We don’t know what causes most cases of acute lymphoblastic leukaemia. But there are some factors that may increase your risk of developing it.
What a risk factor is
Anything that can increase your risk of getting a disease is called a risk factor.
Different cancers have different risk factors. Having one or more of these risk factors doesn't mean you will definitely get that cancer.
Having one or more risk factors doesn't mean that you will definitely get leukaemia.
We’ve known for a long time that exposure to very high levels of radiation increases acute leukaemia risk. For example, people exposed to the atomic bomb explosions in Japan at the end of World War 2 had higher rates of leukaemia. A 20 year study has followed up workers who helped clean up after the Chernobyl nuclear power plant accident in 1986. It shows that even at low doses of radiation there is an increased risk of all types of leukaemia.
Some people worry that childhood x-rays cause leukaemia in children. A large study found there is very little evidence of any increase in risk, except in a type of leukaemia that is rare in children, called pre B cell ALL (or pre B ALL). But the researchers say that even this could be a chance finding and not a real risk increase.
There is some evidence that x-rays during pregnancy can increase risk of childhood leukaemia. So doctors avoid x-rays for pregnant women whenever possible.
Radon is a naturally occurring radioactive gas which can build up in houses in some areas of the UK. A Danish study has shown a higher risk of ALL in children living in houses with the highest levels of radon.
A CRUK study showed that natural background radiation increases the risk of leukaemia in children and adults. The background radiation comes from cosmic rays, rocks and soil as well as food and drinking water. But it is important to remember that this risk is very low.
Exposure to a chemical called benzene at work increases the risk of developing ALL. Exposure to benzene may occur in petrol, chemical, pharmaceutical and rubber industries. Benzene is also used in shoe production and the printing industry. The higher the level of exposure over many years, the greater the risk. There is benzene in traffic pollution but the levels are likely to be too low to increase leukaemia risk.
Benzene is also in cigarette smoke. People who smoke tobacco with shisa pipes are exposed to higher levels of benzene.
A review of studies (meta analysis) in 2009 has shown that smoking in the home by parents may increase the risk of ALL in their children. This includes smoking by the father in the time before conception. Data from the French ESCALE study in 2013 suggests that drinking more than 2 cups of coffee a day during pregnancy may slightly increase the risk of childhood ALL.
Certain rare, inherited conditions can increase the risk of acute leukaemia, including:
- down’s syndrome
- fanconi anaemia
- ataxia telangiectasia
People have a slightly increased risk of developing ALL many years later who have treatment with the chemotherapy drugs:
The risk depends on how much treatment you had. It's important to remember that this risk is still very small compared to the risk to your health if the cancer had not been treated.
We know that a virus called HTLV-1 (human T cell leukaemia virus) increases the risk of developing a rare type of adult T cell leukaemia.
You may read in the press from time to time that some people are concerned about power lines and risk of cancer. Power lines produce high levels of 'low frequency electromagnetic radiation' (EMR).
Although some studies seem to suggest that exposure to very high levels of EMR could increase childhood leukaemia risk, the findings are not very clear. We don’t really know if the childhood leukaemia in these studies was actually caused by low frequency EMR. It could be due to some other common factors, or even chance. Scientists agree that we need more research before we can say for sure one way or the other.
A UK report in February 2014 found that children who live near overhead power lines in early life do not have a greater risk of developing childhood leukaemia. The report is from the Childhood Cancer Research Group at the University of Oxford. The researchers looked at nearly 16,500 children diagnosed with leukaemia since the 1990s who lived within a kilometre of overhead power lines.
They say that there is no direct biological effect of power lines on leukaemia risk. More research will continue.
Some studies show that people who are very overweight (obese) have a slightly higher risk of leukaemia than people with a normal bodyweight.
One study has shown a slightly higher risk of childhood ALL after exposure to paints, but more studies are needed to back up this finding.
An overview study (combined analysis) looked at published research into people with HIV or AIDS, or people treated with medicines that lower immunity after an organ transplant. The researchers found that these people have a risk of leukaemia that is double or triple that of people without these factors.
Other possible causes
Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.
Factors that may lower the risk of ALL
Researchers have pulled together the results of 17 separate studies. This showed that breastfed children have a very small reduction in ALL risk, compared to children who had not been breastfed.
Exposure to infection in childhood
Studies show that children who go to nurseries or childminders from a young age have a lower risk of acute lymphoblastic leukaemia. The lower risk in these children may be due to exposure to infections. Children may have a slightly increased risk of ALL if they do not come across common infections from birth, but are exposed to them later in life.
A few studies have shown an increased risk for children of mothers who tested positive for Helicobacter pylori or Epstein Barr virus during pregnancy. These are both common infections and we need more research before we can be clear whether or not this is a risk factor for childhood leukaemia.