Yet more evidence for D

On January 7, 2010, in Fat Solubles, Vitamins, by Andrea

At some point, people are going to figure out that vitamin D is important.  I don’t know when, but they will, and it will be tested for all people — not just those of us who scream loudly for it, and not just by those docs that pay attention to the studies.

Pay attention — vitamin D has been linked to cardiovascular disease, bone health, depression, stroke, diabetes, and many types of cancer.

Two reports in one day — one video and one report from Medscape — that show a corollary between heart disease in blacks and deficiency in vitamin D.

First, from Medscape:

Could Vitamin-D Deficiency Account for Higher CV Mortality in Blacks?

Sue Hughes

January 6, 2010 (Rochester, New York)Another paper suggesting a link between low levels of vitamin D and cardiovascular mortality has been published [1]. It also suggests that low vitamin-D levels may contribute to the increased cardiovascular mortality seen in the black population.

The study, published in the January-February 2010 issue of Annals of Family Medicine, was conducted by Drs Kevin Fiscella (University of Rochester School of Medicine, NY) and Peter Franks (University of California, Davis).

Fiscella commented to heartwire : “We know that people with darker skin have lower vitamin-D levels. And we know that African Americans have higher rates of cardiovascular disease than the white population. In our study, just two factors–poverty and low vitamin-D levels–seemed to explain the higher risk of cardiovascular mortality in the black population.”

In the paper, the authors note that low levels of vitamin D have been linked to cardiovascular disease and to cardiovascular risk factors such as obesity, hypertension, diabetes, peripheral arterial disease, and chronic renal disease.

They conducted a retrospective cohort study to examine the association of serum 25(OH)D levels with cardiovascular mortality and to look at the possible contribution of vitamin-D levels to black-white disparities in cardiovascular mortality. They used baseline data from the National Health and Nutrition Examination Survey collected between 1988 and 1994 (NHANES III) and data on cause-specific mortality through 2001 from the National Death Index. Complete data for all variables were available on 15 363 persons.

Results showed that participants with 25(OH)D levels in the lowest quartile (mean 13.9 ng/mL) compared with those in the three higher quartiles (mean 21.6, 28.4, and 41.6 ng/mL) had higher adjusted risk of cardiovascular death. There appeared to be a threshold effect, with little reduction in cardiovascular deaths above the 25th percentile. Those in the lowest quartile had an adjusted cardiovascular mortality risk 40% higher than the other three 25(OH)D quartiles (95% CI 16%–69%; p=0.001).

The relationship between race and cardiovascular mortality and the potential mediating effect of 25(OH)D was examined in a series of nested models. In the model adjusting only for outside variables (age, sex, month, and region), blacks showed significantly higher cardiovascular mortality than whites (incident rate ratio [IRR] 1.38). When 25(OH)D was added, there was a significant reduction of around 60% in the risk associated with black race (IRR 1.14), and when 25(OH)D and income were added together to the model, the increased risk in blacks was completely eliminated (IRR 1.01). The authors say this suggests that low 25(OH)D levels and poverty exert separate, additive effects on black cardiovascular mortality.

They add: “These findings are consistent with the notion that higher cardiovascular risk for blacks is partly related to lower levels of 25(OH)D,” but they add that supplements higher than those currently recommended would be needed to substantially increase levels among those in the lowest quartile.

They note that there are several sources of potential residual confounding in their analysis. For example, low 25(OH)D levels may represent a marker for poor health, or poor health may result in reduced sun exposure and consequent lower 25(OH)D levels. And unmeasured risk factors could also confound the results.

They point out that there are limited data from randomized controlled trials regarding the impact of vitamin-D supplementation on cardiovascular disease. But a meta-analysis of randomized trials of vitamin-D supplementation for other purposes, such as improvement in bone density and reduction in fractures, has shown a reduction in all-cause mortality, and other studies have suggested that vitamin-D supplementation may be associated with reductions in systolic blood pressure and reductions in proteinuria among patients with chronic kidney disease. It has also been suggested that statins represent analogs of vitamin D, they add.

Is It a Causal Relationship?

To heartwire , Fiscella commented: “If vitamin D is proven to be a causal risk factor (and this remains to be shown), then supplementing with vitamin D could help reduce cardiovascular disease and mortality in the whole population and to reduce the disparity we see between whites and blacks.

“We desperately need a randomized trial to look at vitamin-D supplementation in reducing cardiovascular disease. We have had a lot of false hopes before with vitamins, but there is a lot of basic science and epidemiology supporting a possible role for vitamin D in cardiovascular disease. There are many studies linking low vitamin-D levels to diabetes, hypertension, and peripheral vascular disease, and all of these are drivers of cardiovascular disease.”

He added: “We know low vitamin-D levels are implicated in poor health, but we don’t know which way that relationship works. Is it the lack of vitamin D that causes illness, or is it that people in poor health have suppressed appetites and don’t go outside enough and therefore don’t take in enough vitamin D?. And if vitamin-D deficiency is causal, will supplementation have a relatively quick benefit, or would you need to take it for years to see a benefit”?

Fiscella pointed out that the dose of vitamin D needed is also unknown. “The current recommendations are for a vitamin D intake of 400 units daily. But it may take much higher doses than this to have an effect on cardiovascular disease.”

And then from CNN.com:

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