Working the night shift can cause cancer in women?

If working nights wasn’t stressful enough for everyone, now there’s research that shows working at nights may lead to higher instances of breast cancer in women.

I work with a few ladies at night (our usual schedule) so this news, while it’s been the talk almost every time we meet, is most certainly not welcome. The research pertains to the Danish military in which 18,500 women who served between 1964 – 1999 and 141 had developed breast cancer by 2005 – 2006.

Most surprising, though, was the fact that women who worked night shifts and described themselves as being “morning” people — that is, they preferred to wake up early, rather than stay up late at night — had a four times higher risk of breast cancer than women who worked during the day. “The four times higher increased risk surprised us. It was very unusual,” says Hansen.

This is also the case with almost everyone I work with, not just women. I’m one of the few there that are actual night owls and the rest are the “normal” folks who work because that’s just part of the job and otherwise would rather be enjoying daylight.

There were grumbles of this previously when they looked at nurses who worked the night shift and considered other parameters besides just lack of direct Sun.

The nurse studies had pointed toward a possible explanation for the association: because night workers labor under artificial light, they may be exposed to less natural sunlight and, therefore, less vitamin D from the sun’s rays than day workers; lower levels of vitamin D have been linked to increased risk of breast cancer. Based on the questionnaires, however, Hansen found that the Danish night workers actually spent more time outdoors and had higher rates of sun exposure than day workers, since they were free during the day when others were indoors at work.

I know that at least three are mothers who spend time with their children during the day, outdoors a lot of times. This is most distressing and if it can be corroborated outside the Danish military, we’ll have to rethink the true cost of working at night. However the two other women in the “night owl” category may be spared this danger.

Genes may also play a role, since whether a person is a “night owl or a “lark” is partially determined by his or her genetic makeup. Hansen’s finding that shift work can be particularly risky for “larks,” people who are more alert and active in the morning than at night, makes sense, since genetics may make it harder for a morning person to adjust to hormonal and metabolic changes that come with working at night. “It’s much worse to be a morning person and have night shift work when it comes to breast cancer,” says Hansen.

I hope the vitamins I see a lot of the “larks” taking are compensating for this at least somewhat.


This post previously had “18,500 women who served between 1964 – 1999 and had developed breast cancer”, which is incorrect (very, very incorrect).
Changed to “18,500 women who served between 1964 – 1999 and 141 had developed breast cancer”.