High risk for hip fracture associated with low levels of vitamin D

Low concentrations of serum 25 hydroxyvitamin D are associated with an increased risk for hip fracture, according to recent data.

Researchers from the University of Pittsburgh and other sites in the United States conducted a nested case-controlled study to determine the relationship between low serum 25(OH) vitamin D and hip fractures in women.

The study included 400 participants with incident hip fracture and 400 controls aged between 50 and 79 years. Participants, who were postmenopausal and not taking estrogen or other bone-active therapies, were taken from the Women’s Health Initiative Observational Study. The researchers obtained serum 25(OH) vitamin D levels and followed participants for a median of 7.1 years to evaluate fractures.

Case patients had lower concentrations of serum 25(OH) vitamin D, compared with controls (55.95 nmol/L vs. 59.6 nmol/L; P=.007). The risk for hip fractures increased with lower vitamin D concentrations (OR for each 25 nmol/L decrease=1.33; 95% CI, 1.06-1.68).

Compared with women with the highest concentrations (≥70.7 nmol/L), those with the lowest (≤47.5 nmol/L) had a higher risk for hip fracture (OR=1.71; 95% CI, 1.05-2.79), which increased across quartiles of serum 25(OH) vitamin D concentration (P=.016). – by Stacey L. Adams

Ann Intern Med. 2008;149:242-250.

This study does not really provide any new insight into fracture risk. Low vitamin D levels lead to secondary hyperparathyroidism (a rise in parathyroid hormone level due to a vitamin D deficiency mediated fall in calcium.) Parathyroid hormone increases bone turnover in part to stabilize serum calcium, and this increased bone activity leads to disrupted microarchitecture of bone, the brick wall arrangement in hips (cortical bone) and the flying buttress (Notre Dame) arrangement in spine (trabecular bone). This is not new information. In fact, the report did not measure parathyroid hormone but did measure bone collagen, a marker for bone activity (turnover) and this bone collagen rise, reflecting the bone turnover, really accounted for the correlation of vitamin D deficiency and fracture risk. So although this report does not break any new ground, the study underscores the fact that people who are vitamin D deficient will fracture, and vitamin D and calcium must be replaced, otherwise medical intervention (such as a bisphosphonates) will be less effective. For that reason alone (reminding the physician to check vitamin D and calcium intake) the study serves a purpose.

– Donald Bergman, MD

Endocrine Today Editorial Board member