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The page below is a sample from the LabCE course Vitamin D Regulation, Clinical Significance and Treatment (by ASCLS). Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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1. A study of the association between serum 25-hydroxyvitamin D (25[OH]D) levels and all-cause mortality in 13,331 participants in the Third National Health and Nutrition Examination Survey (NHANES) showed (Melamed, M. L. et al. Arch Intern Med 2008;168:1629-1637) that....

A. Vitamin D insufficiency (25(OH)D = 10-25 ng/ml) was not associated with an increase in mortality (although there was a trend to an increase at the low end of insufficiency.
B. Vitamin D deficiency (25(OH)D < 10 ng/ml) had an approximately 1.5 fold increase risk of mortality with the confidence interval enough above 1.0 to be significant.
C. As in the cardiovascular disease studies, there was a suggestion that mortality could increase at very high levels of (25(OH)D.

2. In a study of older men,Cawthon P.M et al. (JCEM 2010 95: 4625-4634) found…

A. There was no association of 25(OH)D and mortality. B. There seemed to be an increased risk of mortality if serum PTH was elevated. This suggests that either the measurement of 25(OH)D is not a reliable predictor of vitamin D deficiency (and PTH is a more sensitive index of vitamin D deficiency) or that factors other than vitamin D like calcium absorption and/or excretion that could increase PTH are important.

Like fracture risk, true vitamin D deficiency is a cause for concern, whereas concern about vitamin D insufficiency is not as definitive.