Vitamin D insufficiency defined by serum 25-hydroxyvitamin D and parathyroid hormone before and after oral vitamin D₃ load in Japanese subjects.
Vitamin D insufficiency is a risk for both skeletal and nonskeletal health. However, some ambiguity remains about threshold serum 25(OH)D for vitamin D insufficiency. To determine the threshold serum 25(OH)D to maintain normal calcium availability without elevation in serum parathyroid hormone (PTH) among Japanese subjects with various calcium intakes, we conducted a multicenter prospective open-labeled study. We recruited 107 ambulatory subjects without disorders affecting vitamin D metabolism to whom oral vitamin D₃ 800 IU/day for 4 weeks or 1,200 IU/day for 8 weeks was given. Serum 25(OH)D, PTH, calcium, phosphate, and magnesium were measured before and after vitamin D₃ supplementation. Calcium intake was assessed by questionnaires. When all the data were combined, serum 25(OH)D was negatively correlated with PTH. The cubic spline curve between serum 25(OH)D and PTH indicated PTH reached its plateau between 35 and 40 pg/ml at 25(OH)D between 25 and 30 ng/ml. Vitamin D₃ supplementation increased serum 25(OH)D and decreased PTH. Change in PTH correlated positively with baseline serum 25(OH)D. From the regression analyses, baseline serum 25(OH)D above 28 ng/ml corresponded to the threshold level without reduction in PTH after vitamin D₃ supplementation. In multivariate regression analyses, age but not calcium intake was a significant determinant of PTH. We concluded that a serum 25(OH)D level of 28 ng/ml was identified as a threshold for vitamin D insufficiency necessary to stabilize PTH to optimal levels.
Okazaki
Ryo
R
Third Department of Medicine, Teikyo University Chiba Medical Center, 3426-3 Anesaki, Ichihara, Chiba, Japan. rokazaki@med.teikyo-u.ac.jp
Sugimoto
Toshitsugu
T
Kaji
Hiroshi
H
Fujii
Yoshio
Y
Shiraki
Masataka
M
Inoue
Daisuke
D
Endo
Itsuro
I
Okano
Toshio
T
Hirota
Takako
T
Kurahashi
Issei
I
Matsumoto
Toshio
T
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002762:Cholecalciferol / Q000008:administration & dosage* / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000097:blood / Q000188:drug therapy; D010281:Parathyroid Hormone / Q000097:blood*; D011446:Prospective Studies; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood*
D010281:Parathyroid Hormone; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D