Can popularity be the route to a healthy lifestyle?

Playground games and sports activities during and after school are traditional parts of growing up, and we all remember having fun running, jumping, hopping and skipping around in the first few years of life. It's natural for a young child to want to move around a lot during a normal day, especially when it's with friends at school or home, and parents usually encourage this – up to a point – as regular exercise is healthy.

New evidence suggests that children with more friends tend to have longer periods of physical activity than those with fewer friends, and that if children get into the early habit of exercise, it has long-term benefits for health, and years down the line, can even guard against serious diseases, such as cancer.

In one of the first studies of its kind, researchers at Bristol University found that for each additional friend they have, a child spends around an extra 10 minutes being physically active at the weekend. They also found that having an extra friend was associated with almost four additional minutes of moderate to vigorous physical activity after school – but the link was only observed in girls, not boys, which suggested stronger friendship associations for young girls.

The lack of research on how children participate in physical activities, including sports, and whether having friends influences this, has largely been due to the difficulty of collecting reliable data on children's activity. But with the use of modern technology, researchers were able to attach "actigraph accelerometers" to children, which were worn for seven days and recorded data on vertical motion (such as from jumping up and down or generally moving around). Pupils in Year 6 – aged 10 to 11 – from 23 primary schools in Bristol were chosen to take part in the study, as this is a crucial age for children which affects their future participation in exercise and sport – the transition from primary to secondary school.

In a previous study, the Bristol researchers showed that having "best friends" who are active and engaging in activity with friends outside of school were associated with higher levels of activity among 10- to 11-year-olds. However, it was not clear from this study whether general friend support, friend support for physical activity, or the overall number of friends, influences children's physical activity. In the new study, the researchers wanted to find out whether these friendship factors are linked to change in physical activity after the transition to secondary school, which they describe as "a critical period when children's activity levels decline".

Dr Russell Jago, of the Bristol University's Centre for Exercise, Nutrition and Health Sciences, which carried out the recent research, explains: "The study shows that children are receptive to being encouraged to undertake more physical activity. The higher levels among girls with more friends and having friends who support physical activity suggests that promoting activity with friends could be helpful.

"The age of 10 to 11 is crucial in most children's development, as activity levels – that is, playing games at school, sports and outdoor activities – tend to fall off after they move to secondary school. In the last year at primary school, children are the kings of the castle, as they're the oldest, and then suddenly in secondary school, they're the new kids and the more formal structure means that they are getting less regular exercise, and only as part of a wider curriculum. This tends to be more marked among girls than boys," he adds.

The study, recently published in the US journal Medicine & Science in Sports and Exercise, found that while at primary school, boys took part in around 26 minutes of moderate to vigorous physical activity after school, while girls took part in around 21 minutes, on a daily basis, which is a significant proportion of children's recommended 60 minutes of physical activity a day. At the weekend, boys and girls took part in 45 minutes and 36 minutes a day respectively.

However, there was a 16 per cent decline in boys' after-school moderate to vigorous physical activity in their first year of secondary school, compared with that in primary school, and for girls, this fell by around 12 per cent. At the weekend, the amount for both sexes increased, which researchers believe may be due to less adult supervision of play or sport, but the reasons for the fall in after-school activity is less clear, they say.

Other medical studies have found that getting involved in exercise in early life is crucial for long-term health benefits. Dr Rachel Thompson, deputy head of science at the World Cancer Research Fund, which supported the study, says: "We know that physical activity is an important factor in reducing cancer risk in later life, and it's vital that being physically active is a habit we develop early. This study shows physical activity at below recommended levels for primary school children, with a further drop in after-school activity after the move to secondary school which is particularly concerning. It suggests this transition period is critical for improving physical activity levels among children and understanding the influence of friends is essential."

Dr Jago and his team carried out the latest study as part of the wider Personal and Environmental Associations with Children's Health (PEACH) project, which is looking at all aspects of children's health in the 10-11 age group. In recent years, there has been much media coverage of how children are doing less exercise and becoming more obese. The figures seem to support this view – the 2008 Health Survey for England by the Department of Health found that only 33 per cent of boys and 21 per cent of girls, aged between four and 15, met the Government's recommendations for physical activity of at least 60 minutes a day, seven days a week.

Clearly, there have been social changes that have contributed to the decline. Children in later primary school years are now given more homework than previously, and many go to bigger secondary schools where it may be more difficult to take part in regular after-school activity. There might also be a reluctance by some parents to allow their children to stay later at school, for safety reasons, or because it doesn't fit with the parent's working day.

But one thing seems to emerge strikingly from the research – the important role of friends in how much activity children in the "crossover" group take part in. Dr Cynthia McVey, a child psychologist at Glasgow Caledonian University, says that physical activity plays a great role in the way children socialise in the early years and that the two aspects are interlinked.

"Children who are 'out and about' are more likely to meet other children and because they meet a wide range of children their own age, they're more likely to feel comfortable in social situations, and form friendships more easily," says Dr McVey. "Some schools are better than others at organising after-school activities, such as sports, and see it as more important. Where these aren't available, it's often down the child to find activities to take part in, and we know, for example, that children play in the street a lot less now than earlier generations, forseveral reasons, including parental concerns about letting children play outside for long periods.

"But play is important for developmental reasons, as well as health reasons. Structured play, such as team games and sports, help to develop certain skills, like working as part of a team, and understanding your team-mates strengths and weaknesses. Unstructured play, where there is no adult supervision, helps to develop other talents, such as imagination and role-playing, in games with other children.

"In terms of the difference between boys and girls in spending time on physical activity, this becomes more pronounced after the age of 11 or 12. Boys tend to have role models who are footballers or athletes, whereas girls tend to be more interested in female celebrities, fashion models or singers, and these don't encourage girls to take part in regular physical activity.

"Parents today are also more conscious of risk, in terms of their children's safety, which is necessary, of course, but this can go too far if children are prevented from taking part in physical activity with a small degree of risk – for example, children using climbing frames, ropes and hurdles, as this prevents a child from evaluating risks themselves and having to make their own decisions. When a child reaches the age of seven or eight, they need to able to deal with a certain amount of risk in the outside world, within reason."

Today's parents have a difficult balancing act to perform when it comes to deciding how much activity their child should be having. If children see their friends spending a lot of time playing computer games and watching television or films, they will tend to want to do the same sort of things. Most psychologists agree that if a parent introduces their child to different activities early on, it's more likely that the child will carry on doing one or more of them in later life.

Jenny Butcher, 37, a marketing manager who lives in Berkshire, has three children: six-year-old Evie, five-year old Dylan and Lydia, who is 16 months. She says that both her husband and her are aware of the need to encourage their children to get involved in activities.

"It's something that we've tried to introduce them to early," says Jenny. Dylan takes part in touch rugby and swimming, and he's got to know a much wider range of children than just his classmates, and children a few years older than him, and I think this makes him much more confident in social situations. Evie goes to ballet and tap classes and Rainbows (a pre-Brownies group) and, apart from enjoying all the activities, it's good for her to meet other children from different backgrounds."

Dr Jago hopes his team's findings will allow better long-term strategies to be developed that will encourage girls, in particular, to participate in more regular exercise after they reach secondary school. "Understanding the factors that influence change in youth physical activity is an essential first phase of developing interventions to halt the decline during the transition to secondary school and our findings suggest that fostering activity with friends and friend support for physical activity may be helpful in this process," he says.