Context:
Optimal levels of vitamin D have
been a topic of heavy debate, and the correlation between 25-hydroxyvitamin D
[25(OH)D] levels and mortality still remains to be established.
Objective:
The aim of the study was to
determine the association between all-cause mortality and serum levels of
25(OH)D, calcium, and PTH.
Design and Setting:
We conducted a retrospective,
observational cohort study, the CopD Study, in a single laboratory center in Copenhagen,
Denmark.
Participants:
Serum 25(OH)D was analyzed from
247,574 subjects from the Copenhagen general practice sector. In addition,
serum levels of calcium, albumin-adjusted calcium, PTH, and creatinine were
measured in 111,536; 20,512; 34,996; and 189,496 of the subjects, respectively.
Main Outcome Measures:
Multivariate Cox regression analysis
was used to compute hazard ratios for all-cause mortality.
Results:
During follow-up (median, 3.07 yr),
15,198 (6.1%) subjects died. A reverse J-shaped association between serum level
of 25(OH)D and mortality was observed. A serum 25(OH)D level of 50–60
nmol/liter was associated with the lowest mortality risk. Compared to 50
nmol/liter, the hazard ratios (95% confidence intervals) of all-cause mortality
at very low (10 nmol/liter) and high (140 nmol/liter) serum levels of 25(OH)D
were 2.13 (2.02–2.24) and 1.42 (1.31–1.53), respectively. Similarly, both high
and low levels of albumin-adjusted serum calcium and serum PTH were associated
with an increased mortality, and secondary hyperparathyroidism was associated
with higher mortality (P < 0.0001).
Conclusion:
In this study from the general
practice sector, a reverse J-shaped relation between the serum level of 25(OH)D
and all-cause mortality was observed, indicating not only a lower limit but
also an upper limit. The lowest mortality risk was at 50–60 nmol/liter. The
study did not allow inference of causality, and further studies are needed to
elucidate a possible causal relationship between 25(OH)D levels, especially
higher levels, and mortality.
Note: 50-60 nmol/L equals 20-24
ng/ml. To convert nmol/L to ng/ml, divide by 2.5. To convert ng/ml to nmol/L,
multiply by 2.5.
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