Human Exposure

In studies of school children's exposure to UV, boys usually have greater exposure than girls (Melville et al., 1991; Ono et al., 2005). Methods of surveying school children for their exposure were recently described (Ono et al., 2005). One reported trend in U.S. elementary schools is the elimination of outdoor recess (DeGregory, 2005), which would remove the option for significant sun exposure for most children for five days of the week during the school year. Policies for outside time vary widely at different schools, ranging from a school in Arizona where on all days without rain, 1st and 2nd graders had outside recess morning and afternoon, during lunch, plus outside physical education twice a week (Sharon Harlan, pers. comm., July 2005), to some inner city Baltimore schools where outside time is unusual (Janie Gordon, pers. comm., 2007), to some Atlanta, GA schools that are being built without outside playgrounds (DeGregory, 2005). Some public schools insist on students wearing hats or sunscreen for outdoor activities whereas others, even in sunny climates, have no such policy (Sharon Harlan, pers. comm., July 2005)

For those schools that do have outside play areas, another recent development pertinent to UV effects on health is the movement to "green school yards, which will most likely lead to greater tree cover and shading of students. The magnitude of this movement is made evident by a search of the internet using the index words "school yard greening," which receives many hits. This raises the issue of the degree to which UV shading is considered in these programs and the guidance that is available for planning and design for UV modification.

Protection of children during the school day is of special concern in Australia and New Zealand because of the large proportion of fair-skinned individuals in the population and the fact that UV irradiance tends to be higher than in equivalent northern latitudes (Gies and Mackay, 2004; Wright et al., 2007). Though there has been some success with inculcating sun protective behaviors in youth in Australia, the provision of shade structures for school yards has been recommended for additional protection (Moise et al., 1999; Gies and Mackay, 2004). The general suggestion in Australia is that these shade structures should provide a UV protection factor (PF = UV in open/UV transmitted) of 15 for "all-day" protection, although a PF of 4 to 8 would be sufficient over the noon hour (Gies and Mackay, 2004). Many structures that have been built at schools, (i.e., verandahs and pavilions) provided PF of at least a 4 to 8 range (Gies and Mackay, 2004). A higher PF could be obtained by adding trees or vines along the open sides of these structures. For tree shade alone, PF could vary widely, ranging from a value of 1.6 for a small-crowned single tree in the open blocking only 20% of sky view (Grant, 1997) to a value of 46 for tree shade in the school-yard study of Gies and MacKay (2004).

Several epidemiological studies (Garland et al., 1990; Grant, 2003) have found that the relationship between solar radiation in a region and the subsequent risk reductions for non-cutaneous cancers is stronger for rural residents than for urban residents. It has been suggested that this is a function of lifestyle differences

(Garland et al., 1990; Grant, 2003). However, more study seems necessary as an alternative hypothesis states that an urban atmosphere may sufficiently reduce UV-B radiation to reduce the benefit of UV-B radiation for adequate vitamin D production.

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