Is low 25-hydroxyvitamin D linked to greater insulin resistance and higher cardiovascular event risk?

The relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and cardiometabolic health is a significant area of research, with evidence suggesting that low vitamin D status is a relevant marker for metabolic dysfunction and cardiovascular risk.

Clinical evidence for insulin resistance

Extensive observational and prospective evidence demonstrates a strong inverse association between serum 25(OH)D levels and markers of insulin resistance (IR), such as HOMA-IR and fasting insulin. Longitudinal studies confirm that baseline low 25(OH)D predicts future IR and an increased risk for metabolic syndrome (MetS), even after adjusting for potential confounders like BMI and age. Meta-analyses of supplementation trials indicate significant reductions in fasting insulin and improvements in insulin sensitivity, particularly in populations already presenting with MetS or pre-diabetes.

Cardiovascular event risk

Observational data consistently demonstrate a significant inverse association between serum 25(OH)D levels and the risk of major adverse cardiovascular events (MACE), including stroke and myocardial infarction. Low levels (typically <50 nmol/L) are linked to higher cardiovascular mortality, while higher baseline levels (>20 ng/mL) correlate with reduced MACE risk. Specifically, vitamin D deficiency is an independent determinant of coronary artery disease severity and is associated with increased coronary artery calcification. However, large-scale randomized controlled trials (such as VITAL and DO-HEALTH) have failed to show that universal vitamin D supplementation reduces MACE risk in the general population, suggesting that while low levels are a valid marker of risk, the relationship may not be straightforwardly causal.

Mechanistic explanations

The biological plausibility of these associations is supported by the role of Vitamin D Receptor (VDR) signaling:

• Pancreatic Protection: VDR activation in pancreatic beta-cells protects against oxidative stress, apoptosis, and inflammation, thereby preserving insulin secretory capacity.
• Insulin Action: Low levels of 25(OH)D reduce the availability of the active ligand (1,25(OH)2D), impairing pathways that normally enhance insulin receptor expression.
• Atherosclerosis and Inflammation: Deficiency is linked to increased pro-inflammatory markers (IL-6, TNF-α) and homocysteine, which promote atherosclerosis progression. VDR signaling normally exerts anti-inflammatory effects and may influence plaque stability; supplementation has been associated with a reduction in high-risk non-calcified plaque burden.

Bottom line

Low 25-hydroxyvitamin D is robustly associated with increased insulin resistance and higher cardiovascular event risk. While the evidence for metabolic dysfunction is particularly strong, the link to cardiovascular events is consistently observed in longitudinal studies, though universal supplementation has not yet been proven to prevent primary cardiovascular events in clinical trials.