Functional hypoparathyroidism ‘does not protect bone’
MedWire News: Bone mineral density (BMD) is not influenced by the presence of functional hypoparathyroidism, a study of postmenopausal women with fragility fractures indicates.
The data do not support the hypothesis that functional hypoparathyroidism has a protective role on bone status, say Thierry Thomas (University Hospital of Saint-Étienne, France) and colleagues writing in Joint Bone Spine.
Functional hypoparathyroidism - characterized by vitamin D insufficiency but without secondary hyperparathyroidism - has been proposed to have a paradoxical protective influence on bone health, due to the lack of compensatory but deleterious mechanisms of this metabolic profile.
"Indeed, functional hypoparathyroidism has been associated with higher total hip BMD compared to secondary hyperparathyroidism," Thomas et al remark.
To investigate further, the team studied 237 women (mean age 72.9 years) admitted between 2003 and 2007 with a low-energy fracture of the wrist, humeral, or femoral upper extremity.
Vitamin D insufficiency (VDI), defined as a 25-hydroxyvitamin D (25[OH]D) level of 30 ng/mL or less, was present in 214 women, or 90.4% of the cohort.
Despite the high prevalence of VDI, however, 87.9% of women had normal levels of parathyroid hormone (PTH), defined as a serum intact PTH level of 64 ng/L or less.
Indeed, within the subgroup of women with VDI, there was no PTH "plateau" level that was related to 25(OH)D, Thomas and co-authors note.
They then repeated their analyses using a more stringent definition of VDI, set at a 25(OH)D level of 15 ng/mL or less.
Using the revised definition, they found that hip BMD was significantly lower in women with VDI than in those without VDI; however, the vast majority (81.2%) of people with VDI still had normal PTH levels. Furthermore, BMD was unrelated to whether or not PTH levels were normal or raised.
Thomas et al conclude: "Overall, our data do not support the hypothesis that this profile has protective effects on bone. Further studies in larger elderly populations including patients without fragility fracture, should more definitely address this important question for clinical practice."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012
By Joanna Lyford