Wednesday December 7 2011
Smoking was responsible for 19% of new cancer cases
In 2010, around 43% of cancer cases seen in the UK were caused by lifestyle and environmental factors, according to several news sources today. This equated to around 134,000 cancers caused by potentially avoidable behaviours such as smoking, drinking alcohol and eating a poor diet.
The news is based on an extensive report that has estimated how lifestyle factors can influence a range of cancers. Tobacco smoking was the biggest risk factor for cancer, responsible for over 19% of all new cases. Other factors included being overweight (5.5% of cases), having a poor diet (9.2%) and drinking too much alcohol (4%). As cancers usually have multiple causes, these figures do not mean that we can identify specific people whose cancer was caused by each of these factors, but they can help to estimate how many cases could be prevented by cutting out all of these harmful factors.
“Many people believe cancer is down to fate or ‘in the genes’ and that it is the luck of the draw whether they get it,” said Professor Max Parkin, the report’s main author and an epidemiologist at Queen Mary University of London. “Looking at all the evidence it’s clear that around 40% of all cancers are caused by things we mostly have the power to change.”
This new study of the link between cancer and lifestyle is one of the most comprehensive to date. Undertaking these lifestyle changes could also have a positive impact on other major diseases such as heart disease, stroke and diabetes.
Where did the story come from?
The study was carried out by Professor Parkin from the Centre for Cancer Prevention at the Wolfson Institute of Preventive Medicine. It was funded by the charity Cancer Research UK. The study was published as part of a special British Journal of Cancer supplement looking at various aspects of the UK population’s cancer risk.
The research was covered fairly by the media, helped by a clear Cancer Research UK press release explaining the extensive data and findings. However, the Daily Mail’s coverage suggesting that four in 10 cancers could be prevented by simply “tweaking” or making “small” changes to lifestyle is questionable, as the changes would need to be quite significant, such as giving up smoking altogether rather than simply cutting down.
The study makes the valid point that certain lifestyle changes are easier to achieve than others. For example, it says that eating five or more servings of fruit and vegetables a day is a relatively modest change, while giving up smoking is harder to achieve. Another example is long-term weight loss, which is particularly difficult to sustain.
Several other papers also reported that 40% of cancer cases could be avoided by lifestyle changes, but as the authors of a summary chapter point out, an estimate of reduction in cancer cases based on lifestyle changes would have to take into account what is realistically achievable within a reasonable timeframe.
Furthermore, there are uncertainties around some of the estimates and difficulties in modelling future scenarios, which means that the study should be viewed as general guide, and not a precise indicator of the number of cancer cases that could be prevented by lifestyle changes. For example, it’s hard to estimate how factors such as a former smoker’s smoking history will affect their future risk.
What kind of research was this?
This was an epidemiological study that aimed to estimate the percentage of cancers (excluding non-melanoma skin cancer) in the UK in 2010 which could be attributed to certain lifestyle, environmental and dietary risk factors. It looked at 14 such risk factors, most of them modifiable.
What did the research involve?
The researchers compiled a total of 14 lifestyle and environmental factors for which there is good evidence from high quality studies of a likely causal association with cancer:
- four elements of diet (consumption of red and processed meat, fruit and vegetables, fibre and salt),
- being overweight
- lack of physical exercise
- radiation (ionising and solar)
- use of hormones after menopause (such as in HRT)
They set for each of these factors an “optimum” exposure level, below which was considered a risk. For example, optimum intake of fruit and vegetables was set at five servings or more a day, with a lower intake considered to be a risk. The optimum level of smoking was nil exposure, while breastfeeding was set at a minimum of six months.
The researchers then examined high-quality research – systematic reviews and meta-analyses – for information on the risks of exposure to these factors and data on their prevalence within the general population. Using the projected number of cases for various types of cancer in the UK population in 2010, they calculated the “population attributable fraction” for each risk factor and its relative contribution to the total numbers of cancers diagnosed in the UK that year. This fraction can be thought of as the proportion of cancer cases that could be avoided if a particular risk factor was removed. Because of the way it is calculated and because cancers have multiple causes, it isn't possible simply to add up the separate population attributable fractions to produce a total.
What were the basic results?
The study found that, overall, four key lifestyle factors accounted for 34% of cancers in 2010:
- tobacco: 19.4%
- diet: 9.2%
- being overweight or obese: 5.5%
- alcohol: 4%
These factors individually add up to more than 34% but should not simply be viewed cumulatively as most cancer is caused by more than one of these factors. Smoking was associated with large increases in the risk of cancers of the lung, mouth, throat, windpipe and foodpipe, as well as smaller increases in the risk of many other cancers.
Other risk factors included:
- occupation (3.7%), for example a job that exposes someone to asbestos
- UV radiation caused by excessive exposure to sun or sunbeds (3.5%)
- infections (3.1%)
- excess intake of red and processed meat (2.7%)
- lack of physical exercise (1%)
- breastfeeding for less than six months (0.5%)
- use of post-menopausal hormones (0.5%)
Smoking was the single biggest risk factor for both men and women. After this, the importance of different risk factors differed by sex.
For men, the three biggest risk factors after smoking were:
- lack of fruit and vegetables (6.1%)
- occupation (4.9%)
- alcohol (4.6%)
For women they were:
- being overweight or obese, which is linked to breast cancer (6.9%)
- infection (3.7%)
- UV radiation (3.6%)
- alcohol (3.3%)
- lack of fruit and vegetables (3.4%)
The researchers emphasised that some cancers are caused by more than one factor.
How did the researchers interpret the results?
The researchers pointed out that, for the most part, the lifestyle and environmental factors linked to cancer are avoidable (apart from ionising radiation). Tobacco smoking was found to be by far the most important avoidable cause, followed by unhealthy diet (especially a lack of fruit and vegetables), excess body weight and alcohol. The researchers said the study will “help focus the attention of researchers, individuals and policy makers on the relative importance of the currently known causes of cancer”.
However, the researchers said that due to the difficulty in making certain estimates and a lack of data in certain areas, there are several “sources of uncertainty” around the estimates given. Because of this, they said these estimates should not be used uncritically to measure the percentage of cancers that could be avoided by preventive measures.
What does this mean for me?
This study indicates the relative importance of certain lifestyle factors in increasing the risk of cancer. Factors such as a poor diet, smoking, being overweight and drinking too much are already known to increase the risk not only of cancer but also of a range of serious chronic conditions such as cardiovascular disease, diabetes, and kidney and liver problems. This study provides another good reason for people to live a healthy lifestyle.
It’s important to note, however, that the individual risk of different cancers depends not only on lifestyle but on other factors including genetic make-up, family history and getting older. Leading a healthy lifestyle is not a cast-iron guarantee against cancer, but it does reduce the risk of getting it.