Being a day person (popularly known as larks) is associated with a lower risk of developing breast cancer, as opposed to being a nocturnal person (known as owls), according to the findings of a study published in the journal 'The BMJ', which suggests that sleeping longer than the recommended 7-8 hours per night can also carry a greater risk.
Previous studies have shown a relationship between night work and the risk of breast cancer, which is thought to be due to interrupted sleep patterns, exposure to light at night and other lifestyle factors. But there has been much less research on the potential effects of sleep habits on the risk of breast cancer.
Then, an international research team set out to examine whether certain features of sleep could have a direct (causal) effect on the risk of developing breast cancer.
Using a technique called Mendelian randomization, they analyzed the genetic variants associated with three particular features of sleep (morning or night preference (chronotype), sleep duration and insomnia) for 180,216 women in the Biobank study in the United Kingdom and 228,951 women in the Consortium. of the Breast Cancer Association (BCAC Study).
The analysis of genetic information in this way avoids some of the problems that affect traditional observation studies, which makes the results less prone to unmeasured (confusing) and, therefore, more reliable factors.
In the observational analysis of data from the UK Biobank, morning preference was associated with a slightly lower risk of breast cancer (one woman less per 100) than night preference, while there was little evidence of an association with duration of sleep and the symptoms of insomnia.
However, the authors emphasize that this represents differences at the extremes of the scale and that the scope of the effect is likely to be less than that of other known risk factors for breast cancer, such as BMI and alcohol consumption.
Mendelian analysis of data from the UK Biobank provided some supporting evidence for a protective effect of morning preference on breast cancer risk, but with imprecise estimates for sleep duration and insomnia symptoms.
The Mendelian analysis of BCAC also supported a protective effect of morning preference and showed a potential harmful effect due to a longer duration of sleep (more than the recommended 7-8 hours) in breast cancer, while the evidence of symptoms of Insomnia was inconsistent.
The researchers believe that their findings “provide strong evidence for a causal effect of the chronotype on the risk of breast cancer.” They add that more work is needed to discover the possible reasons for the associations between sleep interruption and breast cancer. However, these findings “have potential implications for influencing the sleep habits of the general population to improve health”.
In a linked editorial, Professor Eva Schernhammer, from the University of Vienna, agrees that these findings “identify the need for future research that explores how tensions can be reduced in our biological clock”.