Optimal vitamin D status and serum parathyroid hormone concentrations in African American women.
BACKGROUND
Optimal vitamin D status for the prevention of osteoporosis has been inferred from examinations of the serum 25-hydroxyvitamin D [25(OH)D] concentration below which there is an increase in serum parathyroid hormone (PTH).


OBJECTIVE
The objectives of the study were to ascertain whether a threshold for serum 25(OH)D exists below which serum PTH increases and whether persons with 25(OH)D above this threshold have lower rates of bone loss than do persons with 25(OH)D below the threshold.


METHODS
The relation of serum 25(OH)D to serum PTH was analyzed in 208 African American women studied longitudinally for 3 y. These healthy women in midlife were randomly assigned to receive placebo or 800 IU vitamin D3/d; after 2 y, the vitamin D3 supplementation was increased to 2000 IU/d. Both groups received calcium supplements to ensure an adequate calcium intake. A systematic literature review found a wide range of threshold values in part due to varied calcium intake.


RESULTS
A Loess plot suggested a breakpoint between 40 and 50 nmol/L for serum 25(OH)D. A line-line model was fitted to the data, and it showed a spline knot at 44 nmol/L. A heuristic approach verified that PTH does not decline as rapidly when the serum concentration of 25(OH)D is >40 nmol/L as when it is <40 nmol/L. We found no significant difference in rates of bone loss between persons with 25(OH)D concentrations above and below 40 nmol/L.


CONCLUSIONS
Although a threshold for 25(OH)D can be identified, we suggest that it should not be used to recommend optimal vitamin D status.
Aloia
John F
JF
Bone Mineral Research Center, Winthrop University Hospital, Mineola, NY 11501, USA. jaloia@winthrop.org
Talwar
Sonia A
SA
Pollack
Simcha
S
Feuerman
Martin
M
Yeh
James K
JK
D001741:Black or African American; D002136:Calcium, Dietary / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D005260:Female; D006304:Health Status; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D015201:Meta-Analysis as Topic; D008875:Middle Aged; D009752:Nutritional Status; D015663:Osteoporosis, Postmenopausal / Q000097:blood* / Q000453:epidemiology*; D010281:Parathyroid Hormone / Q000097:blood*; D017698:Postmenopause / Q000097:blood; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood*
D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D