How Does Exercise Reduce Breast Cancer Risk?
Regular exercising comes with a range of health benefits, one of which is reduced risk for developing breast cancer. Many studies conducted over the last 20 years have consistently reported a lower risk of breast cancer among women engaging in regular physical activity.
However, the exact mechanism behind this is unclear. Being active may lower estrogen levels in the body. Studies have shown that women with lower blood estrogen levels have a lower risk of breast cancer than women with higher levels.
Adipose tissue is the primary source of estrogen in postmenopausal women. So, reducing body fat with exercise can lower estrogen production and significantly reduce breast cancer risk in postmenopausal women.Â
In addition, exercise also reduces inflammation in the body, strengthens the immune system, decreases insulin resistance, and reduces oxidative stress – all of which are risk factors for breast cancer development.
Exercises and Breast Cancer Risk – What Do The Studies Say?
A study published in The Journal of the American Medical Association in 2005 reported that physical activity after breast cancer diagnosis might reduce the risk of death due to the disease.
Women who performed physical activity equivalent to walking for 3 to 5 hours per week at an average pace benefited the most.
The study also reported that physical activity after breast cancer diagnosis reduced the chances of recurrence and improved the quality of life in these women.
The primary reason cited for the reduced risk is the low levels of circulating estrogen.
A study conducted in 2015 reported that weight loss by exercise resulted in an increase in lean mass, greater fitness, and a positive effect on the serum sex hormone levels due to greater loss of body fat.
These effects have been associated with a decreased risk of postmenopausal breast cancer.
A systematic review analysis was conducted and published in 2019, wherein researchers studied 38 cohort studies published between 1994 and 2017 comprising 68,416 breast cancer cases.
The researchers observed that the risk for breast cancer was significantly lower in people with exposure to physical activity longer than a year but less than five years, followed by those who had a lifetime exposure to physical activity.
In a study published in 2014, the authors found that breast cancer and colorectal cancer survivors, who increased their physical activity before or after their cancer diagnosis, showed a decreased mortality risk compared with those who were inactive or did not change their physical activity levels.
How Does Genetics Influence Exercise And Breast Cancer Risk?
The MTRR Gene
5-methyltetrahydrofolate-homocysteine methyltransferase reductase or MTRR gene gives instructions for producing the enzyme methionine synthase reductase, which is required for the normal functioning of enzyme methionine synthase.Â
Certain changes in the MTRR gene can induce insulin resistance, thereby making the cells unresponsive to insulin. This can result in type 2 diabetes.Â
Previous studies reported the association of this genetic change with lung and colorectal cancers, but not with breast cancer.
A 2019 study examined the effect of genetically driven insulin resistance on breast cancer risk.
The researchers identified a Single Nucleotide Polymorphism (SNP) rs13188458 in the MTRR gene. It was found that, in a group of physically inactive people, those with the T allele of this SNP had a greater risk for abnormally high insulin levels (hyperinsulinemia) and breast cancer than people with the G allele.
| Allele | Implication |
| T | Higher risk for hyperinsulinemia and breast cancer when physically inactive |
| G | Normal risk for hyperinsulinemia and breast cancer when physically inactive |
The ERCC4 Gene
ERCC Excision Repair 4, Endonuclease Catalytic Subunit or ERCC4 plays an essential role in repairing damaged DNA. A defect in this gene has been associated with Xeroderma pigmentosa, a skin condition.
A meta-analysis done in 2011 revealed an association between ERCC4 and breast cancer risk. rs1800067 is an SNP in the ERCC4 gene.
Postmenopausal women with the GG genotype of this SNP who engaged in >9.23 hours of recreational physical activity per week experienced statistically significant reductions in breast cancer risk.
| Genotype | Implication |
| GG | Significant reduction in breast cancer risk with exercise |
| AG | Modest reduction in breast cancer risk with exercise |
| AA | Normal risk of breast cancer with exercise |
The MLH1 Gene
The MLH1 or MutL homolog 1 gene is a part of MMR or mismatch repair set of genes. It repairs damaged DNA by replacing the portion containing the errors with the corrected sequence.
rs1799977 is an SNP in the MLH1 gene. Women with the G allele of this SNP who were active during the postmenopausal years experienced significant breast cancer risk reductions.
| Allele | Implication |
| G | Significant reduction in breast cancer risk with physical activity in postmenopausal women |
| A | Normal breast cancer risk with physical activity in postmenopausal women |
How To Reduce Your Risk of Breast Cancer with Exercise
Researchers have observed that postmenopausal women who exercise for at least 300 minutes per week can successfully reduce their body fat compared to those who spent half that time.
Even 2.5 hours of brisk walking per week can reduce breast cancer by as much as 18%!
If you are in a dilemma about how to begin your exercise, here are some handy and effective tips to help you exercise the right way to keep breast cancer at bay:
- Focus on building an exercise routine. It is okay to begin slowly, but consistency is vital.
- Aerobic exercises like walking, running, cycling, swimming, dancing, etc., are highly beneficial for weight loss, reducing cholesterol levels, increasing endurance and stamina, relieving stress, and ensuring you get good sleep. All of these can help reduce breast cancer risk.
- Wear a pedometer during the day to keep track of your daily step count and aim to increase the steps every day.
- Skip the elevator and take the stairs whenever you can.
- Avoid taking a vehicle if your destination or workplace is nearby. Walking or cycling may be a better option.
- Love watching TV? Use a stationary bike or treadmill to keep the calories burning while you binge-watch your favorite show.
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Summary
- Studies have consistently reported lower breast cancer risk among women who exercise regularly.
- Exercising reduces the estrogen levels in the body, thereby reducing your breast cancer risk.
- Several studies report a positive effect of exercising, not only on breast cancer risk but also on breast cancer prognosis and survival.
- People with a certain genetic type tend to benefit more in terms of breast cancer risk reduction with exercises.
- Brisk walking for even 2.5 hours per week could bring down breast cancer risk by 18%!
- Aerobic exercises like jogging, cycling, and swimming also seem to be effective in reducing breast cancer risk.
