Wednesday February 22 2017
Exercise may reduce inflammation of breast tissue
"A half hour stroll a day can help women who've survived breast cancer prevent the killer disease returning," The Sun reports.
A review of recent evidence, carried out by Canadian researchers, was prompted by the fact that many women who undergo treatment for breast cancer are eager to make lifestyle changes that may help reduce the risk of the cancer returning. But there is a great deal of often conflicting advice, so it is hard to make an informed decision.
The researchers' review of evidence found that physical activity had the strongest reported effect on reducing the risk of breast cancer recurring and dying from breast cancer.
Following the recommended 150 minutes of moderate to vigorous exercise or 75 minutes of vigorous exercise per week guidance, as well as two to three weekly sessions of strength training, can help reduce the risk of breast cancer returning and death from the disease.
The effects of treatments such as surgery and chemotherapy can take a toll on motivation to exercise. But clinical guidelines recommend a gradual return to regular exercise.
Where did the story come from?
The study was carried out by researchers from the Division of medical Oncology and Hematology, Odette Cancer Centre Sunnybrook Health Sciences Centre, Toronto, Canada.
The researchers did not report any funding for the study and declared no competing interests.
The study was published in the peer-reviewed Canadian Medical Association Journal and is open-access meaning it is free to read online.
The Mail Online and The Sun reported the story very similarly, emphasising the importance of exercise in reducing risk of relapse.
Interestingly, the headline of The Sun was very positive, "brisk 30-minute walk a day 'STOPS killer breast cancer returning'," whereas the Mail Online took a much more pessimistic stance, "boozing, weight gain and failing to exercise INCREASES the risk of breast cancer returning".
It should be pointed out that The Sun's headline is not entirely accurate as we only know that exercise reduces the risk and doesn't actually stop it.
The Sun also quotes one of the authors of the study, Dr. Ellen Warner, who cautions that "some breast cancers have aggressive biology and will recur despite the most meticulous lifestyle behavior … Patients should not be made to feel that inadequate lifestyle changes have led to recurrence of their cancer."
What kind of research was this?
This was a review of systematic reviews (and related meta-analyses) and primary research, that aimed to summarise the role of lifestyle factors in the prognosis of women who have had breast cancer.
It aimed to identify which lifestyle changes can be recommended to women in addition to breast cancer treatments, to reduce their risk of future recurrence and death.
This type of review is a good way of summarising research in an area, however findings can only be as reliable as the studies included.
There were a variety of study types included, but most were systematic reviews of individual observational studies, so they were unable to account for all confounding factors and therefore reliability might be variable.
In addition, we don't know whether all relevant studies have been included. This means there is potential for selection bias.
What evidence on physical activity did they find?
- A meta-analysis of 22 cohort studies found that physical activity can reduce the risk of deaths caused by breast cancer by around 40% (hazard ratio [HR] 0.59, 95% confidence interval [CI] 0.45 to 0.78). This is the biggest effect of any lifestyle factor on breast cancer outcomes.
- At least 150 minutes per week of physical activity is recommended.
What evidence on weight management did they find?
- Weight gain of more than 10% of baseline body weight during or after breast cancer treatment may reduce survival, but the evidence is weak and the result could be due to chance HR 1.17, 95% CI 1.00 to 1.38).
- Weight gain of less than 10% is not associated with reduced survival.
- Risk of recurrence of breast cancer may be increased by weight gain, but this is just based on observational studies. Therefore, many other factors could be responsible.
- Women who are obese or overweight at breast cancer diagnosis have poorer outcomes.
- It remains unknown whether weight loss has a preventive effect.
What evidence on diet did they find?
- They did not find robust evidence on any diet and risk of recurrence or mortality.
- Observational studies have not shown any difference between Western-style diets (high in processed grains, processed meats and red meat) and diets high in fruits, vegetables, whole grains and chicken on the rate of breast cancer recurrence.
- Soy products were not found to increase breast cancer recurrence. There have been claims that, as soy contains phyto-oestrogens (which are similar to the hormone oestrogen), they could stimulate abnormal cell growth. The review actually found soy may reduce cancer risk, although evidence for this is weak.
What evidence on smoking did they find?
- Based on a large observational study of 20,691 women, those who continue to smoke after a breast cancer diagnosis are 72% more likely to die from breast cancer than women who have never smoked (HR 1.72, 95% CI 1.13 to 2.60).
- There is insufficient evidence on whether quitting smoking after diagnosis has an effect on breast cancer-specific survival, but it will reduce the risk of other cancers, such as lung cancer, and cardiovascular disease such as heart attack and stroke.
What evidence on alcohol intake did they find?
- They could not say whether alcohol consumption affects breast cancer outcomes or not.
- However, reducing alcohol consumption to one or fewer drinks per day reduces the risk of a new (not recurring) breast cancer.
What evidence on vitamin supplementation did they find?
- Moderate increases in dietary vitamin C or oral supplementation may reduce breast cancer mortality. Randomised controlled trials are needed to confirm this.
- Most patients would benefit from vitamin D supplementation, at least to optimise bone health.
This was a helpful summary of recent research into how lifestyle changes impact on the risk of breast cancer returning, but it does have some limitations.
Researching lifestyle factors separately is always difficult as they tend to clump together, making it difficult to pick apart individual factors. For example, people who are more physically active tend to have a healthier diet and are less likely to drink excessive amounts of alcohol or smoke.
While the researchers say many studies attempt to make adjustments for these confounding factors, it is difficult to know which studies did this and how successful they were. It is also possible that women who did not exercise were unable to because of adverse effects from their breast cancer treatment.
There is also the fact that lifestyle factors were only looked at after breast cancer diagnosis, when lifestyle before diagnosis might have long term effects.
Still, the conclusion that regular exercise appears to be the best option seems reasonable and appropriate. Aside from cancer prevention, regular exercise can also help reduce the risk of other chronic diseases, such as heart disease.
Read more about the benefits of exercise.