Endocrine Abstracts

Introduction: The vitamin D (25OHD) status of a population will reflect genetic and environmental factors. We evaluated all 25OHD assays undertaken at a regional centre in an area at high risk of vitamin D deficiency, over a 10 year period on the basis that this would provide insight into annual, seasonal and age based trends in 25OHD status. We planned to correlate vitamin D measurement with trends in vitamin D prescribing.

Methods: Data (66 694 samples) from a 10 year period (2002–2011) were collected from the regional biochemistry department. Age, gender, month of sampling and 25OHD status were obtained and the average sunshine hours/month for Northern England obtained via the Meteorological Office. Local prescribing data were obtained from the pharmacy department. Regression and time series analyses were performed.

Results: There was a near ten-fold increase in 25OHD assay requests from 2170 (2002) to 19 954 (2011) and a concomitant rise in prescriptions. This pattern also applied to the paediatric population (P<0.01). 25OHD levels fell year by year despite the change in vitamin D prescriptions. Seasonal analysis showed peak vitamin D levels from Jul to Aug and nadir levels from Jan to Mar. There was a significant relationship between mean 25OHD levels and mean sunshine hours (r=0.51, P<0.01). In the 0–20 year group there was a decrease in 25OHD levels with age with a nadir at 13–17 years (ANOVA, P<0.01).

Conclusions: The number of vitamin D analyses and prescriptions has increased steadily over the last decade. Vitamin D levels in the population follow a seasonal trend which is strongly dependent on sunlight exposure. There has been a downward trend in 25OHD levels which could reflect several factors including increased testing in a rising ethnic minority population. Vitamin D levels fall from birth with a nadir during puberty, possibly due to the increased conversion of 25OHD to 1,25OHD to meet increased skeletal demands.