Vitamin D status, genetic factors, and risks of cardiovascular disease among individuals with type 2 diabetes: a prospective study

The presence of a threshold effect has been proposed, suggesting that beneficial effects from vitamin D supplementation may only be present when the vitamin D concentration is below a particular threshold. We investigated the associations of serum 25-hydroxyvitamin D [25(OH)D] concentrations and genetic factors with risks of total and subtypes of cardiovascular disease (CVD) in individuals with type 2 diabetes (T2D), among whom vitamin D deficiency or insufficiency is particularly common. This prospective study included 15,103 individuals with T2D who were initially free of CVD and had serum 25(OH)D measurements in the UK Biobank. Incidences of total and subtypes of CVD, including ischemic heart disease (IHD) and stroke, were ascertained via electronic health records. Weighted genetic risk scores (GRSs) were constructed for IHD and stroke. The mean serum 25(OH)D concentration was 43.4 nmol/L (SD: 20.4 nmol/L), and 65.7% of participants had a vitamin D concentration below 50 nmol/L. During a median of 11.2 years of follow-up, 3534 incident CVD events were documented. Compared with individuals with 25(OH)D concentrations <25 nmol/L, participants with 25(OH)D concentrations ≥75 nmol/L had HRs (95% CIs) of 0.75 (0.64, 0.88) for CVD, 0.69 (0.56, 0.84) for IHD, and 0.74 (0.52, 1.06) for stroke. Participants with 25(OH)D concentrations ≥50 nmol/L and low GRSs, as compared with individuals with 25(OH)D concentrations <25 nmol/L and high GRSs, had a 50% (39%, 65%) lower risk of IHD. No significant interactions were demonstrated between serum 25(OH)D concentrations and the GRSs and genetic variants in vitamin D receptors (VDR). Higher serum 25(OH)D concentrations were significantly associated with lower risks of total CVD and IHD among patients with T2D, regardless of their genetic susceptibility and the genetic variants in VDR. Risk reductions tended to plateau at serum 25(OH)D levels around 50 nmol/L. These findings suggest that maintaining an adequate vitamin D status and avoiding deficiency may help to prevent CVD complications among patients with T2D.