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If you’re a woman who greets the early morning with a smile, new research delivers good news, you have a slightly reduced risk of developing breast cancer.

Being a morning person was associated with a slightly lower risk of breast cancer. Other studies find early risers are healthier and wealthier.

New large-scale research has found that women who are naturally morning people may have a lower risk of breast cancer than those who are night owls.

Carried out by UK, US, French, and Norwegian researchers, the new study looked at or 180,216 women taking part in the UK Biobank study, a large long-term study which includes genomic data on more than half a million UK residents, and 228,951 women in the Breast Cancer Association Consortium (BCAC) study.

The researchers describe their methods and findings in a recent BMJ paper.

For their analysis, they used data on 180,216 women from the UK Biobank and 228,951 women from the Breast Cancer Association Consortium.

They report that they found ‘consistent evidence’ of morning preference having a ‘protective effect’ on breast cancer risk.

They also found ‘suggestive evidence’ that sleeping more than 7–8 hours per night could have an ‘adverse effect’ on breast cancer risk.

The researchers emphasise that the effects they found are small, compared with that of other risk factors for breast cancer, such as BMI, alcohol consumption, and smoking.

Focus on traits rather than modifiable factors

The researchers wanted to carry out the study because a lot of published research on breast cancer risk and sleep has tended to focus on ‘night shift work and exposure to light at night.’

Far fewer studies have focused on traits or personal attributes that individuals find much harder to change, if they can change them at all. A preference for morning or evening is an example of such a trait, which the authors describe as a ‘chronotype.’

They note that a number of ‘large genome-wide association studies’ have generated robust genetic profiles for chronotype (i.e., morning or evening preference), sleep duration, and symptoms of insomnia.

In the new study, the researchers carried out two types of analysis. In the first type, they ran a multivariable regression analysis on the UK Biobank data to find links between breast cancer and what each participant reported as their morning or evening preference, sleep duration, and insomnia symptoms.

In the second type of analysis, they used participants’ genetic profiles of chronotype, sleep duration, and insomnia to look for links between these and breast cancer.

This second type of analysis is called Mendelian randomisation (MR), and they ran this on the UK Biobank data and also two samples of Breast Cancer Association Consortium (BCAC) data.

The team compiled the genetic profiles from “341 single nucleotide polymorphisms (SNPs) associated with chronotype, 91 SNPs associated with sleep duration, and 57 SNPs associated with insomnia symptoms.”

Morning preference tied to lower risk

The multivariable regression analysis of the UK Biobank data showed that women with a morning preference had a less than 1% lower risk of breast cancer, compared with women with an evening preference.

A factor that has a less than 1% effect on women’s breast cancer risk means that it affects fewer than 10 women in 1,000.

This first analysis found “little evidence for an association between sleep duration and insomnia symptoms.”

The MR analysis of the UK Biobank data supported these findings, as did the MR analysis on two samples of BCAC data, with one exception. This showed a small “adverse effect of increased sleep duration on breast cancer risk.”

The team chose to use MR analysis because their data came from observational studies, which are studies that track people over time. Such studies can only find links between variables; they are not able to prove that one variable actually causes another.

By using MR analysis and other methods, and ruling out known risk factors, the researchers sought to make their results more reliable and less disrupted by factors that they could not measure.

In other words, they took observational data as far as they could toward supporting that a cause-and-effect link exists, although that type of data does not comprise proof.

The findings, published by The BMJ Thursday, showed consistent evidence that being a morning person was associated with a lower risk of developing breast cancer than being an evening person.

There was also suggestive evidence that sleeping longer than the recommended 7 to 8 hours a night was associated with an increased risk of the disease, although the findings were unclear for what effect insomnia may have on breast cancer risk.

The team added that the effects of sleep habits are likely to be smaller than the effects of other known risk factors for breast cancer, such as Body Mass Index (BMI) and alcohol intake, although they add that the findings do have implications for influencing sleep habits to improve health.

Women who do night shift work have also been found to have an increased risk of breast cancer, possibly due to this type of work disrupting sleep patterns and exposing women to light during the night-time.

Source: Medical News Today

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