Lifestyle Choices Influence Your Breast Cancer Risk
A favorable lifestyle was associated with a reduced risk of breast cancer, according to a study of more than 90,000 women.
Researchers in the United Kingdom, recognizing that almost a quarter of breast cancers are preventable, sought to understand changeable risk factors. What roles are played by lifestyle factors such as:
- oral contraceptives
- hormone replacement therapy (HRT)
Here’s what the investigators did: They reviewed over 90,000 white, post-menopausal women in the United Kingdom Biobank. The study is an ongoing one that looks at the contributions of genetic, environmental, and lifestyle factors in disease. Just over 2,700 women developed breast cancer at a median follow-up of ten years.
To better understand the study, we begin with a review of the researchers’ statistical techniques. If you just rolled your eyes, skip down to the findings section.
“There are three kinds of lies: lies, damned lies, and statistics.” This quote was popularized in the United States by Mark Twain (the pen name of the author and humorist Samuel Langhorne Clemens) and others who mistakenly attributed it to the British prime minister Benjamin Disraeli.
In reality, we do not find the phrase in any of Disraeli’s works, and the earliest known appearances were years after his death. The sentence was attributed to an anonymous writer in mid-1891 and later that year to Sir Charles Dilke. However, others have been reported as the quote’s originators, including many erroneous attributions to Twain himself.
I offer this short diversion as we turn to the statistics the researchers used. Many people have illnesses affected by changes in either one or many of their genes, frequently coupled with environmental factors. Researchers are studying these changes to understand better the role that genetics plays in diseases across different populations.
Polygenic risk score
The site www.genome.gov offers a “polygenic risk score” is one-way people can learn about their risk of getting a disease, based on the total number of changes related to the disease. Here’s how it works:
- Researchers find gene variants linked with complex diseases. They do this by comparing the genomes of individuals with and without those diseases.
- The enormous volume of genomic data allows scientists to learn which variants are more common among those with particular diseases.
- The statistical analysis leads to an estimate of how the collection of a person’s variants affect their risk for a particular disease.
- One can then create a polygenic risk score.
This analysis is done without knowing the specific genes involved in the complex disease. While we may someday know all of the genes involved, researchers can now estimate risk without this full understanding.
The investigators used a polygenic risk score, categorizing subjects as low, intermediate, or high genetic risk. Within each of these risk groups, they then divided the women by the presence or absence of five lifestyle factors linked to a lower risk of breast cancer: Healthy weight, regular exercise, no use of hormone replacement therapy beyond five years, no oral contraceptive use, and alcohol intake of no more than twice per week.
If a woman had four or more of these factors, researchers considered her as having a “favorable lifestyle”; those with two or three factors had an intermediate lifestyle; those with fewer factors had an unfavorable lifestyle.
The data revealed an association between breast cancer and the following lifestyle characteristics:
- body mass index (BMI) 25 or higher (risk increased by 1.14-times)
- no regular physical activity (risk increased by 1.12-times)
- alcohol at least thrice weekly (risk increased by 1.11-times)
- history of oral contraceptive use (risk did not change)
It gets more interesting when we look at genetic risk groups. For those in the low genetic risk group, an intermediate lifestyle raised the risk by 1.4-times, an unfavorable lifestyle by just over 1.6-times. In the intermediate-risk group, middle and adverse lifestyles lifted breast cancer risk by 1.4- and 1.9-times, respectively (compared with a favorable lifestyle).
Even in the high genetic risk group, lifestyle appears to matter. Those with intermediate lifestyles had a 1.13-times increase in the risk of developing breast cancer. Those with an unfavorable lifestyle raised their chances by a factor of 1.4. Researchers adjusted these results for both age and family history.
The results suggest that healthy lifestyles through adequate exercise, a healthy weight, no or limited alcohol intake, and no hormonal replacement therapy should be encouraged to reduce breast cancer risk.
The research authors offer that “following a healthy lifestyle appears to be associated with a reduced level of breast cancer risk in all three genetic risk strata, showing a role of lifestyle for common diseases with a genetic predisposition, such as breast cancer.”
And now the caveats:
- The study needs replication.
- Unfortunately, the research did not include non-white, non-postmenopausal women.
- Researchers did not differentiate between breast cancer subtypes.
- Oral contraceptives did not appear associated with increased breast cancer risk, but historical studies have shown a link.
These lifestyle changes promote overall health, including reducing cardiovascular disease (the greatest threat to a woman’s life in many countries).
I’m Dr. Michael Hunter.
“Have Your Say.” Winnipeg Free Press, F.P. Canadian Newspapers Limited Partnership, 27 Nov. 2015, p. n/a.