New research published in the International Journal of Cardiology has found that supplementation with vitamin D improves cardiac autonomic tone in healthy subjects.
Cardiac autonomic tone is a medical term that refers to the heart’s ability to respond to a stressor and return to normal functioning. A stressor is a chemical agent, stimulus or event that causes a physiological stress response in the body. An example of a stressor includes losing your job, running a marathon or public speaking.
Several studies have found a correlation between vitamin D deficiency and increased risk of cardiovascular events, with many finding an association between low vitamin D levels and sudden arrhythmic death. Impaired cardiac autonomic tone is a central characteristic of sudden arrhythmic death and changes in autonomic tone in the heart is part of a cascade of events that leads to cardiac arrest, or the stopping of one’s heart.
Since low vitamin D levels have been associated with sudden arrhythmic death, researchers wanted to know if this might be by way of influencing cardiac autonomic tone. They decided to find out.
Researchers enrolled thirteen healthy subjects (10 premenopausal females, 3 males) into their study. To evaluate cardiac autonomic tone, researchers measured the frequency of the subjects’ heartbeats in response to a stressor. Low frequencies meant a diminished autonomic tone (bad), while higher frequencies signaled a healthy autonomic response (good). Accordingly, a high ratio of low frequencies to high frequencies is bad, while a relatively low ratio is good.
In this study, the stressor was a hormone called Angiotensin II (AngII). AngII, for example, will increase in response to stress and can cause changes in the heart’s ability to function normally.
After an initial test to establish a baseline autonomic response to both a low and a high dose of AngII, eleven of the subjects ingested 5,000 IU vitamin D3 (cholecalciferol) and two supplemented with 10,000 IU for 28 days. The researchers did not specify why they gave more vitamin D to two of the subjects, but most likely the reason was that these subjects had significantly lower serum vitamin D levels and needed the extra supplementation to bring them up to acceptable levels.
Before supplementation, the subjects showed a poor response to AngII administration as expected, with a ratio of low frequency to high frequency heart rates of 2.4.
After 28 days of vitamin D supplementation, the patients were administered AngII once again. This time, the patients saw an improvement in response to a low level of the cardiac stressor. The ratio of low frequency to high frequency heart rates improved to 1.4 in response to AngII administration.
However, there were no differences in the subjects’ responses to the high dose of AngII, meaning that the responses at baseline and after supplementation were about the same.
These results suggest that vitamin D supplementation improves cardiac autonomic tone in response to a small amount of a cardiac stressor in healthy humans, but perhaps not in response to a large stressor.
This was novel and interesting pilot research that should help us understand how vitamin D might help in cardiovascular health and perhaps even in sudden arrhythmic death. However, it’s important to note that the study was small, and there was no placebo group to compare to.
The researchers noted “larger, prospective studies are required to determine the effect of vitamin D3 supplementation on clinical outcomes,” but that “optimizing vitamin D levels remains an exciting potential therapeutic target for those populations at high risk of cardiovascular mortality.”