Vitamin D deficiency, supplementation and testing: have we got it right in New Zealand?

BACKGROUND

Severe prolonged vitamin D deficiency can cause rickets or osteomalacia. Both can be prevented by sunshine exposure or vitamin D supplementation. Although New Zealand guidance does not recommend vitamin D supplementation for the general population, it can be considered for individuals at risk of vitamin D deficiency. Routine measurement of 25-hydroxyvitamin D (25OHD) is also considered unnecessary.

METHODS

We investigated the rates of vitamin D supplementation, rickets and osteomalacia in New Zealand, and of 25OHD results in Auckland, over the last two decades.

RESULTS

Vitamin D prescriptions increased 14-fold, from 86,295/year to 1,215,507/year, between 2003 and 2019, with medication costs alone in 2019 being >$1 million. Despite these changes, the annual prevalence of hospital admissions for rickets, osteomalacia and unspecified vitamin D deficiency remained low and stable (10-20/year). 25OHD concentrations increased between 2002 and 2003 and between 2009 and 2019, and in the later time-period, 25OHD tests mainly identified individuals without vitamin D deficiency (40-50% >75nmol/L, 65-70% >50nmol/L and only 7-12.5% <25nmol/L).

CONCLUSIONS

Osteomalacia and rickets persist at low rates despite widespread, increasingly costly vitamin D supplementation and testing, which largely identifies individuals without vitamin D deficiency. These results suggest that vitamin D guidance and practice in New Zealand should change.