Associations of social determinants of health with life expectancy and future health risks among individuals with type 2 diabetes: two nationwide cohort studies in the UK and USA.

BACKGROUND

Social determinants of health (SDHs) are the primary drivers of preventable health inequities, and the associations between SDHs and health outcomes among individuals with type 2 diabetes remain unclear. This study aimed to estimate the associations of combined SDHs with life expectancy and future health risks among adults with type 2 diabetes from the UK and USA.

METHODS

In an analysis of two nationwide cohort studies, adults with type 2 diabetes were identified from the UK Biobank from March 13, 2006, to Oct 1, 2010 (adults aged 37-73 years) and the US National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018 (adults aged ≥20 years). Participants with type 2 diabetes at baseline were included in our analysis. Participants without information on SDHs or follow-up were excluded. The UK Biobank assessed 17 SDHs and the US NHANES assessed ten SDHs, with each SDH dichotomised into advantaged and disadvantaged levels. The combined score of SDHs were calculated as the sum of the weighted scores for each SDH. Participants were then categorised into tertiles (favourable, medium, and unfavourable SDH groups). Primary outcomes were life expectancy and mortality in both cohorts, and incidences of cardiovascular disease, diabetes-related microvascular disease, dementia, and cancer in the UK Biobank. Outcomes were obtained from disease registries up until Dec 31, 2021, in the UK Biobank and Dec 31, 2019, in the US NHANES cohorts.

FINDINGS

We included 17 321 participants from the UK Biobank cohort (median age 61·0 years [IQR 56·0-65·0]; 6028 [34·8%] women and 11 293 [65·2%] men) and 7885 participants from the NHANES cohort (mean age 59·2 years [95% CI 58·7-59·6]; 3835 [49·1%, weighted] women and 4050 [50·9%, weighted] men) in our analysis. In the UK Biobank, 3235 deaths (median follow-up 12·3 years [IQR 11·5-13·2]), 3010 incident cardiovascular disease (12·1 years [10·8-13·0]), 1997 diabetes-related microvascular disease (8·0 years [7·1-8·9]), 773 dementia (12·6 years [11·8-13·5]), and 2259 cancer cases (11·3 years [10·4-12·2]) were documented; and the US NHANES documented 2278 deaths during a median follow-up of 7·0 years (3·7-11·2). After multivariable adjustment, compared with the favourable SDH group, the hazard ratio was 1·33 (95% CI 1·21-1·46) in the medium SDH group and 1·89 (1·72-2·07) in the unfavourable SDH group in the UK Biobank cohort; 1·51 (1·34-1·70) in the medium SDH group and 2·02 (1·75-2·33) in the unfavourable SDH group in the US NHANES cohort for all-cause mortality; 1·13 (1·04-1·24) in the medium SDH group and 1·40 (1·27-1·53) in the unfavourable SDH group for incident cardiovascular disease; 1·13 (1·01-1·27) in the medium SDH group and 1·41 (1·26-1·59) in the unfavourable SDH group for incident diabetes-related microvascular disease; 1·35 (1·11-1·64) in the medium SDH group and 1·76 (1·46-2·13) in the unfavourable SDH group for incident dementia; and 1·02 (0·92-1·13) in the medium SDH group and 1·17 (1·05-1·30) in the unfavourable SDH group for incident cancer in the UK Biobank cohort (p<0·010 for each category). At the age of 45 years, the mean life expectancy of participants was 1·6 years (0·6-2·3) shorter in the medium SDH group and 4·4 years (3·3-5·4) shorter in the unfavourable SDH group than in the favourable SDH group in the UK Biobank. In the US NHAHES cohort, the life expectancy was 1·7 years (0·6-2·7) shorter in the medium SDH group and 3·0 years (1·8-4·3) shorter in the unfavourable SDH group, compared with the favourable group.

INTERPRETATION

Combined unfavourable SDHs were associated with a greater loss of life expectancy and higher risks of developing future adverse health outcomes among adults with type 2 diabetes. These associations were similar across two nationwide cohorts from varied social contexts, and were largely consistent across populations with different demographic, lifestyle, and clinical features. Thus, assessing the combined SDHs of individuals with type 2 diabetes might be a promising approach to incorporate into diabetes care to identify socially vulnerable groups and reduce disease burden.

FUNDING

The National Natural Science Foundation of China, the National Key R&D Program of China, and the Fundamental Research Funds for the Central Universities.