Endocrine Abstracts

Objective: To determine whether there is a seasonal variation in bone mineral density (BMD) related to exposure to sunlight.

Design: A single-centre retrospective analysis of BMD measurements.

Participants: Of 10 971 patients who had undergone bone densitometry in the period 2000–2007. 7513 were female and 3458 male.

Results: Anonymised data on BMD of lumbar spine was gathered from existing hospital databases. Climate data for the region was obtained from the Met Office for the period of interest. Hours of sunshine per day showed the expected, approximately sinusoidal variation throughout the year.

To investigate periodicity in the BMD data, the densitometry results were grouped by date of scan which was converted into ‘solar day’ – the number of days from the winter solstice. The mean and median BMD were then plotted versus solar day. There was no observable seasonal variation in BMD displayed. This analysis was repeated for several sub-groups (on the basis of sex, age and source of referral), which consistently failed to show seasonal variation in BMD.

A further analysis employing Fourier transforms was applied to the data in an attempt to detect underlying periodicity which had been obscured by ‘noise’ in the original analysis. This also failed to demonstrate seasonal variation in BMD.

Conclusions: This study has failed to demonstrate a seasonal variation in BMD. Further study of the relationship between sunlight exposure, biochemistry and bone mineral density is warranted.