Low blood vitamin D concentrations may increase mortality risk

A new review suggests that mortality risk decreases as the vitamin D serum level increases, with optimal concentrations of 75–87.5 nmol/L.

To evaluate a potential association of 25-hydroxyvitamin D [25(OH)D] serum concentrations and mortality among general populations, 14 prospective cohort studies were reviewed in which 5,562 deaths occurred among 62,548 individuals (1). A meta-analysis of the studies showed that an increase in vitamin D serum concentrations of 12.5, 25, and 50 nmol/L from a median reference level of 27.5 nmol/L resulted in a reduction in mortality risk of up to 31%. However, there was no significant decrease in mortality associated with levels increased to 87.5 nmol/L above the reference level.

The researchers commented that while the Institute of Medicine already considers concentrations of 50 nmol 25(OH)D/L to be adequate (2), other scientists maintain that the most advantageous serum concentrations begin at 75 nmol 25(OH)D/L and that the optimal are between 90 and 100 nmol 25(OH)D/L (3). The new data on overall mortality would be further evidence for a desirable concentration of 75–87.5 nmol 25(OH)D/L.

A meta-analysis of randomized, controlled trials that were designed mainly to evaluate musculoskeletal conditions of frail, elderly people showed a significant reduction of total mortality in the vitamin D treatment groups (4). In the majority of studies included in that meta-analysis, baseline circulating concentrations were 50 nmol 25(OH)D/L. Even in apparently healthy subjects, circulating concentrations 50 nmol 25(OH)D/L are common around the world (5). There is some evidence for a nonlinear association of 25(OH)D with conditions, such as breast cancer (6), incidence of cardiovascular diseases (7), and all-cause mortality (8).

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8. Melamed M. L. et al. 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med. 2008; 168:1629–1637.