Working outdoors has been linked to a lower risk of breast cancer among older women in a new study.
Scientists from the Danish Cancer Society Research Center (DCRC) analysed more than 38,000 women under 70 who had been diagnosed with the disease.
Each of these women were compared against five healthy females who were randomly selected from a public register.
Results reveal that among the women over 50, working outdoors for 20 years or more was linked to a 17% reduced risk of a breast cancer diagnosis.
Although unclear, the scientists have speculated being exposed to vitamin D from the sun’s rays may help protect against the disease.
Vitamin D is known to help keep bones and muscles healthy, with emerging research suggesting the so-called sunshine supplement may also ward off cancer and infections.
Concerns about skin tumours, and many people working indoors in offices or retail, mean the vast majority of individuals are spending less time outside.
Around one in eight women in the UK develop breast cancer at some point in their life, usually when over 50, with the disease on the rise worldwide.
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In the US, around 68,000 new breast cancer cases arose in 1970.
By 2014, there was a 242% increase in the disease, despite the US population rising by just 56.8%.
“Thus, the rate of increase in female breast cancer has been more than 4-fold the increase in the US population during the same period,” scientists from St. Joseph’s Hospital in Kentucky wrote in The Linacre Quarterly journal.
Some have suggested this rising incidence may be down to reduced vitamin D exposure, with past research showing higher blood levels of the nutrient is associated with a lower risk of the disease.
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To learn more, the DCRC scientists looked at over 38,000 women with primary breast cancer – a tumour that has not spread beyond the breast or lymph nodes under the arm – from the Danish Cancer Registry.
These were each compared against five healthy women born in the same year from the Danish Civil Registration System.
Employment history was collected from Danish pension fund records, while a woman’s sunlight exposure was calculated via a “job matrix”.
The results, published in the journal Occupational & Environmental Medicine, suggest women over 50 with “occupational exposure” for at least two decades were 17% less likely to be diagnosed with breast cancer.
No link was found among the younger participants or those with a lesser duration of vitamin D exposure.
Although it is unclear how the sunshine supplement could ward off breast cancer, vitamin D has been shown to regulate the genetic expression of cells, as well as cell division and death.
The scientists stressed their study was observational and therefore does not prove cause and effect.
They also did not collect information on vitamin D exposure via supplements or diet, with oily fish like salmon being rich in the nutrient.
Britons cannot absorb a sufficient amount of vitamin D naturally between October and early March.
The NHS therefore recommends adults take a 10 microgram (400 IU) supplement every day.
Although the scientists accounted for some factors like the women’s “reproductive history”, their use of the pill and hormone replacement therapy, as well as alcohol intake, were not adjusted for.
All of these can influence a woman’s breast cancer risk.
Nevertheless, the scientists concluded: “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.”
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