June 15, 2007 (Los Angeles, CA) - Adults with low serum levels of vitamin D are more likely to have hypertension, diabetes, obesity, and high triglycerides than are adults with higher vitamin-D levels, an analysis of the third National Health and Nutrition Examination Survey (NHANES) shows [ 1]. Authors of the new analysis say their findings add to growing evidence suggesting it may be time to revisit public-health recommendations for vitamin-D intake.
"There's been more and more evidence that vitamin D is involved in a variety of bodily functions, including heart health," senior author on the study, Dr Keith Norris (Charles R Drew University of Medicine and Science, Los Angeles, CA), told heart wire . Current recommendations--ranging from 400 to 800 units in healthy adults to 1200 units in women with osteoporosis--are based on the relationship between vitamin D and parathyroid function for calcium regulation, he explained. "The recommended level of serum vitamin D is the level at which the parathyroid level does not become hyperactive, but we now know that vitamin D affects not only the parathyroid gland, but all these other systems in the body, and it appears we need even higher levels to have a positive effect on these other systems," he said.
The study appears in the June 14, 2007 issue of the Archives of Internal Medicine.
The vitamin du jour
Norris, with first author Dr David Martins (Charles R Drew University of Medicine and Science), used NHANES data collected between 1988 and 1994 to evaluate the link between serum vitamin-D levels and cardiovascular risk factors. They report that the adjusted prevalence of obesity, diabetes, high serum triglycerides, and high blood pressure were significantly higher among subjects in the lowest quartile of serum 25-hydroxyvitamin-D levels than in those in the highest quartile of vitamin-D levels. Women, the elderly, and ethnic minorities tended to have lower vitamin-D levels in the blood. Overall, more than half of almost all subgroups surveyed had insufficient 25-hydroxyvitamin-D levels, even by current standards (<30 ng/mL).
Odds ratio for CV risk factor in lowest vitamin-D quartile vs highest
|CV risk factor||Odds ratio||95% CI||p|
|High BP (>140/90 mm Hg)||1.30||1.13-1.49||.001|
|High triglycerides (>150 mg/dL)||1.47||1.30-1.65||<0.001|
|Diabetes (fasting blood glucose >126 mg/dL)||1.98||1.57-2.51||<0.001|
|Obesity (BMI>30 kg/m 2)||2.29||1.99-2.63||<0.001|
According to Norris, the findings with respect to blood pressure and diabetes are perhaps the most noteworthy, since these are such important contributors to cardiovascular disease. Moreover, animal studies have suggested that vitamin D may play a direct role in the development of hypertension and diabetes.
But Norris is also intrigued by the findings linking low vitamin-D with obesity. There are a number of plausible explanations indirectly linking low serum vitamin D to obesity: vitamin D may be stored in fat cells, rather than circulating in the blood, in people with more adipose tissue. It may also be a marker for the fact that obese subjects are often less active and spend less time outdoors, where UV light exposure increases vitamin-D levels. Norris, however, told heart wire that these "simple" explanations, in his mind, may not tell the whole story. Instead, his group is also investigating the effects of vitamin D on cell development.
"In the body, as a person grows and cells grow, there are different signals that tell these cells to become fat cells or muscle cells and that tell fat cells to express a lot of hormones that lead to becoming fatter or more insulin resistant or to becoming less fat or insulin resistant," he explained. "And I think vitamin D affects those pathways. We're now doing studies on adult stem cells looking at the effects of vitamin D on cell development, and we've at least found that the stem cells we're using respond to vitamin D. That allows us to start doing additional studies."
Another key step will be to show that supplementing vitamin D leads to improved cardiovascular outcomes, he noted. The implications, however, are far from trivial, particularly since vitamin-D supplementation is cheap, easy, and associated with minimal side effects.
"From a public-health perspective, if you can improve the health of 5% of 50 million people, that's a lot of people," Norris told heart wire .
Martins D, Wolf M, Pan D, et al. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States. Data from the third National Health and Nutrition Examination Survey. Arch Int Med 2007; 2007; 167:1159-1165.
The complete contents of Heart wire , a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.
Heartwire from Medscape © 2007 Medscape
Cite this: Shelley Wood. Low Vitamin D Linked to Increased CV Risk Factors - Medscape - Jun 15, 2007.