Individuals with lower blood levels of vitamin D appear to have an increased risk of death overall and from cardiovascular causes, according to a report in the June 23 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.
A recent consensus panel estimated that about 50 percent to 60 percent of older individuals in North America and the rest of the world do not have satisfactory vitamin D status, and the situation is similar for younger individuals, according to background information in the article. Blood levels of 25-hydroxyvitamin D, a measure of blood vitamin D levels, lower than 20 to 30 nanograms per milliliter have been associated with falls, fractures, cancer, immune dysfunction, cardiovascular disease and hypertension. These effects are thought to be mediated by the compound 1,25-dihydroxyvitamin D, which is produced by the body and also converted from 25-hydroxyvitamin D.
Harald Dobnig, M.D., of Medical University of Graz, Austria, and colleagues studied 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels in 3,258 consecutive patients (average age 62 years) who were scheduled for coronary angiography testing at a single medical center between 1997 and 2000.
During about 7.7 years of follow-up, 737 (22.6 percent) of participants died, including 463 (62.8 percent) who died of cardiovascular causes. Death rates from any cause and from cardiovascular causes were higher among individuals in the lower one-half of 25-hydroxyvitamin D levels and the lowest one-fourth of 1,25-dihydroxyvitamin D levels. These associations remained when the researchers accounted for other factors, including coronary artery disease, physical activity level and co-occurring diseases.
Low 25-hydroxyvitamin D levels also were correlated with markers of inflammation such as C-reactive protein, as well as signs of oxidative (oxygen-related) damage to cells, the authors note.
"Apart from the proved effects that vitamin D has on bone metabolism and neuromuscular function, appropriate serum levels (that may also be higher than in the present investigation) are associated with a decrease in mortality," they conclude. "Although not proved, it seems possible that at least part of this effect may be due to lowering of a risk profile promoting atherosclerosis [narrowing of the arteries] and preventing cardiovascular end points."
"Based on the findings of this study, a serum 25-hydroxyvitamin D level of 20 nanograms per milliliter or higher may be advised for maintaining general health."
While cross-sectional studies have linked vitamin D to cardiovascular disease, these findings are the first to show elevated mortality, they noted.
Notably, even vitamin D insufficiency increased mortality risk 33% to 54%, so Dr. Dobnig's group recommended a serum 25-hydroxyvitamin D level of 20 ng/mL or higher for maintaining general health.
Dobnig et al say that these results show that a low 25-hydroxyvitamin-D level can be considered a strong risk indicator for all-cause mortality in women and in men.
They note that while the percentage of patients with low 25-hydroxyvitamin-D values in this study may seem unexpectedly high, with roughly two-thirds of those included having levels below 20 ng/mL, they point out that the mean value of 17.3 ng/mL compares well with values reported from other large trials performed in middle European countries such as France, Italy, and Germany.
This study by itself does not prove the direction of causality. For example, people who get more exercise outside will get more vitamin D from the sun shining on them. But they will also get more exercise. Also, people who eat fish will get more vitamin D in their diet. But they'll also get heart healthy omega 3 fatty acids. But this study fits with a larger pattern in studies of vitamin D and health and so I think it likely that vitamin D is providing some benefit. But if you get the vitamin D by exercising outside and eating salmon you won't have to worry which factor is delivering the benefit.
|Share |||Randall Parker, 2008 June 24 09:20 PM Aging Diet Heart Studies|