Australians are most vitamin D deficient in September

Vitamin D deficiency among Australians is more prevalent and lasts longer than expected, says a new study.

To determine the prevalence of vitamin D deficiency in Australia, the epidemiological study measured vitamin D concentrations in 24,819 blood samples between July 2008 and July 2010 (1). The study results showed that the participants were most deficient (less than 50 nanomoles vitamin D per liter serum) during fall and spring, especially in September (58% of total participants). Vitamin D levels were highest during the summer, peaking for women in January and men in February with a total of 36% people who were vitamin D deficient. The highest prevalence of deficiency occurred in female inpatients (42% in summer and 62% in spring). Additional factors associated with lower vitamin D included being an inpatient, female, aged 20–39 or over 79 years, being socioeconomically disadvantaged or from a major city.

The researchers concluded that the use of vitamin D supplements do not currently address the factor of seasonal variation. A modified approach would include commencement, or increase, of supplement use at the end of summer and be maintained until the end of spring, at which time the supplement use would either be stopped or reduced depending on an individual's exposure to sunlight. Thus, supplementation guidelines would need to be modified and strengthened.

1. Boyages, S. et al. Seasonal reduction in vitamin D level persists into spring in NSW Australia: implications for monitoring and replacement therapy. Clinical Endocrinology. Published online September 2012.