Estimates of beneficial and harmful sun exposure times during the year for major Australian population centres.

To examine the influence of geographical and seasonal factors on duration of solar ultraviolet (UV) radiation exposure of skin to produce recommended vitamin D levels without producing erythema. An ecological study using daily Ultraviolet Index (UVI) data collected in major population centres across Australia for 1 year (1 January - 31 December 2001) to calculate sun exposure times for recommended vitamin D production and erythema. Sun exposure times to produce either serum vitamin D concentrations equivalent to an oral intake of 200-600 IU/day or erythema for people aged 19-50 years with fair skin (Fitzpatrick type II skin) exposing 15% of the body. In January, across Australia, 2-14 minutes of sun three to four times per week at 12:00 is sufficient to ensure recommended vitamin D production in fair-skinned people with 15% of the body exposed. However, erythema can occur in as little as 8 minutes. By contrast, at 10:00 and 15:00, there is a greater difference between exposure time to produce erythema and that to produce recommended vitamin D levels, thereby reducing the risk of sunburn from overexposure. From October to March, around 10-15 minutes of sun exposure at around 10:00 or 15:00 three to four times per week should be enough for fair-skinned people across Australia to produce recommended vitamin D levels. Longer exposure times are needed from April to September, particularly in southern regions of Australia. Our study reinforces the importance of existing sun protection messages for the summer months throughout Australia. However, fair-skinned people should be able to obtain sufficient vitamin D from short periods of unprotected sun exposure of the face, arms and hands outside of the peak UV period (10:00-15:00) throughout Australia for most of the year. The greater variability in sun exposure times during winter, means that optimal sun exposure advice should be tailored to each location.