by
Joan Trombetti, Writer | August 12, 2008
On the basis of this finding, the researchers estimated that 20.6% of mortality risk could be attributable to vitamin D status with a population attributable risk percentage of 3.1% for those with the lowest vitamin D levels.
Although other studies have suggested that vitamin D deficiency could be a risk factor for cardiovascular- and cancer-related mortality, neither associations was significant in the NHANES analysis after adjustment for other factors.
Cardiovascular disease-related mortality was 70% higher among those with the lowest vitamin D levels than among those in the highest quartile in the unadjusted analysis. But this dropped to a nonsignificant elevation in risk similar in magnitude to that seen for all-cause mortality after adjustment for all factors (mortality rate ratio 1.20, 95% CI 0.87 to 1.64).
Cancer-specific mortality also appeared to increase with low vitamin D concentrations (mortality rate ratio 1.31, 95% CI 0.96 to 1.81), but the association fell away after adjustment for even a few factors including age, sex, race, and season of measurement (mortality rate ratio 1.05, 95% CI 0.74 to 1.47).
The strongest associations between vitamin D and mortality risk were found among participants without pre-existing cardiovascular disease (mortality rate ratio 1.54 versus 0.90, P=0.006 for interaction).
"If a causal relationship exists, 25-hydroxyvitamin D deficiency may play a role before cardiovascular disease is established," the investigators suggested.
The associations also tended to be stronger among those without hypertension (P=0.09 for interaction) or diabetes (P=0.09 for interaction) and among women (P=0.06 for interaction).
This argued "against low vitamin D levels being only a marker of poor general health," the researchers said, although these factors could still be involved in the mechanism of the effect.
They noted that the study could not infer causality because of its observational design and that residual confounding may have limited the findings.
The study, Dr. Melamed, and a co-author were supported by grants from the National Institutes of Health. Co-authors also reported support from Abbott Pharmaceuticals, the PJ Schafer Cardiovascular Research Fund, and the Paul Beeson Physician Faculty Scholars in Aging Program.
Source reference:
Melamed ML, et al "25-Hydroxyvitamin D Levels and the Risk of Mortality in the General Population" Arch Intern Med 2008; 168: 1629-1637.
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