Low levels of vitamin D are associated with reductions in blood vessel functioning, but this may not translate into an effect on cardiovascular disease incidence, according to the results from two new studies.
The seemingly conflicting studies report that vitamin D status may have effects on blood pressure, and the functioning of blood vessels, but also that vitamin D levels have no effect on the risk of cardiovascular disease.
The first study, presented at the annual American College of Cardiology meeting in New Orleans, adds to the evidence that a lack of vitamin D may lead to reduced vascular health, contribute to high blood pressure, and increase the risk of cardiovascular disease (CVD).
The research data presented by Dr Ibhar Al Mheid, a cardiovascular researcher at Emory University School of Medicine, reported that that even after controlling for factors a number of potential confounding factors, such as age, weight and cholesterol, otherwise healthy volunteers with low vitamin D levels still had stiffer arteries and impaired blood vessel functions, when compared to those with adequate vitamin D status.
However, the second study, a prospective cohort study investigating the effects of vitamin D on the heart health of over 3000 men, reports that 25(OH) vitamin D and vitamin D intake are not significantly associated with CVD outcomes.
The study, led by K. Messenger from the Center for Research on Occupational & Environmental Toxicology, at the Oregon Health & Science University, prospectively evaluated the association of dietary plus supplemental vitamin D intake and serum 25(OH) vitamin D with CVD incidence, finding no association.
Vit D for CVD?
Cardiovascular disease (CVD) is the most common cause of death worldwide.
Many studies have associated low 25(OH) vitamin D status with various CVD risk factors; including elevated blood pressure (hypertension), high levels of blood lipids (hyperlipidemia), and metabolic syndrome.
However, research has yet to conclusively backup such associations, and the question of whether vitamin D is a risk factor for CVD remains unclear.
Previous research has also highlighted the high concern of skin cancer (from UV exposure) as a reason why fewer people are not achieving sufficient vitamin D levels.
Therefore, understanding the role of vitamin D status in the risk and possible prevention of cardiovascular disease is important for public health.
The American College of Cardiology researchers studied 554 generally healthy participants with and average age of 47 and, finding that the 14 percent of volunteers had 25-hydroxyvitamin D levels considered deficient (less than 20 nanograms per millilitre) whilst 33 percent had levels considered insufficient (under 30 nanograms per millilitre).
“We found that people with vitamin D deficiency had vascular dysfunction comparable to those with diabetes or hypertension,” said Dr Al Mheid, lead author of the research.
Volunteers with vitamin D levels that increased over the next six months, either from dietary supplements or ample sun exposure, tended to improve their measures of vascular health and had lower blood pressure, said Al Mheid.
The researchers observed that participants with vitamin D insufficiency, whose levels later rose to normal levels, also experienced a drop in blood pressure, by an average of 4.6 millimeters mercury.
“There is already a lot known about how vitamin D could be acting here … It could be strengthening endothelial cells and the muscles surrounding the blood vessels. It could also be reducing the level of angiotensin, a hormone that drives increased blood pressure, or regulating inflammation,” said Al Mheid.
Using data from the Osteoporotic Fractures in Men (MrOS) Study, the Oregon Health & Science University researchers studied the association of 25(OH) vitamin D with both CVD and cardiovascular mortality, in what they report to be “the first longitudinal cohort study to analyze the association of vitamin D intake with CVD.”
The researchers measured vitamin D intake using a food frequency questionnaire and self-reported supplemental intake in 3094 men (mean age 76.4 years). From a subset of this population, they then measured 25(OH) vitamin D levels in 813 men.
“There was no significant association between 25(OH) vitamin D or vitamin D intake and CVD outcomes. Standard risk factors for CVD, such as age, history of CVD and medication use, were strong predictors of CVD and included as covariates, but 25(OH) vitamin D and vitamin D intake were not independently associated with CVD incidence,” wrote Messenger and colleagues.
“Given the limited data from clinical trials and the prevalence of vitamin D deficiency, additional investigations are necessary to evaluate the efficacy of vitamin D supplementation on CVD risk,” they concluded.
Source: American College of Cardiology meeting
Presentation on Sunday 3 April 2011 by Dr Ibhar Al Mheid
Source: Nutrition, Metabolism & Cardiovascular Diseases
Published online ahead of print, doi: 10.1016/j.numecd.2010.10.019
“Serum and dietary vitamin D and cardiovascular disease risk in elderly men: A prospective cohort study”
Authors: W. Messenger, C.M. Nielson, H. Li, T. Beer, E. Barrett-Connor, K. Stone, J. Shannon