Cancer And Physical Activity

What is cancer?

Cancer is one of the leading causes of death globally. According to the World Health Organisation (WHO), cancer is a group of diseases caused by abnormal cells which grow and divide uncontrollably, thus invading the spaces in surrounding tissues and spreads to other organs in a process called metastasis. 

Mutations in DNA sequences cause uncontrollable cell division. Some of the main risk factors for cancers include exposure to radiation, chemicals, viruses, family history, and lifestyle factors. 

The most common cancers that are threatening the global population are breast, lung, colorectal, prostate, and skin cancers.

Regular physical activity lowers the risk of cancer 

There were suggestions that regular exercise may lower the number of cancer cases by 40%, and this effect is most evident in breast and colorectal cancers.¹

Preventing obesity

Obesity is a chronic disease that has been suggested to increase the risk of many cancers, including colon, breast, liver, and kidney cancers.² The World Health Organisation (WHO) defines obesity as having a body mass index (BMI) >30. 

Adipocytes, also known as fat cells, are cells that not only store fats, but also produce proteins important for regulating metabolism in the body. The two main hormones that adipocytes produce are leptin and adiponectin. The hormone leptin regulates our food intake by decreasing our appetite, while the hormone adiponectin helps to regulate our glucose level by promoting insulin sensitivity in the muscles and liver.

When a person is obese, they have more adipocytes of a larger size, and the number of hormones they also release changes. Obesity causes an increase in the production of leptin hormone, which may induce cancer, and causes a decrease in the production of adiponectin hormone, which may have anti-cancer effects.²

Adipose tissue is the layer of tissue where the adipocytes are found. Adipose tissue in obese people contains more immune cells that produce proteins that promote inflammation, known as proinflammatory cytokines.³ Some proinflammatory cytokines can activate a protein complex that contributes to genetic mutation, promotes an increase in cell numbers, and prevents cell death.⁴ This can lead to an uncontrollable division of cells, which contributes to cancer development. 

Exercise is a major way to reduce body fat because it enhances the breakdown of triglycerides (type of fat) stored in our adipose tissues. This reduces adipose tissue mass and in turn, reduces leptin production to prevent obesity-induced cancers. Regular exercise also helps lower the production of proinflammatory cytokines, therefore attenuating inflammation and lowering the cancer risk associated with inflammation.⁵ 

Exercise helps regulate metabolism hormones

Insulin is a hormone that signals our body tissues to take up glucose from the blood after meals to prevent high blood sugar levels. Insulin resistance is a condition in which our body tissues are not responsive to the stimulation of insulin, which can lead to type 2 diabetes in the long term. More insulin may be produced by the body to overcome insulin resistance and maintain blood glucose levels. However, an excess of insulin has been suggested to activate a pathway that promotes cell division and prevents cell death, which may lead to cancer development. 

Exercise has been proven to improve insulin sensitivity in muscles and the liver and prevent insulin resistance. Exercising can improve insulin sensitivity by increasing the amount of glucose transporters in body tissues and enhancing the uptake of glucose from blood upon insulin stimulation.⁶ Regular exercise also prevents the overproduction of free radicals in the body, which can damage DNA in the cells and contribute to cancers. Since inflammation caused by obesity can also lead to insulin resistance, exercising helps reduce body fats and prevents insulin resistance and the associated risks for cancers.⁶

Cortisol is a stress hormone that our body produces in response to physical or psychological stress. A temporary increase in cortisol levels due to stress is an automatic response to prepare our body to overcome stress. However, long-term increases in cortisol levels, be it due to chronic stress or health conditions, can actually increase the risk for some cancers, for example, endometrial cancer.⁷ Chronic increase in cortisol levels reduces the immune system’s ability in detecting and removing cancer cells during the early stage. 

Regular exercise can lower the reactivity of cortisol response to stress.^8,9 This helps prevent excess cortisol production during stress which can cause DNA damage and helps tumor development.¹⁰

Remember to wear sunscreen when exercising outdoors

You should apply sunscreen with a sun protection factor (SPF) of at least 15 when you exercise outdoors. This is because exposure to UV radiation for a long period of time can cause damage to the DNA in the cells of your skin. The more you are exposed to UV radiation, the more DNA damage accumulates, and the higher the chance of genetic mutations that may lead to skin cancer. You may need to reapply sunscreen if you are in the sun for more than 2 hours.

Conclusion

Cancer is a group of diseases caused by uncontrolled cell division which may stem from mutations in our genes. Cancer can cause many debilitating complications and in some situations even death, but a healthy lifestyle may help to prevent cancer development. Regular exercise has been suggested to prevent cancer by preventing obesity and obesity-linked conditions that can increase cancer risks. Moreoever, exercise also helps regulate the levels of metabolic hormones, such as insulin and cortisol, which are both associated with cancer risks when they are in excess levels in the body.