Friday May 20 2016
A few hours exercise a week can cut cancer risks
"Half of all cancer deaths could be avoided if people simply adopted a healthier lifestyle," the Daily Mail reports.
A new study adds to the weight of evidence that says combining simple lifestyle changes can dramatically cut cancer death rates.
More than 100,000 health professionals from the US were asked to complete questionnaires about their lifestyle and cancer status every two years, and diet every four years.
The researchers compared cancer rates between people with low- and high-risk lifestyle factors, and also compared rates in the low-risk group with the general white population in the US.
They found a large number of cancer cases and deaths could be attributed to a high-risk lifestyle, such as an individual being overweight, smoking, drinking heavily, or being physically inactive.
The researchers estimated between a quarter and a third of all cancer cases in this population group could be attributed to poor lifestyle factors.
These findings are in agreement with past research and the understanding that a healthier lifestyle may reduce the risk of various types of cancer.
But this study has limitations, including the population group, which only involved white American health professionals, and the possibility that the estimates are inaccurate.
The study would appear to confirm that any small lifestyle changes you can make, such as quitting smoking, could considerably reduce your risk of developing cancer. And the more of these small changes you can combine, the greater the effect.
Read more about how lifestyle changes can help prevent cancer.
Where did the story come from?
The study was carried out by researchers from Harvard Medical School and was funded by the US National Institutes of Health.
It was published in the peer-reviewed journal, JAMA Oncology.
The Daily Mail reported on the study fairly accurately, but did not present any of its limitations.
It's nice to see that the article included clear recommendations from the research team about how a person can reduce their risk of cancer.
However, the headline figure of "half of all cancer deaths" seems a bit of a fudge, as the study presented a range of different results for specific cancer types.
What kind of research was this?
This prospective cohort study followed a large population group over time, and assessed the incidence of cancer and related deaths.
The researchers looked at how these cancer outcomes were related to various lifestyle factors, and then estimated the proportion of cancers that could be attributed to these factors.
The observational nature of this type of study means it is not able to prove causation, but it can find links and potential risk factors.
This type of study has strengths in terms of being able to follow a large number of participants over a long period of time, but the number of people who become non-responsive to follow-up assessments may increase over the years.
What did the research involve?
The researchers recruited participants from two cohort studies:
- The Nurses' Health Study – which started in 1976 and enrolled female nurses aged 30 to 55
- The Health Professionals Follow-up Study – which started in 1986 and enrolled male health professionals aged 40 to 75
Participants completed questionnaires about their medical history and lifestyle at the beginning of the study and every two years thereafter. Dietary information was collected every four years using a validated food frequency questionnaire.
The researchers split the participants into two groups according to the level of health risk associated with their lifestyle.
To be considered low risk, a participant had to meet the following requirements:
- have never smoked or be a past smoker more than five years ago
- drink no or a moderate amount of alcohol – no more than one drink a day for women and two for men
- have a body mass index (BMI) of at least 18.5 and lower than 27.5
- do at least 75 minutes of vigorous-intensity or 150 minutes of moderate-intensity aerobic physical activity a week
If all of these requirements were not met, the participant would be considered high risk.
The outcomes of interest were the incidence of total and major individual cancers and associated deaths. Cancer was self-reported in the questionnaires. Where a participant failed to respond, the National Death Index was used to identify deaths.
The researchers compared the cancer rates between the low- and high-risk groups. They then compared cancer rates in the low-risk group with cancer rates in the general population using national surveillance data.
They used this information to help them calculate population-attributable risk (PAR).
This is an estimate of the proportion of all cancer cases that can be attributed to poor lifestyle factors, or the number of cancers that would not occur in a population if the risk factor – in this case, a high-risk lifestyle – was eliminated.
For example, a PAR could be used to estimate how many people in a given population would not die of lung cancer if nobody in that population smoked.
What were the basic results?
A total of 135,910 people were included in the study (89,571 women and 46,339 men). The low-risk group contained 21% of all participants (12% women and 9% men) with the remaining 79% classed as high risk (54% women and 25% men).
The incidence of cancer per 100,000 people was 463 for women and 283 for men in the low-risk groups, compared with 618 for women and 425 for men in the high-risk groups.
From this, the researchers estimated that 25% of cancers in women and 33% of cancers in men could be attributed to high-risk lifestyle factors. For cancer-related deaths, 48% of cancer deaths in women and 44% of cancer deaths in men could be attributed to a high-risk lifestyle.
For individual cancers, the proportion of cancers estimated to be caused by high-risk lifestyle factors were:
- lung – 82% for women, 78% for men
- bowel – 29% for women, 20% for men
- pancreas – 30% for women, 29% for men
- bladder – 36% for women, 44% for men
Estimates were similar for cancer death, though there were additional associations for some other sites, including breast (12%), womb (49%), kidney (48% in men), and oral and throat (75% in women and 57% in men) cancers.
The general US populations were at higher risk than the whole study population, meaning that the PARs for these cancers resulting from a poor lifestyle were even higher than the researchers' estimates – for example, the PAR for bowel cancer jumped to 50%.
How did the researchers interpret the results?
The researchers concluded that, "In this cohort study of a portion of the US white population, about 20-40% of cancer cases and about half of cancer deaths can be potentially prevented through lifestyle modification.
"These figures increased to 40-70% when assessed with regard to the population of US whites, and the observations are potentially applicable to broader segments of the US population."
This prospective cohort study assessed the number of cancer cases and related deaths associated with poor lifestyle factors in a sample of US health professionals.
As the findings demonstrate, a large number of cancer cases and deaths in both men and women can be attributed to a high-risk lifestyle, such as being overweight, smoking, drinking heavily, or being physically inactive.
Worryingly, a poor lifestyle was estimated to account for an even greater number of cancers in the general population.
These findings are in agreement with much research, which has found that a healthier lifestyle may reduce the risk of various cancers.
The study has both strengths and limitations to consider. It contained a large number of participants and excluded types of cancer where incidence may be related to environmental factors rather than lifestyle, both adding strength to the findings.
It did have limitations, however:
- The use of questionnaires for collecting information is prone to bias, either by people reporting what they think they should be doing rather than what they are doing, or because of difficulty recalling information over a period of time.
- Only medical professionals were included in the study. This group are potentially more health conscious, so may not be a good reflection of the whole population. This is supported by the fact that even the high-risk study group were healthier than the US population overall, and PAR estimates for cancer from poor lifestyle factors were higher in the general population.
- Only including a white population means these findings may not necessarily apply to other ethnicities.
- These results are only estimates: though informed by careful analysis of this population and their lifestyle factors and cancer rates, it's possible that the proportion of cancers attributed to poor lifestyle factors is inaccurate, particularly for wider populations.
Despite these limitations, it is well known that unhealthy lifestyle factors could increase your risk of developing cancer, as well as various other health problems. Any small changes you can make to your lifestyle could considerably reduce your risk.
Read more about how to prevent cancer.