Up to 7% of study participants were vitamin D deficient
The 25(OH)D analysis indicated that 3.9% of UK Biobank and 3.7% of Copenhagen study participants were deficient, compared with 6.9% in EPIC-CVD.
Across the full range of 25(OH)D concentrations, there was no significant association between genetically predicted 25(OH)D levels and CHD, stroke, or all-cause mortality.
However, restricting the analysis to individuals deemed vitamin D deficient (25[OH]D concentration < 25 nmol/L) revealed there was “strong evidence” for an inverse association with all-cause mortality, at an odds ratio per 10 nmol/L increase in genetically predicted 25(OH)D concentration of 0.69 (P < .0001), the team notes.
There were also nonsignificant associations between being in the deficient stratum and CHD, at an odds ratio of 0.89 (P = .14), and stroke, at an odds ratio of 0.85 (P = .09).
Further analysis suggests the association between 25(OH)D concentrations and all-cause mortality has a “clear threshold shape,” the researchers say, with evidence of an inverse association at concentrations below 40 nmol/L and null associations above that threshold.
They acknowledge, however, that their study has several potential limitations, including the assumption in their Mendelian randomization that the “only causal pathway from the genetic variants to the outcome is via 25(OH)D concentrations.”
Moreover, the genetic variants may affect 25(OH)D concentrations in a different way from “dietary supplementation or other clinical interventions.”
They also concede that their study was limited to middle-aged participants of European ancestries, which means the findings “might not be applicable to other populations.”
The study was funded by the British Heart Foundation, Medical Research Council, National Institute for Health Research, Health Data Research UK, Cancer Research UK, and International Agency for Research on Cancer. Dr. Burgess has reported no relevant financial relationships. Disclosures for the other authors are listed with the article.
A version of this article first appeared on Medscape.com.