The seasonal importance of serum 25‐hydroxyvitamin D for bone mineral density in older women. (25th September 2016)

• Record Type: Journal Article
• Authors: Michaëlsson, K.; Wolk, A.; Byberg, L.; Mitchell, A.; Mallmin, H.; Melhus, H.
• Is Part Of: Journal of internal medicine. Volume 281:Number 2(2017)
• Page Start: 167
• Page End: 178
• Publication Date: 2016-09-25
• Subjects: 25‐hydroxyvitamin D -- bone mineral density -- season -- vitamin D -- vitamin D intake; Internal medicine -- Periodicals; Medicine -- Periodicals; 616
• DOI: 10.1111/joim.12563
• Languages: English
• ISSNs: 0954-6820

Abstract

Abstract: Background: The impact of season when determining a serum 25‐hydroxyvitamin D (S‐25OHD) cut‐off level for optimal bone health is unknown. Objective: To investigate the relative importance of S‐25OHD for bone mineral density (BMD) by season. Methods: A subcohort of 5002 Swedish women (mean age 68 years), randomly selected from a large population‐based longitudinal cohort study with repeat dietary and lifestyle information, was enrolled during 2003–2009 for a clinical examination, which included dual‐energy X‐ray absorptiometry and collection of fasting blood samples. Categories of vitamin D status were determined by S‐25OHD (measured by HPLC‐MS/MS). Results: In samples collected during summer, we found a gradual increase in BMD of the total hip up to a S‐25OHD level of 40 nmol L −1 (6% of the cohort). In women with S‐25OHD concentrations below 30 nmol L −1 during summer, adjusted BMD was 11% lower [95% confidence interval (CI) 3–19] and in those with S‐25OHD levels of 30–40 nmol L −1 BMD was 6% lower (95% CI 1–11), compared with women with S‐25OHD levels above 80 nmol L −1 . Low S‐25OHD concentrations during summer (<30 nmol L −1 ) were also associated with higher adjusted relative risk of osteoporosis (4.9; 95% CI 2.9–8.4) compared with concentrations above 80 nmol L −1 . By contrast, no differences in mean BMD values between categories of S‐25OHD were found during winter. Conclusions: Summer concentrations of S‐25OHD appear to be the most useful to predict BMD, whereas winter levels have limited value. To determine a S‐25OHD cut‐off level for vitamin D deficiency, it may be necessary to take into account the season of blood collection.