Atrial fibrillation (often abbreviated as AF or AFib) is a common type of arrhythmia, or irregular heartbeat, where the heart beats too rapidly, irregularly, or both. It specifically affects the heart’s atria, which are the two upper chambers of the heart. This is one of the most common types of arrhythmias and can lead to big problems and complications. In a new study, researchers found that vitamin D could help protect against this AFib, but there’s a catch: it only works at a very high doe.

For a common vitamin, Vitamin D is pretty unusual and controversial. For starters, you get much of the vitamin not from the food you eat, but rather from the Sun. During exposure to sunlight, a substance in your skin is converted to something called “previtamin D3” which, in turn, becomes the vitamin itself. The effects of the vitamin are also pretty striking.

Vitamin D has been linked to everything from melanoma to COVID-19 to autoimmune diseases, but the dose is also controversial. Studies sometimes use very high doses of vitamin D, way over the recommended dose. This could suggest that the recommended dose should be increased, but it could also indicate that the benefits of high doses of the vitamin are not worth it (since high doses of vitamin D can cause issues).

This is exactly the case in this study.

The study was conducted at the University of Eastern Finland over a period of 6 years, from 2012 to 2018. The trial, called the Finnish Vitamin D Trial, or FIND, wanted to explore how vitamin D supplementation affect various cardiovascular diseases and cancers. Overall, the study looked at almost 2500 participants. The participants, either 60-year-old or older men or 65-year-old or older women were split into three groups:

• the first group got a supplement of 40 micrograms per day (2x the recommended dosage);
• the second group got 80 micrograms per day (4x the recommended dosage);
• the third group got a placebo.

All groups were also allowed to take their personal vitamin D supplement, which is up to 20 micrograms per day.

Over the course of the five-ear study, 190 participants were diagnosed with atrial fibrillation. Out of these, 76 are in the placebo group, 59 in the first group, and 40 in the second group. In other words, the risk of attrial fibrilation was about a third lower in all the high-dose groups.

The new study suggests that higher doses could offer some protection, but the high dose is pretty concerning.

“In conclusion, our findings suggest possible benefit in AFib prevention with high-dose vitamin D supplementation in an elderly population, despite the relatively high baseline concentrations,” the researchers write in the study.

Journal Reference: Virtanen, J. K., et al. (2023) The effect of vitamin D3 supplementation on atrial fibrillation in generally healthy men and women –the Finnish Vitamin D Trial. American Heart Journal. doi.org/10.1016/j.ahj.2023.05.024.