Summer concentrations of 25OHD predict bone mineral density

(HealthDay)—Summer levels of serum 25-hydroxyvitamin D (S-25OHD) are associated with bone mineral density of the total hip, according to a study published online Sept. 25 in the Journal of Internal Medicine.

Karl Michaëlsson, M.D., from Uppsala University in Sweden, and colleagues examined the relative importance of S-25OHD for bone mineral density by season in a subcohort of 5,002 Swedish women randomly selected from a large population-based cohort.

The researchers found that there was a gradual increase in bone mineral density of the total hip in samples collected during summer, up to an S-25OHD level of 40 nmol L⁻¹. Compared to those with S-25OHD levels above 80 nmol L⁻¹, adjusted bone mineral density was 11 percent lower in women with S-25OHD concentrations below 30 nmol L⁻¹ and 6 percent lower in those with S-25OHD concentrations 30 to 40 nmol L⁻¹ during summer. Compared with concentrations above 80 nmol L⁻¹, low S-25OHD concentrations (<30 nmol L⁻¹) during summer correlated with increased adjusted relative risk of osteoporosis. There were no differences in mean bone mineral density values between categories of S-25OHD in winter.

"To determine an S-25OHD cut-off level for vitamin D deficiency, it may be necessary to take into account the season of blood collection," the authors write.