Effects of 25-hydroxyvitamin D level and its change on parathyroid hormone in premenopausal Chinese women
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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.
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.
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 D3/day.
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).
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.
KeywordsCholecalciferol Fortification Milk Osteoporosis
This study was supported by Fonterra Brands Ltd, Auckland.
Conflicts of interest
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