Consumption of whole grains and refined grains and associated risk of cardiovascular disease events and all-cause mortality: a systematic review and dose-response meta-analysis of prospective cohort studies

Background: Although relationships between the intake of whole grains and refined grains and the incidence of cardiovascular disease (CVD) events and all-cause mortality have been investigated, the conclusions have been inconclusive. Objectives: We aimed to comprehensively summarize the evidence about the correlation between consuming whole grains and refined grains and risks of CVD events and all-cause mortality and to evaluate the meta-evidence quality. Methods: We searched PubMed, Embase, and Web of Science until 15 March, 2022. Random-effects models were employed to calculate summary relative risks (RRs) and 95% confidence intervals (CIs). We explored potential linear or nonlinear relationships using restricted cubic splines. The NutriGrade tool was employed to rate meta-evidence quality. Results: Twenty-four articles (68 studies; 46 for whole grains and 22 for refined grains) with 1,624,407 participants were included. Per 30-g increase in daily whole grain consumption, the RRs and 95% CIs of stroke, coronary heart disease (CHD), heart failure (HF), CVD, and all-cause mortality were 0.98 (0.96, 1.00), 0.94 (0.92, 0.97), 0.97 (0.89, 1.07), 0.92 (0.88, 0.96), and 0.94 (0.92, 0.97), respectively. Whole grain consumption was linearly associated with CHD (P-nonlinearity = 0.231) and nonlinearly associated with CVD (P-nonlinearity = 0.002) and all-cause mortality (P-nonlinearity = 0.001). Except for a positive correlation between refined grain consumption and all-cause mortality in the restricted cubic spline, no significant influence of refined grain intake on stroke, CHD, HF, and CVD was detected. The meta-evidence quality for the association of whole grain consumption with stroke, CHD, HF, CVD, and all-cause mortality was moderate, moderate, low, high, and high, respectively. For refined grains, all meta-evidence was of low quality. Conclusions: Consuming whole grains, rather than refined grains, can assist in preventing CHD, CVD, and all-cause mortality. Relationships between consumption of refined grains and health outcomes should be interpreted cautiously because of the low quality of meta-evidence.