Research published in the British Medical Journal (BMJ) has found links between sleep habits and cáncer risk. The study found that being a morning person (someone who prefers getting up earlier in the morning) reduced your risk of developing cáncer de mama. Evening people and those sleeping for longer than the recommended seven to eight hours a night were shown to have a heightened risk of breast cancer.

The international research team used a technique called Mendelian randomisation for over 300 thousand women in the UK Biobank study and the Breast Cancer Association Consortium (BCAC) study. They analysed genetic information associated with three sleep traits: morning or evening preference, sleep duration and insomnio. Morning preference was associated with a slightly reduced risk of breast cancer - one less woman in 100 compared to evening preference.

One in eight women in the UK will develop breast cancer at some point in their lives according to Cancer Research UK. Most cases occur in women over 50 but much younger women can have breast cancer. It is now the most common cancer in the UK with around 48,000 cases a year.

Previous studies have shown a link between night shift work and an increased risk of breast cancer, thought to be attributed to light exposure at night, disrupted sleep patterns and lifestyle factors. This study highlights that this risk is also heightened for those who go to bed and wake later. However, the authors stress that the extent of the effect is likely smaller than other risk factors like IMC and alcohol intake.

The researchers say that their findings "have potential implications for influencing sleep habits of the general population in order to improve health".

Weilin Wu, Health Information Officer at Cancer Research UK, said: "Initial results from this large study found that women whose genes predisposed them to be early risers could have a reduced risk of breast cancer. But the next important step to understand how sleep may affect cancer risk would be to look at people's actual sleep pattern and the other factors that might be playing a role in when people get up in the morning."

In a linked editorial, Professor Eva Schernhammer from the University of Vienna argues that the study offers an opportunity to amend working hours, particularly for shift workers, in order to protect health and use a personalised approach to reduce the risk of chronic diseases linked with the circadian system. She recognises that the results "identify a need for future research exploring how the stresses on our biological clock can be reduced".

This study was published in the British Medical Journal (BMJ).