Changes in lifestyle reduce breast cancer risk, model showsBMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d4041 (Published 27 June 2011) Cite this as: BMJ 2011;342:d4041
Changes in alcohol consumption, physical activity, and body mass index (BMI) reduce the absolute risk of breast cancer by a small but significant amount, a new modelling study has shown.
To estimate the risk of breast cancer the researchers used data from a case-control study of women in Italy (2569 cases and 2588 controls) conducted from 1991 to 1994, together with incidence and mortality data from registries.
They then used these figures to develop a model to predict the absolute risk of breast cancer on the basis of three modifiable risk factors: alcohol consumption, leisure time physical activity, and body mass index. They also included five non-modifiable risk factors: reproductive characteristics, education, occupation, family history, and biopsy history.
Their results showed that the lowest risk lifestyle profile—never drinking alcohol, exercising for at least two hours a week, and maintaining a BMI of <25 after the age of 50—was associated with a 1.6% reduction in average 20 year risk of breast cancer in women aged ≥65 years (Journal of the National Cancer Institute doi:10.1093/jnci/djr172).
Although apparently small, this risk reduction translates to 16 000 fewer cases of breast cancer in a general population of one million women.
The researchers, led by Elisabetta Petracci, from the US National Cancer Institute, say, “These data give perspective on the potential reductions in absolute breast cancer risk from preventative strategies based on lifestyle changes.” They suggest that their methods may be useful for designing studies to investigate the effect of breast cancer prevention programmes.
The model showed greater risk reductions in women at a higher risk of developing breast cancer. The average reduction in average 20 year breast cancer risk was 3.2% in women with a positive family history of breast cancer and 4.1% in those with the most non-modifiable risk factors.
Although these risk reductions are greater than in the general population, encouraging adoption of low risk lifestyle factors by the 8% of postmenopausal women with a positive family history of breast cancer would prevent only 2560 breast cancers in a population of one million women.
This illustrates that “broadly applicable interventions can be more effective than interventions on high-risk subgroups,” the researchers write.
In an accompanying editorial, Kathy Helzlsouer, from the Mercy Medical Center in Baltimore, considers that the study “provides extremely important information relevant to counseling women on how much risk reduction they can expect by changing behaviors” (doi:10.1093/jnci/djr222).
She adds, “It also highlights the basic public health concept that small changes in individual risk can translate into a meaningful reduction in disease in a large population.”
Dr Helzsouer says that calculation of absolute risk reduction is a major strength of the study. However, she argues that the estimates are based on optimistic assumptions about changing behaviour. And the findings don’t necessarily apply to women in other countries, such as the US, where breast cancer rates among older women are much higher than in Italy.
“These differences, however, serve to emphasise the need for models such as these to be created on the basis of local data to provide the best estimates of risk to aid decision making, whether for the individual or the population in public health settings,” she concludes. She suggests that studies should now be carried out to verify that changing health related lifestyle behaviours leads to a change in breast cancer risk.
Stephen Duffy, Cancer Research UK’s professor of cancer screening, said, “The risk model used in this study appears to be a reasonable one, in that it has comparable accuracy to other commonly used breast cancer risk models. A key finding is that there are worthwhile ways potentially to reduce breast cancer risk by adopting a more active lifestyle and losing excess weight. But it is important to note that modifications in risk cannot always be achieved on an individual basis. For example, someone who gives up drinking becomes an ex-drinker, but they cannot be classified as someone who has never been a drinker.
“The big question is how much of this potential risk reduction is actually achieved by changes in lifestyle. For example, if a person has been overweight for 20 years, to what extent does a sudden weight loss change the absolute risk? Although we don’t know for sure, results of other studies suggest that such changes do bring about a reduction in future incidence of breast cancer.”
Cite this as: BMJ 2011;342:d4041