What causes cancer?

20th August 2021

Cancer is caused by genetic mutations that accumulate over time in the DNA of a cell. These mutations can be caused by lifestyle and environmental factors, as well as occurring by random chance. Together, these factors all contribute to the development of cancer. But what exactly increases our chance of getting cancer?

What increases your risk of cancer?

For most people the biggest risk factors for cancer are things we can't do anything about - aging and having a family history of cancer. The older you are the more likely you are to develop cancer. And if cancer runs in your family, you are at greater risk of developing cancer. However, it's estimated that only 1 in 10 cases of cancer are caused by a family history of the disease. 


Do lifestyle choices cause cancer?

There are many things that we're told to avoid because they cause cancer. But the things we know for sure to do to lower our risk of cancer are:

Not smoking - Smoking is the biggest preventable cause of cancer in the world and is the number one cause of lung cancer, responsible for around 7 out of 10 cases in the UK. Not smoking at all is one of the most important things someone can do to reduce their chance of getting cancer.

Maintaining a healthy weight - It is thought that about 1 in 20 cancers are linked to obesity, and the longer you are overweight for and the more weight you carry, the higher the risk is – though it is important to remember that not everyone who is obese will develop cancer in their lifetime, and being a healthy weight does not preclude you from developing it either.

Eating a balanced diet - Despite what you may have read online, there is no food that will cause or prevent cancer. The best way to reduce your risk of cancer is to eat a healthy, well-balanced diet. This will also help you maintain a healthy weight, which will also help reduce your risk of cancer.

Do lifestyle choices cause cancer?

Being physically active - Physical activity has been shown to reduce your risk of cancer although the exact mechanism is unclear. It is likely due to a combination of effects that are directly caused by being active and knock-on effects such as helping to maintain a healthy weight.

Limiting how much alcohol you drink - All the best available evidence (for which there is a lot) tells us that drinking alcohol causes seven types of cancer. It doesn’t matter what you drink and it doesn’t matter how you drink it. Alcohol is a carcinogen. Alcohol causes cancer.

Protecting yourself from the sun - It's important to wear sunscreen and avoid prolonged periods of direct exposure to the sun because it can increase your risk of developing skin cancer.

For a cancer cell to develop, several genetic mutations need to happen. And these mutations need to happen in genes that control when, and how much, cells divide. Mutations to these genes cause cells to divide in an uncontrolled way, one of the hallmarks of cancer.

But what causes these genetic mutations?

Things inside and outside our body can cause genetic mutations. The natural processes of life generate molecules that damage DNA and cause mutations. The good news is that our cells have evolved repair kits to fix mutations and prevent cancer from developing.

Things in our environment and our lifestyle can also cause genetic mutations. UV rays from the sun can penetrate through our skin, into cells and damage DNA. Tobacco smoke contains chemicals that enter cells in our lungs and cause damage to DNA. Obesity or being overweight can cause changes in the level of hormones in our body. This can lead to cells dividing more than they should. And the more a cell divides the more it puts itself at risk of picking up genetic mutations.

Our cells can repair many of the mutations caused by these things. But continued exposure over a long period of time can cause more damage than our cells can cope with. And this is when genetic mutations emerge that can cause cancer.

Some types of cancer are also caused by infection with a virus, such as the cervical cancer virus, HPV. This virus enter cells and produces proteins that tell the cell to divide in an uncontrolled way. Thanks to research, we now have a vaccine against HPV. This vaccine has led to cervical cancer cases plummeting in countries around the world.

There are important things you can do to reduce your chances of developing cancer. Don't smoke, avoid spending too much time in the sun, and maintain a healthy weight through a balanced diet and regular exercise. But remember, everyone is different, and every cancer is different, so there is no magic bullet.

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Further reading

Cancer explained
Cancer explained

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