A recent study published in the British Medical Journal found that taking a vitamin D supplement may reduce the incidence of heart attacks and other major cardiovascular events.
D-Health Trial FindingsThe D-Health trial, a large randomized, double-blind clinical study, found that older adults who took monthly doses of vitamin D for five years reduced the incidence of major cardiovascular events, particularly myocardial infarction (heart attack) and coronary revascularization, treatments that restore limited or blocked blood flow to the heart.
The study included over 21,000 Australian participants aged 60 to 84. At the beginning of each month for five years, half received one capsule of 60,000 international units (IU) of vitamin D3; the other half received a placebo.
Researchers used hospital admission data and deaths to identify major cardiovascular events, including heart attacks, strokes, and coronary revascularization.
They reported a 19 percent lower rate of heart attack and an 11 percent drop in risk for coronary revascularization in the vitamin D group. There was no difference in the rate of stroke between groups.
The rate of major cardiovascular events was 9 percent lower in the vitamin D group compared with placebo, an equivalent of 5.8 fewer events per 1,000 participants.
While some study participants using statins or other cardiovascular (CV) drugs before and during the trial showed that vitamin D may have induced a more substantial effect, researchers reported these results as statistically insignificant.
“Vitamin D at low dosages has low toxicity,” Ms. Neale said, “so I think it would be reasonable for clinicians to consider supplementing elderly people who don’t have contraindications, particularly those with underlying risk factors for CV disease.”
Although prior studies have reported no significant benefit of vitamin D supplementation in reducing the risk of cardiovascular disease (CVD), study design limitations have been challenged.
The VITAL StudyOne of the largest previous studies, the VITAL study, funded by the National Institutes of Health (NIH) and run by Brigham and Women’s Hospital, included nearly 26,000 U.S. men and women aged 50 to 55 and older who were monitored for an average of 5.3 years for the occurrence of cardiovascular events and cancer.
The study investigated whether taking daily dietary supplements of vitamin D3 (2,000 IU) and omega-3 fatty acids (1 gram) would reduce the risk for heart disease, cancer, and stroke in those with no prior history.
While VITAL researchers concluded that high-dose vitamin D does not lower the risk of developing CVD or cancer in generally healthy men and women, the study found it does appear to reduce the risk of cancer death.
Study FlawsInfante, et al. (pdf) found numerous flaws with the study and published their review, "VITAL Study: An Incomplete Picture?" in the European Review for Medical and Pharmacological Sciences.
All participants, including those in the placebo group, were permitted to take up to 800 IU of vitamin D daily, which was about 40 percent of the tested intervention (2,000 IU per day), resulting in the study design failing to meet the criteria of a randomized placebo-controlled trial fully.
There was also a lack of blood level assessment, except in a small subgroup of only 6.4 percent of all participants assessed at one year.
In addition, the trial failed to include information about sun exposure, outdoor physical activity, indoor activity, or body-covering habits, which would have highlighted potential differences in the groups.
The Importance of Vitamin DVitamin D is essential to heart health, improving blood flow by keeping the inner lining of blood vessels healthy, reducing inflammation, and helping to lower high blood pressure.
As both a nutrient and hormone, it affects many bodily functions, including strengthening bones and supporting the immune system.
We can raise our vitamin D levels through diet and supplementation, and our bodies produce vitamin D when our bare skin is exposed to sunlight.
Vitamin D-Rich FoodsFew foods contain vitamin D naturally, and most are from animal sources. Foods with some of the highest levels of vitamin D include:
- Fatty fish, such as salmon, trout, cod, sardines, and mackerel.
- Egg yolks, especially from free-range or pasture-raised chickens. Eggs from chickens exposed to regular sunlight have three to four times the vitamin D level as chickens raised indoors.
- Mushrooms, the only nonanimal source with a sufficient amount of vitamin D, other than fortified foods.
- Dairy products, such as yogurt, cheese, and kefir.
Vitamin D SupplementationThe NIH recommends a 600-IU vitamin D3 supplement daily and warns that toxicity with higher doses originates from the recommendation from the 2010 Institute of Medicine (IOM) Dietary Reference, which was based on adequate amounts of D3 for skeletal health only.
Frequency of DoseAlthough D-Health trial participants were given a monthly dose, which may have led to a higher adherence rate, there's growing evidence that daily dosing may be more beneficial to health outcomes in certain diseases.
Testing Vitamin D Blood LevelsBaseline testing and monitoring of vitamin D blood levels are essential for determining if amounts obtained from combined sun exposure, food, and supplementation are adequate to prevent deficiency and achieve health goals.
According to the Office of Dietary Supplements, vitamin D blood level status is measured by the 25-hydroxy level in nanomoles/liter (nmol/L).
Researchers have yet to determine the exact parameters of low and high vitamin D levels. Still, Food and Nutrition Board (FNB) experts at the National Academies of Sciences have concluded that people are at risk of vitamin D deficiency at serum 25-hydroxyvitamin D level concentrations less than 30 nmol/L, at risk of inadequacy at 30 to 50 nmol/L. Levels of 50 nmol/L or more are sufficient for most people.
In contrast, the Endocrine Society stated that, for clinical practice, a serum 25-hydroxyvitamin D concentration of more than 75 nmol/L is necessary to maximize the effect of vitamin D on calcium, bone, and muscle metabolism. The FNB committee also noted that serum concentrations greater than 125 nmol/L may be associated with adverse reactions.
While there are varying opinions about vitamin D supplementation, its effect on cardiovascular health, adequate levels, and how much is too much is ultimately a decision you and your doctor should make together.