Early birds have a lower risk of breast cancer? What you need to know


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Mary Chris Jaklevic is a reporter editor at HealthNewsReview.org. He tweeted as @mcjaklevic.

early bird and breast cancer

Wake me up when it's finished.

There is a lot of misleading information in the news this week about studies of sleep characteristics and breast cancer risk. This is a complicated study to describe, but we get a simple headline like this from HealthDay: "Early Birds Can Have a Lower Risk of Breast Cancer."

The story states: "Compared to night owls, women who wake up early have a 40 percent lower risk of breast cancer, the study found."

Forty percent lower risk? Not too. Despite what readers can collect from this story and others, this research does it not prove that getting up earlier reduces a woman's risk of breast cancer.

In addition, it doesn't even show a connection between getting up early and reducing the risk of breast cancer.

Research doesn't see when women sleep

What HealthDay doesn't explain to readers is that researchers don't really see whether women go up early or go to bed late at night. Instead, they analyzed data from two databases covering around 400,000 women. They examined women's self-reported responses when asked where they fell on the scale between being "morning people" and being "night people" and the genetic variations associated with sleep preferences.

HealthDay also does not provide a real number to show how much the difference "40 percent lower risk" can represent – or how sleep preferences might compare with predetermined breast cancer risk factors. For more information about why it is important to include real numbers, our primary view is about absolute versus relative risk.

The story says "women who sleep longer than the recommended seven to eight hours a night have a 20 percent increased risk of breast cancer for each additional hour of sleep." The data is also problematic because it is based on women's self reporting of how much they sleep. The story does not explain how the data was collected.

For his credit, HealthDay clarified that the study "does not prove a causal relationship between sleep patterns and breast cancer risk" and cites a researcher who said "it is not possible that changing your habits changes the risk of your breasts. cancer."

But the warning appears several paragraphs into the story, where the reader might not pay attention to them. In addition, the story includes other insensitive and seemingly contradictory quotes, such as those referring to the "protective effect" of morning sleep preferences.

CNN warnings that are better explored

Stories about this research were also published on BBC News, CNN, and USA Today. All appear to take their cues from a misleading news release entitled "Women who & # 39; larks have a lower risk of developing breast cancer."

BBC News is the only one of the four that we see that provides absolute data. He wrote that the study "only looked at small portraits, eight years from a woman's life," during that time "that showed two out of 100 owls developed breast cancer compared to one in 100 larks."

CNN does the most complete work to explain the evidence. This is mentioned the warning that is passed by another story:

  • It is not clear whether the findings can be applied throughout the population because the analysis is limited to women of European descent.
  • Sleep habits may not be as significant as existing breast cancer risk factors such as body mass index or alcohol use.
  • There is no known reason why choosing to get up early will prevent breast cancer.

The research method called Mendelian randomization is mentioned in all stories except HealthDays. Only CNN discussed its limitations, citing a researcher who said, "The statistical method used in this study, called Mendel's randomization, does not always allow causality to be concluded."

As the BMJ primer explains, the method "depends on assumptions, and makes sense this assumption must be assessed. In addition, the relevance of the results to clinical decisions must be interpreted with other sources of evidence."

So, although we can hope to hear more about this method because this method is used to study the role of genetic variants in health outcomes, it is still uncertain to tell the public that causation has been undeniably determined.

Unpublished studies that have not been reviewed by colleagues

All stories note that the study was not in a peer-reviewed journal; abstracts presented at medical conferences.

The fact that this research has not been published is one more reason why the data cannot be considered reliable. The validity and importance of unpublished research is often not established, because our headline information about news from scientific meetings explains.

So as far as this report goes, sleep well – whenever you like.


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