Benefits of Retained Insulin for Good Health

The purpose of this research is to understand the impact of retained endogenous insulin (as measured by C-peptide) on quality of life and related outcomes in people living with insulin treated diabetes, and, in those living with type 1 diabetes, to determine the pragmatic and non-pragmatic C-peptide measures which have the strongest association with clinical benefit (including repeated home samples and derived measures of beta cell function). The investigators will do this in two ways: Firstly, the investigators will extend a large existing prospective study of new adult onset diabetes (Getting the Right Classification and Treatment From Diagnosis in Adults With Diabetes (StartRight)) https://clinicaltrials.gov/ct2/show/NCT03737799) which has followed 1800 participants for median 4 years from diabetes diagnosis. Participants with insulin treated diabetes will be invited to take part in a further research visit remotely or face to face. The investigators will assess the longitudinal relationship between C-peptide and the available quality of life, mental health status and healthcare utilisation measures over up to 9 years from diabetes diagnosis and assess additional measures in cross sectional analysis. In the second part of this research, the investigators will utilise cohorts of over 2500 participants with type 1 diabetes, measured C-peptide and consent to recontact to recruit 200 participants with a range of C-peptide. Eligible participants with C-peptide measured in clinical care may also be invited to take part. The investigators will undertake detailed assessment of complex and pragmatic measures of C-peptide and beta cell function and compare performance in predicting glycaemic outcomes (using data from continuous glucose monitors) and (where relevant) patient reported outcomes.

ARM 1 Inclusion Criteria: * Previously recruited to the StartRight study (NCT03737799) with consent to be contacted for further research * Clinical diagnosis of diabetes \& Insulin treated * Able and willing to provide informed consent/assent. * Aged 18 years or older. ARM 2 Inclusion Criteria: * Clinical diagnosis of Type 1 diabetes * Known C-peptide, measured as part of previous research or as part of diabetes clinical care OR Where C-peptide is not measured, participant must be within 7 years of diagnosis and have at least 1 positive islet antibody, measured at any time since diabetes diagnosis. * Where measured C-peptide is \>600pmol/L, previous positive islet autoantibodies. * Able and willing to provide informed consent * Aged 18 years or older Exclusion Criteria: \- Renal failure defined by eGFR \