Vitamin D status of psychiatric inpatients in New Zealand's Waikato region

Background: Vitamin D deficiency is widespread in New Zealand, confers multiple health risks, and may be particularly common among people with psychiatric illness. We studied vitamin D status in an unselected sample of adult psychiatric inpatients in Hamilton (latitude 37.5 S) during late winter. Methods: We recruited 102 consenting subjects and measured 25-hydroxy vitamin D3 levels in venous blood using a competitive electrochemiluminescence immunoassay. In addition to descriptive statistics, we used one-sample t-tests to determine the extent to which ethnic and diagnostic subgroups fell below the vitamin D deficiency threshold of 50 nM. Results: 75 subjects (74%) had vitamin D levels < 50 nM and thus had at least mild deficiency, while 19 (19%) were severely deficient with levels < 25 nM. Rates of deficiency were comparable for men and women; only the former showed a correlation of vitamin D levels with age (r = 0.45, p < 0.01). Maori participants constituted half the sample (n = 51) and were more likely to be deficient than their European counterparts (p = 0.04). Vitamin D also varied by diagnosis, with schizophrenia associated with markedly lower levels than mania and depression (p < 0.001). Conclusions: Vitamin D deficiency is prevalent in the psychiatric inpatient setting in New Zealand and may be relevant to poor physical health outcomes, notably among Maori and those with schizophrenia. These findings support proposals to provide vitamin D supplementation, particularly during the winter months.