Observational studies have suggested that vitamin D deficiency is associated with increased risk for AF, but few randomized trials have looked at the effect of vitamin D supplementation on AF incidence in healthy people.
The study, a post hoc analysis from a trial that explored the effects of vitamin D3 supplementation on incidence of cardiovascular diseases and cancer, included 2495 vitamin D-sufficient healthy older adults, mean age 68.2 years, of whom 43% were women.
Participants had been randomized to one of three groups in which they received vitamin D3 at either 1600 IU/day or 3200 IU/day, or placebo.
Atrial fibrillation was diagnosed in 190 participants.
Over a follow-up averaging 4.1 years, risk for incident AF was reduced by 27% for participants who received the 1600-IU/day dose compared with placebo; hazard ratio (HR), 0.73 (95% confidence interval [CI], 0.52 - 1.02; P = .07), and by 32% for those in the 3200-IU/day arm; HR, 0.68 (95% CI, 0.48 - 0.96; P = .03).
The incident-AF risk was reduced by 30% in a comparison of the two vitamin D groups combined versus the placebo group; HR, 0.70 (95% CI, 0.53 - 0.94; P = .02).
After exclusion of 122 participants who reported being on antiarrhythmic medications at baseline, the 1600-IU/day group showed a significant 27% reduction in risk for AF (95% CI, 4% - 58%; P = .03) and the 3200-IU/day group a nonsignificant 30% (95% CI, 5% - 53%; P = .08) reduction in risk.
High-dose vitamin D3 supplementation may reduce incidence of AF in a generally healthy, largely vitamin D-sufficient elderly population, the authors propose. Additional controlled trials are needed, especially in diverse populations, they note.
The study was conducted by Jyrki K. Virtanen, PhD, University of Eastern Finland, Institute of Public Health and Clinical Nutrition, Kuopio, and colleagues.
Atrial fibrillation was not prespecified as a primary outcome, and the results differ from those of other randomized controlled trials. Information on type of AF (whether paroxysmal or nonparoxysmal, for example) wasn't available nor were participants' history of AF. All participants were White and from Finland, limiting generalizability of the results.