If you're a night owl but decided to work a day shift because of the possibility of developing breast cancer while working during the night, it's time you reconsidered that.

An assessment back in 2007 suggested that the effect of night shift work on the body is probably carcinogenic, influencing the incidence of breast cancer in women. However, data from three recent studies and a review published in the Journal of the National Cancer Institute show that, on the contrary, night shifts have little or no influence on the occurrence of breast cancer.

Ruth Travis and colleagues from the Cancer Epidemiology Unit at Oxford University followed 800,000 women in their three large-scale UK studies. The purpose of the researches was to examine and identify the risks of night shift work. The three studies involved 522,246 participants in the Million Women Study, another 22,559 women who participated in the EPIC-Oxford study and 251,045 UK Biobank volunteers.

The subjects answered questions regarding their shift work, then they were followed for incident cancer. There was no increased risk of breast cancer development due to working at night, not even long-term night shifts, according to these studies.

The study was funded by the UK Health and Safety Executive, along with Cancer Research UK and the UK Medical Research Council, and it analyzed data from 10 separate previous researches conducted in the UK, the United States, China, Sweden and the Netherlands.

The researchers compared breast cancer risks for women who didn't work night shifts to women who did for long periods of time, up to 20 or even 30 years. The comparative analysis reported that there was little or no difference between the breast cancer incidence of the two groups of subjects.

"We found that women who had worked night shifts, including long-term night shifts, were not more likely to develop breast cancer, either in the three new UK studies or when we combined results from all 10 studies that had published relevant data," explained Travis, lead author of the research.

The incidence of developing breast cancer for women who had worked any night shifts was found to be 0.99, while the one for women who worked 20 or more years was 1.01 and the combined relative risks for those who have done night shifts for more than 30 years was 1.00.

Approximately 14 percent of the women in the United Kingdom worked night shifts at least once, while 2 percent have done this for more than two decades. The study was conducted as, in the UK, there are more than 53,000 women annually diagnosed with breast cancer, out of which an average of 11,500 die every year because of the disease.

This problem is especially serious in the UK, where 27,000 women are being denied affordable breast cancer treatment.

Photo: Hernán Piñera | Flickr