positive for auto-antibodies associated with the disease but did not have diabetes when they were enrolled.

All had later developed the disease, with clinical diagnosis defined as fasting glucose greater than 7mmol/L, or two-hour glucose greater than 11.1 mmol/L, on two successive glucose tolerance tests within two months.