Our objective was to calculate the time in the sun necessary to maintain existing 25-hydroxyvitamin D (25(OH)D) concentration at locations across Australia and New Zealand. We used a microsimulation model to estimate changes in monthly 25(OH)D concentration using data on standard erythemal dose, solar zenith angle, and climatological ozone. We estimated the number of standard vitamin D doses per 10-min interval and used a dose-response equation to determine the average time in the sun to maintain existing 25(OH)D concentration according to month and time of day. Across all locations in summer, 5-10 min outdoors between 8 a.m. and 4 p.m. on most days of the week, with 35% of the body surface area exposed, is sufficient to maintain existing 25(OH)D concentration. In winter, at mid-to-high latitudes, time outdoors during the middle of the day is required. In winter, with 10% of the body surface area exposed, greater than 45 min in the middle of the day is required in most locations to maintain existing 25(OH)D concentration. These data can be used to inform guidelines regarding maintaining vitamin D via sun exposure and may help health practitioners identify patients who may be vitamin D deficient.
Keywords: 25-hydroxyvitamin D; microsimulation model; standard vitamin D dose; sun exposure.
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