More vitamin D needed to prevent osteoporosis in seniors – May 2010

Age but not Gender Modulates the Relationship between PTH and Vitamin D

Bone. 2010 May 6. Epub ahead of print Arabi A, Baddoura R, El-Rassi R, Fuleihan GE.
Calcium Metabolism and Osteoporosis Program, Department of Internal Medicine, American University of Beirut, Beirut, Lebanon; Department of Rheumatology, Saint Joseph University, Beirut, Lebanon.

CONTEXT: It is unclear whether the relationship between 25-OHD and PTH is modulated by age or gender.
OBJECTIVE: To assess the 25-OHD-PTH relationship in 340 adolescents (10-17years) and 443 elderly (65-85years) of the same ethnic group, and living in the same sunny country.
ASSESSMENTS: Calcium intake was estimated. Serum calcium, phosphorus, 25-OHD and PTH were measured. Body fat was determined by DXA.
RESULTS: 25-OHD levels were lower in the elderly in the overall group (p<0.001) and within genders. 25-OHD levels were lower in females in the overall group and within age sub-groups (p<0.05). PTH levels were higher in the elderly in the overall population and in both genders (p<0.001). There were no gender differences in PTH levels within age sub-groups. For the same 25-OHD level, PTH levels were comparable across genders but were 1.5-2 folds higher in the elderly compared to adolescents (p<0.001).
PTH correlated positively with age (p<0.001), body fat (p=0.02), and negatively with calcium intake (p<0.001), and 25-OHD (p<0.001). The magnitude of the correlation with 25-OHD decreased after adjustment for age but not for gender. In multivariate analyses, age, 25-OHD and fat mass were independent predictors for PTH. In the elderly, after adjustment for serum creatinine, only 25-OHD and creatinine were independent predictors of PTH.

CONCLUSION: The negative relationship between 25-OHD and PTH is modulated by age but not gender. Desirable 25-OHD levels derived from examining the 25-OHD-PTH relationship should therefore take into account the age of the population of interest. Copyright © 2010. Published by Elsevier Inc. PMID: 20452474

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