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

• Published in: The American journal of clinical nutrition 2009-06, Vol.89 (6S), p.1997S-2008S
• Main Authors: Seamans, Kelly M, Cashman, Kevin D
• Format: Article
• Language: English
• Subjects: age; Biological and medical sciences; Biomarkers; Biomarkers - blood; Bone Density; bone metabolism; Calcium; Calcium - pharmacokinetics; Clinical trials; dietary mineral supplements; dietary minerals; Dietary Supplements; endpoints; Feeding. Feeding behavior; Fundamental and applied biological sciences. Psychology; Humans; Intestinal Absorption; literature reviews; meta-analysis; Methods; nutrient uptake; Nutrition; Nutrition Assessment; Nutritional Status; parathyroid hormone; Parathyroid Hormone - blood; regression analysis; temporal variation; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Vitamin D; Vitamin D - analogs & derivatives; Vitamin D - blood; vitamin supplements; Vitamins - blood
• ISSN: 0002-9165; 1938-3207
• DOI: 10.3945/ajcn.2009.27230D

BACKGROUND: 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. OBJECTIVE: 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. DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.