Vitamin D and Atrial Fibrillation
Atrial fibrillation (AF) is the most common sustained arrhythmia, affecting ~3% of adults. Vitamin D deficiency is associated with higher AF prevalence in cross-sectional data, but the story is complicated — some supplementation trials hint at increased AF risk with very high doses.
Observational deficiency signal
Cross-sectional studies find lower mean 25(OH)D in AF patients than controls; U-shaped relationships have been reported — both very low and very high 25(OH)D may associate with elevated AF risk. Rahimi 2011 reported adults with 25(OH)D > 100 nmol/L had higher AF prevalence than sufficient adults.
The VITAL AF substudy
In the VITAL trial (25,000 adults; 2,000 IU vitamin D + 1 g EPA/DHA or placebo × 5 years), the vitamin D arm did not increase incident AF overall. However, the omega-3 arm had a small but significant increase in AF (particularly at higher doses in follow-up studies), consistent with earlier signals from REDUCE-IT and STRENGTH trials.
High-dose vitamin D concerns
Rare case reports link acute hypercalcaemia from vitamin D overdose with new-onset AF. Vitamin D at physiological repletion doses (up to 4,000-5,000 IU/day) has not been associated with increased AF risk in general trial evidence. Extreme mega-dosing (10,000+ IU/day chronically) has less certain safety profile.
What actually manages AF
- Anticoagulation for stroke prevention if CHA₂DS₂-VASc ≥ 2 in men or ≥ 3 in women (DOACs preferred over warfarin in non-valvular AF).
- Rate control (beta-blocker, calcium channel blocker, digoxin) or rhythm control (antiarrhythmics, ablation).
- Address underlying drivers: hypertension, obesity, sleep apnoea, alcohol excess.
- Vitamin D correction in the deficient is reasonable adjunctive care; do not use as substitute for anticoagulation.