Article

Existing and potentially novel functional markers of vitamin D status: a systematic review.

Department of Food and Nutritional Sciences, University College Cork, Cork, Ireland.
American Journal of Clinical Nutrition (impact factor: 6.67). 05/2009; 89(6):1997S-2008S. DOI:10.3945/ajcn.2009.27230D pp.1997S-2008S
Source: PubMed

ABSTRACT Although serum 25-hydroxyvitamin D [25(OH)D] is the currently accepted vitamin D status marker of choice, use of other biomarkers or functional endpoints have been suggested.
The objective was to systematically review the effectiveness of 25(OH)D, parathyroid hormone (PTH), bone turnover markers, bone mineral density (BMD), and calcium absorption as biomarkers of vitamin D status.
Methods included a structured search on Ovid MEDLINE, EMBASE (Ovid), and Cochrane CENTRAL; rigorous inclusion/exclusion criteria; data extraction; quality assessment; meta-analysis; and meta-regression.
Thirty-six vitamin D supplementation randomized controlled trials (RCTs) and 4 before-after studies were included. Vitamin D supplementation significantly raised circulating 25(OH)D in all but one RCT, but the response was highly heterogeneous [weighted mean difference (WMD): 34.1 nmol/L; 95% CI: 28.9, 39.2; 32 RCTs; I2 = 97%). Vitamin D supplementation (without calcium) significantly lowered circulating PTH (WMD: -0.29 pmol/L; 95% CI: -0.56, -0.02; 11 RCTs; I2 = 29%), but this was not apparent in the presence of calcium supplementation. There was a suggestion that whole-body or lumbar spine BMD may be a useful biomarker in older people but not in adolescents. Bone turnover markers were not useful biomarkers of vitamin D status, but 4 before-after studies suggested that intestinal calcium absorption may respond to vitamin D status.
This systematic review confirmed that circulating 25(OH)D is a robust and reliable marker of vitamin D status. Further research is needed to clarify which population subgroups show responses of PTH, BMD, and/or calcium absorption in response to changes in vitamin D status.

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Keywords

4 before-after studies
 
accepted vitamin D status marker
 
bone mineral density
 
bone turnover markers
 
calcium supplementation
 
circulating 25(OH)D
 
Cochrane CENTRAL
 
data extraction
 
functional endpoints
 
intestinal calcium absorption
 
Ovid MEDLINE
 
parathyroid hormone
 
RCTs
 
rigorous inclusion/exclusion criteria
 
serum 25-hydroxyvitamin D [25(OH)D]
 
systematically review
 
useful biomarker
 
vitamin D status
 
Vitamin D supplementation
 
vitamin D supplementation randomized
 

Kelly M Seamans