Knowledge of risk factors in cancer

Many modifiable risk factors for cancer have been reported, including: smoking, estimated to cause one-third of UK cancers;1 obesity; low intake of fruit and vegetables, and physical inactivity, estimated to cause approximately 3% and 2% of cancers respectively;2 excessive alcohol use, accounting for about 4% of cancers, and excess exposure to sunlight. Public knowledge of these risk factors is little known, as surveys have generally concentrated on specific cancers;3^,4 or been relatively small.

We performed a survey in eight general practices in Northern England. Adult patients attending in December 2007 or January 2008 were asked to select six from 12 possible risk factors. As well as the six risk factors, we included six false ones: 1556 questionnaires were returned. The mean number of risk factors selected was 5.6. Results are shown in Table 1.

The virtue of this survey is its simplicity and its size. These are weaknesses too: in that we chose not to request details such as sex or age. However, little difference between the sexes was identified before.4 In a previous survey of 1000 women enquiring about risk factors for breast cancer two-thirds identified a positive family history, yet only 14% identified age, 19% hormone replacement therapy, and 12% oral contraception.3 An older survey asked about 10 true and four false causes, similar to this current survey.4 Smoking results were similar, with 93% identifying a relationship between smoking and lung cancer; likewise, 42% linked a diet low in fruit and vegetables with bowel cancer. Responses for obesity were much lower, with 46% of females linking this with breast cancer, yet only 13% of males doing so: this compares with 70% identifying overweight in the current survey.

Our results suggest publicity about smoking has worked. Similarly, excess sun exposure, excess alcohol use, and being overweight are now generally recognised as risk factors. Less encouraging was the relatively low level of knowledge about diet and exercise. This suggests a new direction for cancer prevention campaigns. A significant proportion considered both traffic fumes and microwaves to be risk factors. Although scientific evidence does not support these, both have also had considerable media coverage. How this can be countered is less clear: some of the population distrust much of the information they receive from ‘official’ sources.5 Maybe these erroneous cancer beliefs are less important at an individual level – as avoidance of microwaves or traffic fumes is very unlikely to be harmful.

• © British Journal of General Practice, 2008.