Written by Joyce Smith, BS. This study found that occupational UVR exposure may only slightly diminish the risk of breast cancer after the age of fifty.
Previous epidemiological studies have indicated that solar ultraviolet B radiation (UVR) may have a protective effect on breast cancer. However, the evidence remains inconclusive. Only one study found an increased risk of breast cancers in geographical areas of higher sunlight exposure 1 but showed no increased risk of hormonal cancers for women over fifty years of age. There is substantial evidence that higher vitamin D levels may lessen cancer risk through their anticarcinogenic properties that affect cell proliferation, angiogenesis, cell differentiation and apoptosis 2. Other mechanisms such as increased night time melatonin is also protective against cell proliferation. A study on self-reported time spent outdoors was inversely associated with cancer risk 3 and subject to recall bias. Since outdoor work history and information on lifetime employment have not been previously studied, the present study explores the association between occupational UVR exposure and breast cancer using objective information on lifetime employment which is more accurate than self-reporting.
In a large-scale, population-based, case-control study 4, researchers identified 38, 375 women under the age of 70 who had been diagnosed with primary breast cancer from the Danish Cancer Registry. They compared each woman with five cancer-free women born in the same year and randomly selected from the Danish Civil Registration System. Full employment history was retrieved from Danish pension fund records and a job exposure matrix was used to assess each woman’s occupational exposure to sunlight.
After accounting for potential confounders such as reproductive history, researchers found no association between occupational exposure to sunlight and overall breast cancer risk. Occupational UVR exposure was inversely associated with risk only for participants older than 50 years who were exposed to UVR for 20 years or longer (≥20 years: OR=0.83, 95% CI 0.75 to 0.92) and who had acquired the highest cumulative UVR exposure (OR=0.89, 95% CI 0.83 to 0.95). For those women, occupational exposure over 20 years reduced the odds of breast cancer diagnosis by 17%, while the highest levels of cumulative exposure were associated with an 11% reduction. Estrogen receptor status did not appear to influence breast cancer risk.
These study has several limitations. Information on lifestyle factors, including use of oral contraceptives, hormone replacement therapy, obesity, alcohol consumption and physical inactivity, was not available and may thus have confounded results. Dietary vitamin D intake and supplementation, both important sources of vitamin D, were not accounted for. Increased skin pigmentation and the liberal use of sunscreens were also not considered. A sunscreen protection of 15 absorbs 99% of UVB radiation 3. Employment data from the ATP registry 5 did not include self-employed women such as those in the farming industry; therefore, a large group may have been underestimated. Also, individual s whose accumulated UVR exposure reflected both indoor and outdoor jobs and self-reported leisure time spent outdoors were not accurately assessed which may have skewed UVR exposure assessments and led to misclassifications 6,7. However, this is the first study to explore the association between occupational UVR exposure and breast cancer using an objective lifetime employment history, which more accurately measures UVR exposure than cross-sectional ambient measures and eliminates the bias of self-reporting. Future studies are needed to confirm the association.
Source: Pedersen, Julie Elbaek, Katrine Strandberg-Larsen, Michael Andersson, and Johnni Hansen. “Occupational exposure to solar ultraviolet B radiation and risk of subtypes of breast cancer in Danish women.” Occupational and Environmental Medicine (2021).
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Posted February 16, 2021.
Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.
References:
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- Pedersen JE, Strandberg-Larsen K, Andersson M, Hansen J. Occupational exposure to solar ultraviolet B radiation and risk of subtypes of breast cancer in Danish women. Occup Environ Med. 2021.
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