Lifestyle causes four out of 10 cancers in the US, new study finds
Smoking, bad diet and drinking alcohol are the top three triggers for the disease. Other research suggests a link between air pollution and smaller sperm, and links inflammation in middle age to dementia
About four out of 10 cancers in the United States are due to lifestyle choices – such as smoking and eating poorly – and other risks that might be avoidable.
The findings were revealed in a study by the journal CA: A Cancer Journal for Clinicians, which calculated “the contribution of several modifiable risk factors to cancer occurrence.”
Factors that are known to raise the risk of cancer included cigarette smoking, excess body weight, drinking alcohol, exposure to second-hand smoke, eating red or processed meats, and low fruit and vegetable consumption, said the report.
Other factors include not getting enough dietary fibre or calcium, lack of exercise, exposure to ultraviolet light and the sexually transmitted infection human papillomavirus (HPV), which can cause cervical and genital cancers as well as tumours in the head and neck region.
Researchers analysed the prevalence of these known risk factors and the extent to which they increase cancer risk, to estimate the proportion of cancers they cause.
Scientists applied these proportions to current cancer data to estimate the number of associated cases and deaths for 26 cancer types.
Of the total 1.57 million cancer cases reported in the United States in 2014, researchers determined that 42 per cent were attributable to these modifiable risk factors.
They found that a similar number of deaths – 45 per cent – could be linked to these factors. The top risk was cigarette smoking, which accounted for 19 per cent of cancer cases and nearly 29 per cent of deaths. Next in line was excess body weight, with 7.8 per cent of cases and 6.5 per cent of deaths.
Alcohol came in third, responsible for 5.6 per cent of cases and four per cent of cancer deaths. UV radiation was estimated to cause 4.7 per cent of cancers and 1.5 per cent of deaths.
Physical inactivity was responsible for almost three per cent of cases and 2.2 per cent of deaths.
Not eating enough fruit or vegetables was linked to almost two per cent of cancer cases and nearly three per cent of deaths. HPV infection – the most common sexually transmitted infection – accounted for almost two per cent of cases and one per cent of deaths.
Two types of cancer were found to have the most number of cases and deaths due to these risk factors – lung cancer and colon cancer.
Better education about cancer prevention and access to preventive health care should be key parts of the battle against cancer in America, the study concluded.
Study links fine particle air pollution with smaller sperm
Men exposed to fine particle air pollution may risk having smaller, abnormally-shaped sperm, a study warned, which “may result in a significant number of couples with infertility.”
An analysis of data from 2001 to 2014 from more than 6,400 Taiwanese men and boys aged 15 to 49, found “a robust association” between a decline in “normal” sperm and exposure to PM 2.5 pollution, it said.
PM 2.5 is the term used for air pollution containing the smallest of particles, those measuring 2.5 microns in diameter or less.
The link was observed for short-term exposure of three months, as well as for long-term exposure of two years, according to study results published in the medical journal Occupational & Environmental Medicine, although outside experts questioned the conclusions.
The research team said every increase of five microgrammes per cubic metre of air in PM 2.5 exposure over two years, was associated with a “significant drop” of about 1.29 per cent in normal sperm shape and size.
Pollution exposure was measured at each participant’s home address using Nasa satellite data.
While sperm shape and size declined, sperm numbers increased, “possibly as a compensatory mechanism,” the researchers found.
A similar correlation was witnessed with PM 2.5 exposure of only three months – how long it takes for sperm to be generated.
The team stressed the link was merely “observational”, which means they cannot definitively state that air pollution was the cause of the decline in sperm size.
Allan Pacey, a professor of andrology at the University of Sheffield who was not involved in the study, says sperm size and shape is notoriously hard to assess, and the effects on infertility unclear.
“So, while the authors have found a potentially interesting biological result, I am not sure that it is clinically meaningful.”
For Kevin McConway of The Open University in England, other factors not taken into account by the researchers may be responsible for the sperm changes.
“So there has to remain doubt as to whether particulate pollution, or indeed any kind of air pollution, is a cause of semen abnormality,” he says.
“If I were young enough to worry about my fertility, I wouldn’t put moving to an area with cleaner air at the top of my list of actions – though there are certainly many other health-related reasons to live in cleaner air.”
Dementia-inflammation link possible, study suggests
People who show signs of inflammation in middle age are more likely to suffer from brain shrinkage later in life, a possible precursor to dementia or Alzheimer’s disease, say researchers.
The findings in the journal Neurology are the latest to uncover an association between dementia and inflammation, in which the body’s immune cells rev up in response to influences like smoking, stress, illness or poor diet.
However, the findings stopped short of proving any cause-and-effect relationship.
“These results suggest that inflammation in mid-life may be an early contributor to the brain changes that are associated with Alzheimer’s disease and other forms of dementia,” says study author Keenan Walker of the Johns Hopkins University School of Medicine.
“Because the processes that lead to brain cell loss begin decades before people start showing any symptoms, it is vital that we figure out how these processes that happen in middle age affect people many years later.”
The study was based on 1,633 people with an average age of 53.
Researchers tested their blood for levels of five markers of inflammation – not in any specific part of the body but rather throughout it – including the white blood cell count.
An average of 24 years later, participants took a memory test and underwent brain scans.
Those who had higher levels of inflammation on three or more biomarkers had an average five per cent lower brain volume in the hippocampus and other areas associated with Alzheimer’s disease.
The effect was similar to having one copy of a gene – called apolipoprotein E (APOE) e4 – that predisposes people to Alzheimer’s, say the researchers.
People with higher inflammation also performed slightly worse on a memory test, remembering on average five out of 10 words they were asked to recall, compared to 5.5 in the non-inflammation group.
Outside experts described the study as large and rigorously conducted, but stressed that it did not study whether patients went on to develop Alzheimer’s disease, only that some showed signs of brain shrinkage and memory loss.
“This research points to inflammation as a potential early indicator of later brain degeneration, but we cannot say whether inflammation could be causing brain shrinkage or if it is a response to other damaging processes that might already be underway,” said Carol Routledge, director of Research at Alzheimer’s Research UK.
“The researchers measured levels of inflammation at a single point in time and we don’t know whether this gives a reliable indication of inflammation more generally,” she adds.
Doug Brown, director of research and development at the Alzheimer’s Society, said the findings are in line with a growing body of research that points to inflammation and problems with the immune system playing a role in the development of dementia.
“Although these results are a helpful addition to the wider body of research around brain health and inflammation, what we need is more research to further clarify this relationship,” he says.
“While the study may not conclusively show that brain shrinkage is due to inflammation, it does highlight the importance of taking care of your cognitive health throughout your life, particularly in middle age,” he adds.
“This includes eating a healthy balanced diet, taking regular exercise and managing conditions like diabetes and high blood pressure.”