Maintaining a healthy body weight, being physically active, and following a healthy dietary pattern can help women live longer after breast cancer diagnosis, according to a major new analysis of the latest research.
Breast cancer is the most commonly occurring cancer in women around the world, with roughly 2.3 million cases and 700,000 deaths in 2020 alone. Currently, there are about 7.8 million women worldwide living at least 5 years beyond their diagnosis.
“Many women living with breast cancer seek lifestyle advice. It is important that they have access to reliable information about healthy living,” commented the co-author of the review, Doris Chan, PhD, from the School of Public Health at Imperial College London in London, England.
“The findings from these reviews strengthen the case for women with breast cancer to be supported by their healthcare team to make positive behavior changes. These could include eating a healthier diet and being physically active, all of which play a role in maintaining a healthy weight,” Chan said in a statement.
The new review — part of the World Cancer Research Fund International Global Cancer Update Programme — was published online October 24 in four papers in the International Journal of Cancer. October is breast cancer awareness month.
Maintain Normal Body Weight
After menopause, being overweight or gaining weight are established risk factors for developing breast cancer, yet the impact of excess body weight on the course of breast cancer is less clear.
To investigate, Chan and colleagues reviewed 226 studies with more than 456,000 women with breast cancer.
They found “strong” evidence (likelihood of causality: probable) that higher BMI after diagnosis is associated with increased all-cause mortality (64 studies, 32,507 deaths), breast cancer-specific mortality (39 studies, 14,106 deaths), and second primary breast cancer (11 studies, 5248 events).
The respective summary relative risks (RR) per 5 kg/m2 BMI were 1.07 (95% CI, 1.05 to 1.10), 1.10 (95% CI, 1.06 to 1.14), and 1.14 (95% CI, 1.04 to 1.26), with high between-study heterogeneity but generally consistent positive associations.
The review also found “limited-suggestive” evidence that higher post-diagnosis BMI is associated with higher risk for breast cancer recurrence, nonbreast cancer-related mortality, and cardiovascular mortality.
One randomized controlled trial shows the potential beneficial effects of intentional weight loss on disease-free survival, but the reviewers say more intervention trials and well-designed observational trials in diverse populations are needed to draw firm conclusions.
Physical Activity
To clarify the impact of physical activity on breast cancer prognosis, the reviewers looked at 23 observational studies with more than 39,000 women with breast cancer. Most of the studies looked at recreational physical activity, such as aerobics, walking, and running, with limited studies on other types of activity.
In linear dose-response meta-analysis, each 10-unit increase in metabolic equivalent of task hours per week (MET-h/week) of higher recreational physical activity was associated with 15% and 14% lower risk of all-cause and breast cancer-specific mortality, respectively, they report.
Recreational physical activity was not associated with breast cancer recurrence.
Nonlinear dose-response meta-analyses indicated 48% lower all-cause and 38% lower breast cancer-specific mortality with increasing recreational physical activity up to 20 MET-h/week, but little further reduction in risk at higher levels.
Predefined subgroup analyses across various factors including BMI, adjustment for confounders, and physical activity intensity were consistent in direction and magnitude to the main findings.
However, considering the methodological limitations of the included studies, an independent expert panel concluded that there is “limited but suggestive” data that recreational physical activity is beneficial in lowering risk of all-cause and breast cancer-specific mortality, the authors report.
Overall, the findings “support the development of lifestyle recommendations for breast cancer survivors to avoid obesity and be physically active, within the limits of their ability and specific medical advice,” the authors conclude.
Jury Out on Dietary Factors?
To assess the impact of dietary factors after breast cancer, the researchers evaluated 108 studies with more than 151,000 women.
Meta-analysis for dietary patterns, vegetables, whole-grains, fish, meat and supplements was not possible due to few studies, often with insufficient data, they note.
Meta-analysis was only possible for all-cause mortality with dairy, isoflavone, carbohydrate, dietary fiber, alcohol intake, and serum 25-hydroxyvitamin D (25(OH)D), and for breast cancer-specific mortality with fruit, dairy, carbohydrate, protein, dietary fat, fiber, alcohol intake, and serum 25(OH)D.
“The results, with few exceptions, were generally null,” the reviewers report.
However, they did find “limited-suggestive” evidence that predefined dietary patterns may reduce the risk of all-cause and other causes of death, as follows:
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Isoflavone intake reduces the risk of all-cause mortality (RR, 0.96 per 2 mg/d), breast cancer-specific mortality (RR, 0.83 for high vs low), and recurrence (RR 0.75 for high vs low).
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Dietary fiber intake decreases all-cause mortality (RR, 0.87 per 10 g/day).
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Serum 25(OH)D is inversely associated with all-cause and breast cancer-specific mortality (RR, 0.93 and 0.97 per 10 nmol/L, respectively).
The remaining associations were graded as “limited-no conclusion.”
The reviewers say “stronger evidence, contributed by intervention trials and/or well-conducted observational studies, is needed before specific dietary recommendations for improving breast cancer prognosis can be made.”
Currently, there are no evidence-based nutritional guidelines specifically developed for breast cancer survivors.
Co-author Helen Croker, PhD, with the World Cancer Research Fund International, said the group hopes to develop recommendations specifically for people living with and beyond cancer.
“Analyzing and interpreting the existing literature is the first step towards these efforts,” she said.
Funding was provided by the World Cancer Research Fund network of charities (American Institute for Cancer Research; World Cancer Research Fund). The authors have disclosed no relevant financial relationships.
Int J Cancer. Published online October 24, 2022. Full text: Study 1, Study 2, Study 3, Study 3
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