Serum Vitamin D Levels in Office Workers in a Subtropical Climate

Vitamin D is necessary to maintain healthy bones, and may prevent other chronic diseases. There is limited information regarding the vitamin D status of people living in climates with relatively high ambient ultraviolet radiation. We therefore aimed to determine serum 25(OH) D levels in a group of office-workers in subtropical Australia. We collected blood from 129 office workers in summer (n = 129) and 175 in winter (91 in both seasons). Serum 25(OH) D was estimated using a commercial chemiluminescent immunoassay and we asked participants to complete questionnaires about sun exposure and diet for the month prior to blood collection. Summer and winter mean serum 25(OH) D was 74 (95% CI 70-77) nmol L-1 and 54 (95% CI 51-57) nmol L-1, respectively. In summer, 14% of participants were classed as insufficient, compared with 51% in winter. High 25(OH) D levels in summer were associated with time spent outdoors in nonpeak UV periods, while in winter high levels were associated with intake of vitamin D from food or supplements. The high prevalence of vitamin D insufficiency observed in this population highlights the need for further examination of the relation between sunlight and vitamin D production to enable more accurate sun exposure recommendations.