Bone density, body mass, sex hormone relationships clarified
MedWire News: Research into the links between body mass index (BMI) and bone mineral density (BMD) suggests that testosterone, vitamin D, and parathyroid hormone play no part in the relationship.
Various studies have described a clear link between increasing BMI and raised BMD. It has also been suggested that fat mass is inversely linked to fracture risk, however, a protective role for obesity against osteoporosis is far from definite.
For example, as recently reported by MedWire News, researchers in Korea have demonstrated that increases in fat mass are significantly predictive of decreased BMD in premenopausal women only, a relationship the researchers attributed to inflammatory cytokines secreted by adipocytes.
To better understand the interactions between adiposity and bone health, Meinrad Peterlik (Medical University of Vienna, Austria) and team analyzed information collected in a previous study of 1009 Austrian adults drawn from the general population.
As expected, analysis showed that BMI and BMD were significantly related for all skeletal sites tested, with the correlation being stronger in postmenopausal women. Specifically, BMD increased 1.5 times more for each equivalent increase in BMI in post- versus premenopausal women, and 5 times more for each equivalent BMI increase in postmenopausal women versus men.
Interestingly, BMI and levels of β-crosslaps (a marker of bone metabolism) were significantly and inversely correlated in both men and women, "suggesting that inhibition of osteoclastic bone resorption is responsible at least in part for the positive effect of high BMI on BMD," comment the researchers.
Further analysis also revealed that elevated BMI significantly predicted decreased levels of testosterone in men, significant decreases in the vitamin D pre-cursor 25-hydroxyvitamin D (25-[OH]D) in pre- and postmenopausal women, and significant increases in parathyroid hormone in premenopausal women.
Noting that all of the hormonal changes seen would lead to bone loss, the authors write: "Our combined data do not support the assumption that BMI-associated changes in systemic levels of bone active hormones directly mediate the beneficial effect of adiposity on BMD."
"More research is therefore needed to find out whether adipokine and cytokine secretion from adipose tissue could account for the differential osteoprotective effect of adiposity in men and in women before and after menopause," they conclude in the journal Bone.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
By Philip Ford