Effects of 25-hydroxyvitamin D level and its change on parathyroid hormone in premenopausal Chinese women.
Optimal levels of 25-hydroxyvitamin D [25(OH)D] were investigated in premenopausal Chinese women. Parathyroid hormone (PTH) change at 3 months was associated with change in 25(OH)D but not with baseline levels, and PTH fell even when starting levels of 25(OH)D were >40 nmol/L, consistent with optimal values for 25(OH)D of ≥40 nmol/l.


BACKGROUND
The upper level of 25-hydroxyvitamin D [25(OH)D] which constitutes a long-term bone health risk by causing elevated PTH levels is uncertain. Although many studies have addressed this question using cross-sectional data, the present study is one of few employing a prospective approach to determine 25(OH)D levels required to minimize PTH.


METHODS
Relationships among baseline values and 3-month changes (Δ) in PTH and 25(OH)D were assessed in 221 Chinese women, aged 28.0±4.4 years (mean±SD), taking part in a placebo-controlled dairy product intervention delivering 200 IU vitamin D(3)/day.


RESULTS
Baseline 25(OH)D was 34±11 nmol/L and was inversely related to baseline PTH (r=-0.18, P=0.007), with a plateau in PTH levels when 25(OH)D was >40 nmol/L. After 3 months intervention, PTH fell 11% and neither Δ25(OH)D nor ΔPTH differed between treatment and control groups. ΔPTH was inversely related to Δ25(OH)D (P<0.001) but not to baseline 25(OH)D. Similarly, ΔPTH differed between quartiles of Δ25(OH)D (P<0.001), but not between quartiles of baseline 25(OH)D and no interaction was observed between quartiles of baseline 25(OH)D and Δ25(OH)D. Even in the highest quartile of baseline 25(OH)D (>40 nmol/L), PTH fell 0.4±0.1 pmol/L (mean±SEM; P=0.008).


CONCLUSIONS
We conclude that vitamin D deficiency is common in young women in Hong Kong. The cross-sectional analysis indicates that optimal 25(OH)D is >40 nmol/L, and the longitudinal data is consistent with a higher optimal value which is not defined in this study's results.
Bacon
C J
CJ
Department of Medicine, University of Auckland, Auckland, New Zealand. c.bacon@auckland.ac.nz
Woo
J
J
Lau
E M C
EM
Lam
C W K
CW
Gamble
G D
GD
Reid
I R
IR
D000328:Adult; D002762:Cholecalciferol / Q000008:administration & dosage; D003611:Dairy Products; D005260:Female; D005500:Follow-Up Studies; D005527:Food, Fortified; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood*; D017697:Premenopause / Q000097:blood; D011446:Prospective Studies; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000502:physiology; D014808:Vitamin D Deficiency / Q000097:blood* / Q000178:diet therapy; D055815:Young Adult
C470125:PTH protein, human; D010281:Parathyroid Hormone; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D