Adequate levels of vitamin D may control or prevent coronary artery disease, high blood pressure, and heart failure. A heart attack may result when these conditions aren’t treated. Researchers are trying to determine whether vitamin D can prevent heart attacks and, if so, how much vitamin D is needed. They are also curious to learn what vitamin D can do after a person has a heart attack.
Vitamin D levels and heart attack risk
If high vitamin D status can prevent the conditions that are risk factors for a heart attack (also called a myocardial infarction), it seems logical that it will also lower the risk of heart attacks. There are some large association studies to support this idea. These studies show that people with low vitamin D status (lower than 15 ng/ml or 37.5 nmol/L) are at the highest risk of suffering a heart attack, and that people with serum 25-hydroxyvitamin D over 30 ng/ml (75 nmol/L) are most protected.
This relationship holds true even after the researchers adjust for all the factors that can cause heart attacks, such as the following:
Family history of heart attacks
Body mass index
Alcohol consumption
Physical activity
Diabetes
High blood pressure
That’s still not absolute proof, but it suggests that the relationship between vitamin D and heart attacks may not be because vitamin D status is a marker for some other well known cause of the disease.
The problem with these studies is that while the statisticians attempt to adjust for factors such as family history, body weight, etc., they can only guess the true effect that these factors are having in the outcome.
Ultimately, someone has to do a clinical trial in which people are randomly assigned to a vitamin D or a placebo treatment group, and the incidence of heart attacks is then examined over the next several years. Without such evidence, it isn't known for certain that an association between vitamin D and heart attacks indicates direct cause and effect.
Researchers don’t yet know the dietary or serum level of vitamin D that is required to prevent heart attacks and heart failure. However, it’s clear that having very low vitamin D status (serum 25-hydroxyvitamin D less than 15 ng/ml [37.5 nmol/L]) is the worst place to be. Make sure you keep your vitamin D intake up so that you don’t fall below this level.
The role of vitamin D after a heart attack
Studies that look at the role of vitamin D after a heart attack are rare. This may be because other drugs are used after a heart attack, so it’s hard to determine whether the vitamin D or something else is having an impact on future cardiovascular events.
One study that tried to address the question was published in the American Heart Journal in June 2010. The authors looked at vitamin D levels in people who’d had an acute cardiovascular event, such as a heart attack or heart failure, but were stable at the beginning of the study. They measured vitamin D levels and followed the patients for up to eight years.
The authors didn’t find a difference in future cardiovascular events between those who had high levels of vitamin D (greater than 30 ng/ml or 75 nmol/L) and those who had low levels of vitamin D (less than 15 ng/ml or 37.5 nmol/L serum 25-hydroxyvitamin D). This suggests there may be a limit to what vitamin D can do for the heart.