Vitamin D levels low in spring

September marks the start of spring but new research reveals it is also the month when Australians’ vitamin D levels are at its lowest.

The University of Sydney study also shows vitamin D deficiency affects more Australians and lasts longer than previously believed.

“Our results suggest the current guidelines for both vitamin D testing and the use of supplements needs to be reviewed,” Professor Steven Boyages, from Sydney Medical School, said.

Professor Boyages and his PhD student, Kellie Bilinski, recently published their findings in Clinical Endocrinology.

“This is the largest ongoing Australian study on vitamin D deficiency ever undertaken,” Professor Boyages said.

“Vitamin D deficiency is implicated in a number of serious diseases including diabetes and cancer so improving our understanding is critical.”

Previous research has revealed vitamin D plays a vital role in reducing the risk of death associated with older age.

The latest University of Sydney research looked at vitamin D levels (by studying the presence of a metabolite) in more than 24,000 samples taken from walk-in patients and inpatients in NSW between July 2008 and July 2010. It investigated the effect of age, gender, season, socioeconomic status and remoteness on results.

“Our study indicates large segments of the Australian population are at risk of deficiency for prolonged periods of the year, particularly during autumn to the end of spring.

“The prevalence of deficiency was higher and more persistent than previously reported, ranging from 33% in summer to 58% in spring. The seriousness of the deficiency was also greater than in most other Australian reports,” Professor Boyages said.

The study found that vitamin D levels peaked in summer, reaching a maximum in January for women and February for men, before declining gradually in late summer and falling sharply in the winter months. They reached their lowest point not in winter, as previously reported, but in early spring.

“Ideally testing would occur in spring when vitamin D levels reach their lowest concentration. If an individual is found to be deficient a subsequent test three months afterwards would see if they have been able to replenish their vitamin D.

“Similarly use of vitamin D supplements currently fails to address this factor of seasonal variation. A modified approach would see the use of supplements commence, or increase, at the end of summer and be maintained until the end of spring when they would either be stopped or reduced depending on an individual’s sunlight exposure.”