Vitamin D insufficiency in New Zealanders during the winter is associated with higher parathyroid hormone concentrations: implications for bone health?
BACKGROUND
Parathyroid hormone concentration (PTH) is elevated in vitamin D insufficiency and when prolonged, this condition leads to reduced bone mass and possibly osteoporosis. The threshold of 25-hydroxyvitamin D above which PTH plateaus, is a criterion often used to define vitamin D adequacy.


OBJECTIVE
To determine whether the higher rates of vitamin D inadequacy reported in the winter than summer months in New Zealand also result in higher PTH concentrations. Also to explore the relationship between 25-hydroxyvitamin D and PTH concentrations in a New Zealand population to determine if a threshold exists for plasma 25-hydroxyvitamin D concentration.


METHODS
Plasma 25-hydroxyvitamin D and PTH concentrations were determined in 342 volunteers living in Invercargill and Dunedin (latitude 45-46 degrees S) in late summer (February) and early spring (October).


RESULTS
Mean plasma 25-hydroxyvitamin D concentration was higher in the late summer versus early spring (79 vs 51 nmol/L; p<0.001). The lower plasma 25-hydroxyvitamin D in early spring versus summer was associated with a 0.2 pmol/L (p<0.001) higher PTH concentration. A threshold of 61 nmol/L was estimated for plasma 25-hydroxyvitamin D, above which there was no further decrease in PTH concentration.


CONCLUSIONS
The higher PTH concentration in winter than summer suggests that the low 25-hydroxyvitamin D concentration in the winter months may be having an adverse effect on bone health. Many New Zealanders have 25-hydroxyvitamin D concentrations less than 62 nmol/L, especially in winter. Strategies to improve the vitamin D status of the population such as supplementation and food fortification may be needed.
Rockell
Jennifer E P
JE
Department of Human Nutrition, University of Otago, Dunedin.
Skeaff
C Murray
CM
Venn
Bernard J
BJ
Williams
Sheila M
SM
Green
Tim J
TJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D010281:Parathyroid Hormone / Q000097:blood*; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000453:epidemiology*; D055815:Young Adult
D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D