Working outdoors could lower an older woman’s risk of breast cancer, possibly because of vitamin D exposure, according to new Danish research published today.
Although evidence about high levels of vitamin D being associated with a reduced risk of breast cancer is inconclusive, most studies have relied on limited assessments of vitamin D levels rather than looking at levels over the long term.
Researchers from the Danish Cancer Society Research Centre write in Occupational & Environmental Medicine that their findings from an observational study suggest outdoor workers are exposed to more sunlight, which boosts their levels of vitamin D, thus protecting them against the disease.
They identified 38,375 women under the age of 70 who had been diagnosed with primary breast cancer from the Danish Cancer Registry and compared each of them with five women born in the same year, randomly selected from the Danish Civil Registration System.
Full employment history was retrieved from Danish pension fund records and the team completed a job exposure matrix to assess each woman’s occupational exposure to sunlight.
While no association was found between occupational exposure to sunlight and overall breast cancer risk, long-term occupational exposure was associated with a lower risk of breast cancer after the age of 50.
In these women, they found occupational exposure for 20 or more years was associated with 17% lower risk of a breast cancer diagnosis, while the highest level of cumulative exposure was associated with 11% reduced odds.
Although there were some limitations to the study, such as a lack of information on dietary vitamin D intake or use of vitamin D supplements, crude estimates about sunlight exposure, and no accounting for potentially influential lifestyle factors, such as use of the Pill, hormone replacement therapy, and alcohol, as well as obesity and leisure time physical activity, they say their findings merit further investigation.
“This study indicates an inverse association between long-term occupational [sunlight] exposure and late-onset breast cancer. This finding needs further attention in future occupational studies,” they write.
Pederson JE, Strandberg-Larsen K, Andersson M et al. Occupational exposure to solar ultraviolet B radiation and risk of subtypes of breast cancer in Danish women. Occupational & Environmental Medicine 2 February 2021
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