Target levels of vitamin D need to allow for seasonal variation

DOCTORS should allow for a winter drop in vitamin D levels when assessing the status of patients in summer, experts say.

An updated position statement from the Australian and New Zealand Bone and Mineral Society (ANZBMS) and Osteoporosis Australia recommends a serum 25-hydroxyvitamin D level of more than 50 nmol/L at the end of winter. A level 10 to 20nmol/L higher at the end of summer is required for optimal musculoskeletal health.

Former president of the ANZBMS, Professor Rebecca Mason, said the need to allow for a winter drop was far more important than a possible rise in target levels in the future.

“There is a need to allow for a winter drop in vitamin D when assessing levels in summer and there is increasing evidence that at some future time we
may have enough evidence to suggest that the target guidelines might be higher,” Professor Mason told MO.

People with moderately fair skin can maintain adequate levels in summer by walking outside with arms exposed for six to seven minutes mid-morning or mid-afternoon on most days, according to the statement, published in the Medical Journal of Australia (MJA). People with dark skin need three to six times more sun exposure.

The statement acknowledged achieving this was more difficult in winter when noon was the only time there was sufficient UVB radiation to produce vitamin D in many parts of the country. Up to 40 minutes was required, to maintain levels, it said.

Screening is recommended for those at risk of deficiency, such as disabled people, dark-skinned people and those working indoors, followed by supplementation, if required. The statement said supplementation without screening may be appropriate in some groups, such as dark-skinned migrants.

The authors cautioned that vitamin D supplementation may be more appropriate than sun exposure for people at high risk of skin cancer.

The update does not address vitamin D in pregnancy.

Professor Mason said a separate position paper covering pregnancy, infants, children and teenagers was undergoing minor revisions and would be submitted to the MJA.
Med J Aust 2012; 196:686–87