While we all know that a significant proportion of cancers are preventable, a recent British study has attempted to quantify the precise percentage of cancers that could be prevented through lifestyle and environmental changes. The authors found that a massive 45% of male cancers and 40% of female cancers could be prevented through simple behavioural changes.
The research, which was led by Professor Max Parkin of the Centre for Cancer Prevention at the Wolfson Institute of Preventive Medicine, involved the identification of 14 factors that are known to be related to cancer risk. These were tobacco use, alcohol consumption, fruit and vegetable intake, meat consumption, fiber intake, salt intake, weight, physical exercise, infections, exposure to ionizing radiation, exposure to UV radiation, post menopausal hormones, breast feeding, and occupation.
In order to calculate the percentage of cancer deaths that could be attributed to each factor, the researchers considered an optimum exposure level – for example, at least 5 servings (400g) of fruit and vegetables a day was considered an optimal level for fruit and vegetable consumption. The researchers then calculated how many cancers would be avoided if the entire population achieved the optimum level for that particular factor, this percentage is known as the population-attributable fraction or PAF.
The graph below shows the percentage of cancers attributable to each of the 14 factors considered in the study.
In total, 42.7% of all cancers were found to be preventable, 45.3% for men and 40.1% for women. The factor most strongly related to cancer risk was found to be tobacco use, which was responsible for 23% of cancers in men and 15.6% of cancers in women. Tobacco is the cause of more than three quarters of lung and laryngeal cancers as well as being a significant risk factor for cancers of the mouth, pharynx, pancreas, kidney, oesophagus, colon, rectum, breast, and bladder.
Other factors that were responsible for a significant percentage of cancers were being overweight (5.5% of all cancers), low intake of fruit and vegetables (4.7%), and excessive alcohol consumption (4.0%). Occupational exposure to hazardous substances such as asbestos was responsible for 4.9% and 2.4% of total cancers in men and women respectively but was a factor in almost 95% of all mesothelioma cases. Excessive salt intake (>6g per day) was responsible for 0.5% of all cancer deaths. High salt diets are known to increase the risk of stomach cancers however this is more of an issue in countries with very high intakes of salt such as Japan.
There is some controversy over the effect of fruit and vegetable intake on cancer risk, with some studies suggesting only a slight reduction in cancer risk. In this study, cancers with a significant proportion attributed to low fruit and vegetable intake included oral cavity and pharynx (56%), oesophagus (46%), larynx (45%), and stomach (36%).
The forms of cancer considered the most preventable are mesothelioma, lung cancer, laryngeal cancer, cervical cancer, oral cancer, and melanoma. Between 85% an 95% of these cancers are the result of modifiable risk factors. Gall bladder cancer, leukemia, and non-hodgkin lymphoma are the forms of cancer considered to be the least preventable.
Studies in other countries have yielded similar results. A Japanese study, published online in the Annals of Oncology last November, found that 53% of male cancers and 28% of female cancers were preventable. The key differences between the two studies were that the percentage of cancers attributable to infections was much higher in the Japanese study (20.6% vs 3.1%), while less cancers in Japan were due to obesity (1.1% vs 5.5%). Just 3.2% of Japanese adults are obese compared to almost a quarter of British adults however rates of Hepatitis B & C as well as Helicobacter pylori infection are much higher in Japan. Hepatitis B & C both increase the risk of developing liver cancer while Helicobacter pylori infection is linked to stomach cancer.
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