The Role of Physical Activity and Exercise in Breast Cancer Prevention
Breast Cancer and Prevention
Breast cancer is one of the most common cancers worldwide*, it is also the second leading cause of cancer death in women, with one-in-eight women developing breast cancer at some point in their lifetime. 
Initially thought to be a hereditary disease, only about 5% to 10% of cancers are based on inherited genes , and the figure is even lower for breast cancer as only 3% of patients with the disease inherited it.  The 3% refers to breast cancers caused by single inherited genes mutations such as a faulty BRCA1 gene. But even having a positive predictive genetic test for cancer risk genes doesn't mean you have cancer or are going to develop it.
What are some of the main risk factors involved in Breast Cancer?
There are certain risks involved in breast cancer which we have little control over. For example, two of the main risk factors for developing breast cancer, are:
Being a woman - over 99% of new cases of breast cancer are in women.
Ageing - more than 80% of breast cancers occur in women over the age of 50. Most men who get breast cancer are over 60.
There are other factors that you may have some control over, for example lifestyle choices could drastically impact the chances of developing breast cancer. Concerning research studies, these comprise but are not limited to:
overweight and obesity 
alcohol consumption  
hormone replacement therapy  
Physical Activity Could Reduce Lifetime Risk by Up to 25%
Over the past two decades, there has been significant research into the impact exercise, and physical activity has on breast cancer. The evidence is pretty much incontrovertible: regular exercise can reduce your risk of breast cancer. The only question to ponder, is by just how much?
Based on a systematic review in 2007 of 19 cohort studies and 29 case-control studies, there was strong evidence for physical activity’s impact on post-menopausal breast cancer with risk reductions ranging from 20% to 80%. Confirmed in multiple demographic and population groups. 
A meta-study carried out in 2014 which reviewed 73 individual studies revealed that women could significantly reduce the risk of obtaining breast cancer by an average of 25% if they exercise regularly compared with inactive women. The association was most evident in post-menopausal women who performed moderate-to-vigorous exercises regularly sustained over a lifetime and vigorous-intensity activity lowering the risk of pre-menopausal breast cancer .
The National Cancer Institute, based in the United States, also conducted a comprehensive review of thirty-one different studies which revealed that the average breast cancer risk reduction rate is 12%. The figure is the same for both pre- and post-menopausal women .
Also, women after menopause who tend to be more physically active have a lower risk of breast cancer than women who are inactive. .
Finally, the Susan G. Komen Foundation, a leading organisation in the fight against breast cancer, reports that exercising regularly can reduce the risk of breast cancer by anywhere from 10 – 20% based on a research review .
Thus, if you take the above physical activity studies into account, one's lifetime breast cancer risk could be reduced markedly.
How can physical activity help prevent breast cancer?
While medical researchers are pretty much agreed that physical activity helps to prevent breast cancer, less is known about the mechanisms that make it possible. One prevailing theory is that physical activity helps to lower the level of circulating hormones (principally oestrogen, leptin and insulin) and related growth factors such as IGF-1, and reduces levels of chronic inflammation markers in the body for instance, C-reactive protein, which can contribute to cancer development and progression. It also enhances the immune system and decreases oxidative stress. 
Some say physical exercise has an indirect effect, as it helps to reduce overweight and obesity. By helping you to manage your weight, especially around the waist, physical activity plays a significant role in lowering the risk factors linked to risk of chronic diseases and cancer.  However, more importantly, the physical activity itself has a protective effect, which is independent of its impact on body weight, in other words, it is beneficial even if you are not losing weight.
Also, there are other ways that physical activity can be used to reduce your risk of breast cancer. The National Cancer Institute (NCI) states that exercise is also very good at bolstering your immune system. The stronger your immune system, the more potent it is when it comes to tackling cancer cells. The NCI also notes that physical activity might lessen your exposure to cancer-causing agents (carcinogens) by reducing the time it takes food to travel through your digestive tract. 
How much physical activity do you need?
Advice from the Chief Medical Office (CMO) in the UK recommends a minimum of 150 minutes per week of moderate-intensity physical activity. You can exercise for less time, 75 minutes per week, if the intensity is vigorous. It also recommends at least 2 days of strength or resistance training too.  Cancer Research UK, backs this up and uses the 150 minutes figure as an important baseline.
However, there is evidence that more is better - with a 6% decrease in relative risk for each for each additional hour of physical activity per week. The greatest reduction is risk found with exercise during reproductive years with at least 5 hours of strenuous activity per week. 
What Types of Physical Activity?
Examples of moderate-intensity physical activity would be a brisk walk, light gardening or ballroom dancing.
Is Exercise All I Need To Focus On?
Exercise, while a powerful tool, is not going to be enough to prevent breast cancer entirely. It is just one pillar of a healthy lifestyle that can reduce your risk of chronic disease.
Seek Out Joy in Movement
We all knew exercise was beneficial for breast cancer prevention now we know some of the reasons why. It helps us feel good too.
*Lung and breast cancers are the most common cancers worldwide, each contributing 12.3% of the total number of new cases diagnosed in 2018. (wcrf.org)
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