UV Doses of Americans¶

Abstract

The UV doses of Americans were never measured, but are needed for assessing the risks of UV-related health effects. We calculated these doses using a novel approach. The Environmental Protection Agency's (EPA) National Human Activity Pattern Survey (NHAPS) recorded the activity profiles of 9386 Americans over 24 months to assess their exposure to environmental pollutants, one of which is UV radiation. NHAPS used randomized telephone interviews to get their previous day's minute-byminute activities. From NHAPS we extracted only the outdoor-daylight data of the northern and southern indoor workers (95%), stratifying by season, sex and age (0-21, 22-40, 41-59 and 60؉ years) to find the average time Americans spend outdoors. Knowing the total daylight time and that while outdoors Americans are exposed to about 30% of the available solar UV (on a horizontal plane), we calculated their percent ambients. The average American's percent ambients are 2.6 and 2.5% for northern and southern females, respectively, and 3.5 and 3.6% for northern and southern males, respectively. Men over 40 years of age have the highest ambients (4%). From their ambients we calculated their annual doses using seasonal averages of UV measurements taken daily for over 2 years by EPA Brewer spectrophotometers located in four quadrants of the United States: Atlanta, GA; Boston, MA; Bozeman, MT and Riverside, CA. The average erythemal UV doses of Americans are about 25 000 J/m 2 /year, 22 000 for females and 28 000 for males, or 33 000 J/m 2 /year including a conservative continental U.S. vacation (7800 J/m 2 ). Thus, we can now assess the risks of UV-related health effects for Americans.

The relationship between ambient ultraviolet radiation (UVR) and objectively measured personal UVR exposure dose is modified by season and latitude

“…9,10 The strong seasonal effect on this fraction has also been reported in other studies. 28,29 In an earlier study in subtropical Australia, the personal exposure fraction in winter was found to be more than twice the fraction in summer (6.5% vs. 2.7%).…”

Ultraviolet radiation exposure pattern in winter compared with summer based on time-stamped personal dosimeter readings

“…In addition, we collected UV exposure data from 28 Danish volunteers (13 males and 15 females), median age 39 years (range 4-70) visiting popular sunny holiday resorts in the winter half-year for a median of 7 days (range [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. These subjects were indoor workers from the staff of the department or family or friends of the staff.…”

“…In the continental U.S.A. covering the latitudes 33-45°N, the annual UV doses of Americans were recently estimated based on daily outdoor activity profiles and ambient UV measurements. [1][2][3] These studies are based on the assumption that the same percentage (30%) of terrestrial UV radiation is available for solar exposure during the whole year round. An Australian study examined the annual occupational exposure of outdoor workers to UV radiation (23AE5°S) by personal dosimetry, but did not measure the recreational exposure or the exposure of indoor workers.…”

Sunlight, tanning booths, and vitamin D

“…In a study of the activity profile of over 9000 individuals in the United States over 24 months, it has been estimated that the average UV doses these subjects were exposed to was 25,000 J/m 2 per year. 65 A study of 3449 Canadian adults ([25 years old) reported that 51% of the subjects were exposed to daily sunlight for a duration of between 30 minutes and 2 hours, and 26% were exposed for more than 2 hours. 66 Using personal digital dosimeters, studies in 4 high school students in the New York metropolitan area showed that the average UVB exposure was enough to cause erythema in fair-skinned students.…”

“…51,84 However, studies on duration or dose of incidental sun exposure indicated that subjects had more that adequate sun-exposure time or UV dose needed for the current recommended vitamin D level. [64][65][66][67][68][69] The reason(s) for the lack of correlation between these two sets of studies remains to be clarified. Artificial sources of UV vary tremendously in the amount of UVB they contain, and the consumer of that radiation cannot determine that amount from examining these devices.…”