Sleep traits could be a risk factor for breast cancer, new research suggests. Women who said they preferred to get out of bed early were found to have a lower risk of breast cancer than those who stay up late.

Axar.az reports citing CNN.

However, experts cautioned that other breast cancer risk factors such as alcohol consumption and being overweight have a greater impact than sleep and said there was no reason to change your sleep patterns.

One out of 100 women who considered themselves morning people developed breast cancer, compared with two in 100 women who described themselves as evening people, according to the study, which was published Wednesday in the BMJ.

The study also found that sleeping more than the average seven to eight hours per night was found to have a slightly increased risk of breast cancer. It also found there was little link with insomnia.

Researchers used information from more than 400,000 women in two large data banks -- around 180,000 women from UK Biobank study and more than 220,000 women from the Breast Cancer Association Consortium study. Participants' preference for waking early or late was included in the data.

According to 2016 figures from the charity Cancer Research UK, breast cancer is the most common type of cancer in the UK. In the US, the American Cancer Society estimates that more than 260,000 cases of invasive breast cancer will be diagnosed in women in 2019.

"The main lifestyle risk factors that we know are clearly associated with breast cancer are alcohol intake and obesity or high Body Mass Index," said Relton.

"Sleep is likely to be an important risk factor for breast cancer, but it isn't as large as other well-established risk factors like BMI or alcohol," said lead author Dr. Rebecca Richmond, last year. Richmond is currently a research fellow at the MRC Integrative Epidemiology Unit at the University of Bristol.

Schernhammer cited observational studies that suggested that unlike night owls, early risers that work night shifts have an increased risk of type 2 diabetes. This provided "additional support for the biological importance of circadian misalignment," she said.