Social deprivation modifies the association between incident foot ulceration and mortality in type 1 and type 2 diabetes: a longitudinal study of a primary-care cohort

AIMS/HYPOTHESIS: The aim of this study was to determine whether social deprivation in the presence of diabetes is an independent predictor of developing a foot ulcer and separately of mortality. METHODS: This was a primary-care-based retrospective analysis of 13,955 adults with type 1 (n = 1370) or type 2 (n = 12,585) diabetes after a median follow-up of 10.5 years. Demographic characteristics, indices of social deprivation and clinical variables were assessed at baseline. The primary outcomes were new foot ulceration (in those without a previous history of foot ulcers) and all-cause mortality. Cox proportional hazard models were used to describe the associations among foot ulceration, social deprivation and mortality. RESULTS: The mean age of the population was 69.4 (range: 16–89) years. The incidence of foot ulceration was greater in individuals with type 2 (8.6%) compared with type 1 diabetes (4.8%). Occurrence was similar by sex, but increased with age and deprivation index. Individuals in the highest quintile of deprivation were 77% more likely to develop a foot ulcer compared with those in the lowest quintile (OR 1.77 [95% CI 1.45, 2.14], p < 0.0001). Overall, 2946 (21.1%) deaths were recorded. Compared with individuals without a foot ulcer, the development of a foot ulcer was associated with a higher age- and sex-adjusted mortality rate (25.9% vs 14.0%), and a 72% (HR 1.72 [95% CI 1.56, 1.90], p < 0.001) increased risk of mortality in those with type 2 diabetes. Risk of death increased by 14% per quintile of deprivation in a univariable analysis (HR 1.14 [95% CI 1.10, 1.17]). In multivariable Cox regression analyses, there was a 48% increased risk of mortality in individuals with a foot ulcer (HR 1.48 [95% CI 1.33, 1.66]) independent of the Townsend index score (HR 1.13 [95% CI 1.10, 1.17], per quintile), baseline age, sex, diabetes type, smoking status, hypertension, statin use, β-blocker use, metformin use, HbA(1c) levels and insulin use. CONCLUSIONS/INTERPRETATION: This study confirms the high mortality rate in individuals with diabetes-related foot ulcers. In addition, socioeconomic disadvantage was found to be an independent effect modifier, contributing to an increased burden of mortality in people with diabetes who develop foot ulceration. In light of this, and as diabetes service configurations are orientated for the next 5–10 years, modelling of foot ulceration risk needs to take socioeconomic disadvantage into account. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00125-017-4522-x) contains peer-reviewed but unedited supplementary material, which is available to authorised users.