Tuesday January 8 2008
Five portions of fruit and veg a day is a healthy behaviour
“Healthy life 'can give you another 14 years'” according to a headline in The Daily Telegraph. The report underneath explains that “four healthy behaviours – not smoking, exercising, alcohol intake of less than 15 units per week (less than five large glasses of wine or five pints of medium-strength lager) and having vitamin C levels equivalent to eating five servings of fruit and vegetables a day” can increase lifespan.
The newspaper story is based on results from a large study looking at 20,244 people living in Norfolk that compared people who had all four of these healthy behaviours with people who had none. Those with all four had the same risk of dying as someone who was 14 years younger. The message that a good diet and exercise, and not smoking or drinking too much is good for you, and can extend your life will not be a surprise to most people.
Where did the story come from?
Dr Kay-Tee Khaw and colleagues the University of Cambridge School of Clinical Medicine and the Epidemiology and Dunn Nutrition Unit of the Medical Research Council carried out this research. The study was funded by the Medical Research Council, Cancer Research UK, the Stroke Association, the British Heart Foundation, Research Into Ageing, and the Academy of Medical Science. It was published in the peer-reviewed medical journal: PLoS Medicine.
What kind of scientific study was this?
This was a prospective cohort study – the European Prospective Investigation into Cancer and Nutrition (EPIC) Norfolk study – which aimed to look at the effects of nutrition and other health behaviours on cancer and other diseases. The researchers enrolled 20,244 people aged 45–79 who were registered with a GP in Norfolk and who reported that they did not have cancer or heart disease, between 1993 and 1997. These people were asked to complete questionnaires about themselves, their health, and their lifestyle. The questionnaire asked what their weekly alcohol intake was, whether they smoked now or in the past, whether they had a physically active job, and how many hours they spent in non-work physical activity. Participants were examined by a nurse, who measured their weight and height, and took a blood sample. Blood samples were tested for vitamin C levels, as an indicator of whether the person was eating enough fruit and vegetables.
For this study, people were given one point for having healthy behaviours on four measures
- not smoking currently;
- being physically active;
- having moderate alcohol intake; and
- having vitamin C levels equivalent to having five servings of fruit and vegetables a day.
Moderate alcohol intake was defined as one to 14 units of alcohol a week, and physical inactivity was defined as having a sedentary job and less than 30 minutes a day recreational physical activity.
Researchers then followed people until 2006 (an average of 11 years) by checking national records to see if they died and, if they did die, what was the cause. They then compared the risk of death for people who had each of these four health behaviours (both individually or combined) with people who did not have these behaviours. These analyses were adjusted to take into account factors that might affect risk of death such as gender, age, body mass index, and social class at enrolment.
What were the results of the study?
The researchers found that each of the healthy behaviours on their own reduce the risk of dying, with not smoking having the largest effect. The more of the four healthy behaviours a person had, the more it reduced their risk of dying over the 11 years of follow up. People who had none of the four healthy behaviours (those who smoked, were sedentary, had excess alcohol intake, and not enough vitamin C) were four times more likely to die than those who had all four healthy behaviours.
Researchers estimated that the average risk of death for people with all four healthy behaviours was equivalent to the risk of death in people who were 14 years younger. When the researchers separated out deaths by cause, they found that this trend was largely caused by the healthy behaviours reducing deaths from cardiovascular causes.
What interpretations did the researchers draw from these results?
The researchers concluded that people who exercise, have moderate alcohol intake, have a good intake of vitamin C, and do not smoke, have an impact on their lives, which is equivalent to 14 years of chronological age compared with people who do not have the healthy behaviours.
What does the NHS Knowledge Service make of this study?
This was a large prospective study. The size and prospective nature of the study increases the reliability of its results. Although we can confidently say that having these four healthy behaviours is associated with a significant difference in total mortality, it is difficult to attribute an exact number of years due to this effect, and the figure of 14 years should be taken as an estimate.
- People who have certain “health seeking behaviours”, such as the four behaviours assessed in this study, tend to have other health seeking behaviours. This means that people who exercise, have moderate alcohol intake, have a good intake of vitamin C in the diet, and do not smoke probably also do other healthy things, such as generally having a good diet, going to their doctor when they have worrying symptoms and so on. All of a person’s health seeking behaviours together will contribute to the extension of life seen, not just the four behaviours assessed. Also, a person who does not have these health seeking behaviours will probably also have other factors that may adversely affect lifespan, such as being in a lower socio-economic class. Although the researchers adjusted for this and other potential confounders, it is difficult to adjust fully for known confounders, and there will be other unknown and unmeasured factors that have not been adjusted for.
- People’s behaviours and all of the potential confounding factors were assessed at the start of the study, and these may have changed over the course of the study, and this could have affected results.
- People enrolled in this study were relatively healthy middle-aged adults, with no known heart disease or cancers, representative of people in Norfolk and the results may not apply equally to other populations.
- Although the strong association has been demonstrated in a prospective study, this was not a randomised study and therefore the assumption that if people with four unhealthy behaviours change their lives to eliminate these behaviours, they will live 14 years longer, remains to be tested.
This is a good study, which is one of few to have quantified the combined effects of the four known healthy behaviours. It reinforces a message that is well known: that a good diet and exercise, and not smoking or drinking too much is good for you and may extend your life. However, knowledge is often not enough to change behaviour and commentators have noted the practical difficulties in getting large groups of people to give up unhealthy habits. This research shows that the benefits of policies that achieve this may be large.