Tuesday March 19 2013
A combination of exercise and a healthy diet lowers cancer risk
'The seven golden rules for a healthy life: Simple lifestyle steps can help prevent cancer and heart disease,' the Mail Online website reports. This accurate headline comes from a new study that found that people who took steps to reduce their heart disease risk also had a lower risk of developing cancer. These seven factors, drawn up by the American Heart Association (AHA) in 2010, were designed as an easy way for people to understand the best ways of avoiding cardiovascular disease (CVD), such as heart disease.
In this large long-term study, researchers found that cancer risk was lower among people who met the ideal levels for each of the seven factors. For example, people who achieved ideal levels for six or more factors had a 51% reduced cancer risk. Having just four of the factors at ideal levels still reduced cancer risk by 33%.
While this is welcome news, it is worth noting that smoking appeared responsible for the majority of the associations seen between the seven factors and cancer risk. However, even after excluding smoking, having ideal levels for more factors was associated with a reduced risk of cancer.
Where did the story come from?
The study was carried out by researchers from Northwestern University (Chicago), the University of Minnesota, and a number of other US research institutions. It was funded by the US National Heart, Lung and Blood Institute, the state of Maryland, the Maryland Cigarette Restitution Fund, and the National Program of Cancer Registries.
It was published in the peer-reviewed journal Circulation which has been made available on an open access basis.
This story was covered well by The Daily Telegraph, Daily Express and the Mail Online website. The Mail Online helpfully provides background information on previous studies related to each of the seven factors.
The Daily Telegraph introduced the story with a quotation from Professor Jean-Pierre Després, scientific director of the International Chair on Cardiometabolic Risk, who said that only one in every 1,000 (0.1%) people in the developed world have ideal levels for all of the seven factors. The current study also found that only 0.1% of participants had ideal levels of all seven factors.
What kind of research was this?
This was a cohort study that followed people for between 17 and 19 years to see if maintaining ideal levels of seven health factors proposed by the AHA to promote cardiovascular health also reduced the risk of cancer.
The seven health factors and their ideal levels are:
- physical activity – at least 75 minutes per week of vigorous physical activity, or 150 minutes per week of moderate or moderate plus vigorous activity
- healthy body mass index (BMI) – less than 25kg/m2
- diet – having four to five components of a healthy diet score
- cholesterol – total cholesterol less than 200mg/dl
- blood pressure – less than 120mm Hg systolic and 80mm diastolic
- blood sugar – fasting levels of glucose less than 100mg/dl
- smoking – never smoking, or quitting more than 12 months ago
This study was a large cohort study with a long follow-up period. As with all cohort studies, this study cannot prove that maintaining ideal levels of the seven factors – referred to in the press as the 'seven golden rules' – is the only thing that causes a reduction in cancer risk. The presence of other factors that could also be responsible for the association (confounders) cannot be excluded.
A randomised controlled trial would be required to prove a direct causal effect, and would need to be designed with care. Given what we know about healthy lifestyles, it would be unethical to randomise people to smoking, no exercise, and bad diet.
What did the research involve?
The researchers analysed information for 13,253 white and African American participants in a large US cohort study (the Atherosclerosis Risk In Communities study). Participants were aged between 45 and 64 at the start of the study, and only people who did not have cancer when the trial started were considered in this study. Participants were followed-up for between 17 and 19 years.
The researchers looked to see whether baseline measurements for the seven health behaviours and factors were associated with the risk of developing cancer.
Each participant's diet was assessed using a food frequency questionnaire. Physical activity was also reported using a questionnaire, and smoking status was derived from interviews. Blood samples were taken to measure cholesterol and glucose levels. Blood pressure, weight and height were also measured.
Information relating to cancer that developed during follow-up was obtained from cancer registries and hospital surveillance.
All types of cancer – except non-melanoma skin cancer – were combined. Non-melanoma skin cancer was excluded because the main risk factor for the development of this type of cancer is exposure to sunlight or UV light, which is different from most other types of cancer.
What were the basic results?
At the start of the study:
- 71.5% of participants did not smoke
- 33.2% had ideal BMI
- 26.9% had ideal cholesterol levels
- 5.3% had ideal diet
- 37.9% had ideal levels of physical activity
- 51.8% had ideal levels of blood sugar
- 41.6% had ideal levels of blood pressure
Most people had ideal levels of two or three health factors. Only 16 people (0.1% of all participants) had ideal levels of all seven health factors, while 371 (2.8%) did not have ideal levels for any of the factors.
During the follow-up, 2,880 people were diagnosed with cancer. As the number of factors that participants had ideal levels of at baseline increased, the risk of developing cancer during the follow-up fell.
Compared with people who had no ideal levels of the seven factors:
- people who had ideal levels of six or seven of the factors (2.7% of participants) had 51% lower risk of cancer (hazard ratio (HR) 0.49, 95% confidence interval (CI) 0.35 to 0.69)
- people who had ideal levels of five factors (8.8% of participants) had 39% lower risk of cancer (HR 0.61, 95% CI 0.48 to 0.79)
- people who had ideal levels of four factors (17.8% of participants) had 33% lower risk of cancer (HR 0.67, 95% CI 0.54 to 0.84)
- people who had ideal levels of three factors (26.3% of participants) had 26% lower risk of cancer (HR 0.74, 95% CI 0.59 to 0.91)
- people who had ideal levels of one or two factors (41.6% of participants) had 21% lower risk of cancer (HR 0.79, 95% CI 0.64 to 0.98)
When smoking was excluded, participants who had ideal levels of five or six of the remaining factors had 25% lower risk of cancer than those who did not have ideal levels of any of the factors.
How did the researchers interpret the results?
The researchers conclude that having ideal levels of the seven factors and behaviours proposed by the American Heart Association (physical activity, body weight, diet, cholesterol, blood pressure, blood sugar and smoking) is associated with a reduced development of cancer.
This was a very large study. It found that having ideal levels (defined by the American Heart Association) of seven factors and behaviours was associated with a reduced risk of cancer. These factors include smoking, diet, physical activity, BMI, cholesterol, blood sugar and blood pressure.
However, it seems that a large proportion of the association was due to one behaviour: smoking. It represents further proof, if any more is required, of how smoking can harm multiple aspects of your health, such as your heart, blood pressure, circulation and individual risk of developing cancer.
This study has several strengths, including its size and length of follow-up. However, it also has several limitations, most of which were noted by the authors.
- The researchers did adjust for age, sex, race and location when performing their analyses, but they say they did not adjust for a number of other factors that could explain the association (confounders), such as socioeconomic status or other cancer risk factors. However, because we already know about these behaviours and risk factors, this may not be an important limitation.
- Health behaviours and factors were only measured once, at the start of the study, and could have changed during the long period of follow-up. In addition, some variables, such as diet and exercise, were self-reported by participants, rather than being objectively measured. Both of these things may have reduced the accuracy of the measurement.
- The study only included white and African American people, so its results may not be entirely applicable to other ethnic groups. But, again, given what is known about these behaviours and risk factors, this may also not be an important limitation.
Although these goals were drawn up to prevent cardiovascular disease, in this study they have been shown to be associated with a reduced risk of cancer. It is likely that they are also associated with a reduced risk of other chronic diseases too.
This study reinforces what is already known about health and cancer risk, but adds useful numbers showing the effect of tackling several things together. The message is clear: not smoking, maintaining a healthy weight, staying physically active and maintaining ideal levels of cholesterol, blood sugar and blood pressure is beneficial for long-term good health.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.