RESEARCH - Responses of parathyroid hormone to vitamin D supplementation

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Arch Gerontol Geriatr. 2008 Feb 1 [Epub ahead of print]

Responses of parathyroid hormone to vitamin D supplementation: A

systematic review of clinical trials.

Björkman M, Sorva A, Tilvis R.

Clinics of Internal Medicine and Geriatrics, Helsinki University

Central Hospital, POB 340, FI-00290 HUS, Helsinki, Finland.

The beneficial bone effects of vitamin D supplementation have been

attributed to suppression of secondary hyperparathyroidism by

25-hydroxyvitamin D (25-OHD) levels at least 50nmol/l. In this

systematic review, we have analyzed the results of 52 clinical trials,

including 72 intervention groups and 6290 patients, on vitamin D

supplementation in order to evaluate the experimental evidence and the

effects of age and chronic immobility on responses of parathyroid

hormone (PTH). The papers for this systematic review were selected

through a search in PubMed and through a review of the reference lists

of articles. Negative logarithmic (R(2)=0.318, p<0.001) and linear

(R(2)=0.294, p<0.001) correlations were found between 25-OHD and PTH

levels, when all pre- and post-trial values were scattered. Negative

linear (R(2)=0.385, p<0.001) and logarithmic (R(2)=0.406, p<0.001)

correlations were also found between the changes in 25-OHD and PTH

levels. Age correlated negatively with changes in PTH (r=-0.476,

p<0.001). The vitamin D supplementation of the chronically immobile

patients resulted in a smaller decrease in PTH levels (-8.4 vs.

-17.4%, p<0.001) despite a larger increase in 25-OHD levels (187.2%

vs. 109.8%, p<0.001). According to the multiple regression analysis

the changes in PTH were independently predicted by pre-trial PTH,

changes in 25-OHD, age and chronic immobility, explaining 53.2%

(R(2)=0.532) of the variation. This meta-analysis shows that responses

of PTH to vitamin D supplementation are not only determined by the

baseline PTH levels and changes in vitamin D status, but also by age

and mobility of the patients. Our results also suggest that PTH

decreases quite linearly during vitamin D supplementation at any given

25-OHD level. Longitudinal vitamin D supplementation studies on

populations with wide range of mobility and age are needed to further

elucidate their confounding effects. In determining the sufficient

doses of vitamin D supplementation and adequate 25-OHD levels, these

confounding effects and the inter-individual variation in responses of

PTH to vitamin D supplementation should be taken into account.

PMID: 18243368

http://www.ncbi.nlm.nih.gov/pubmed/18243368

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