Green leafy and cruciferous vegetable consumption and risk of type 2 diabetes: results from the Singapore Chinese Health Study and meta-analysis

Abstract

Several previous prospective studies suggest that consumption of green leafy and cruciferous vegetables may lower the risk of type 2 diabetes (T2D). We investigated the association between consumption of different types of vegetables in relation to T2D risk in an Asian Population. We included 45 411 participants (age range: 45-74 years) of the Singapore Chinese Health Study (SCHS) free of diabetes, cancer or CVD at baseline (1993-1998). Dietary information was collected using a validated FFQ. Physician-diagnosed incident diabetes was reported at follow-up I (1999-2004) and II (2006-2010) interviews. Cox proportional hazards regression was used to estimate hazard ratio (HR) and 95 % CI of T2D risk. An updated meta-analysis was also conducted to summarise results for green leafy and cruciferous vegetables. During 494 741 person-years of follow-up, 5207 incident T2D occurred. After adjustment for potential confounders, neither total vegetables (top v. bottom quintile HR=1·08; 95 % CI 0·98, 1·18, P trend=0·66) nor specific vegetables including dark green leafy vegetables (HR=1·05; 95 % CI 0·96, 1·15, P trend=0·21) and cruciferous vegetables (HR=0·97; 95 % CI 0·88, 1·06, P trend=0·29) were substantially associated with risk of T2D. A meta-analysis (eleven studies with 754 729 participants and 58 297 cases) including the SCHS and all previous prospective studies suggested borderline significant inverse associations between green leafy (summary relative risk (RR)=0·91; 95 % CI 0·84, 1·00) and cruciferous vegetable consumption (RR=0·87; 95 % CI 0·76, 1·00) and T2D risk, with moderate-to-high heterogeneity. In conclusion, green leafy or cruciferous vegetable consumption was not substantially associated with risk of T2D in an Asian population. Meta-analysis of available cohort data indicated that evidence for a beneficial effect of green leafy or cruciferous vegetable consumption on T2D risk is not convincing.

Keywords: HR hazard ratio; RR relative risk; SCHS Singapore Chinese Health Study; SWHS Shanghai Women’s Health Study; T2D type 2 diabetes; Cohort studies; Diets; Meta-analyses; Type 2 diabetes; Vegetables.