Half of all seven-year-olds not exercising enough

Seven-year-olds "risk being couch potatoes of the future," The Guardian warns. The alarming news reports on the findings of a new study that suggests that only around half of UK seven-year-olds meet the daily recommended levels of exercise.

The study in question looked at how much physical activity UK primary school children did and how long they spent sitting (sedentary behaviour).

The research, which involved a sample of around 6,500 children with an average age of 7.5, objectively measured physical activity using an accelerometer (similar to a pedometer) that the children wore for up to a week.

The results appear to confirm fears that young children are spending too much time in front of computer and TV screens and not enough time running around.

This is worrying, as previous studies have found that children who don't exercise enough often have an increased risk of developing a chronic disease, such as heart disease or diabetes, as adults.

It is now up to policymakers, schools and parents to find ways to encourage children to exercise more and, as the researchers put it, build on the legacy of the London 2012 Olympic Games.

Where did the story come from?

The study was carried out by researchers from the Medical Research Council, the University of London, and Bristol Dental School. It was funded by various public bodies, including the Wellcome Trust, the Department of Health National Institute for Health Research, and the Economic and Social Research Council.

The study was published in the peer-reviewed open access journal BMJ Open and the paper is free to read or download.

As might be expected, the story was covered widely in the media, with the Daily Mail referring to "shocking figures" on "couch potato seven-year-olds". On this occasion, the alarming headlines seem to be justified.

What kind of research was this?

This was a large UK cohort study. Researchers wanted to measure primary school children's levels of physical activity, the time they spent sitting and whether they adhered to national physical activity guidelines. It took a snapshot of the physical activity the children engaged in over a week-long period.

The researchers point out that the benefits of physical activity for children and adolescents include weight loss, reduced risk factors for cardiovascular disease, better bone and muscle health, and better psychological wellbeing. Conversely, high levels of "sedentary behaviour" such as TV viewing may result in a higher risk of cardiovascular disease in later life.

The researchers point out that new UK guidelines on physical activity in children published in July 2011 recommend that all young people engage in moderate-to-vigorous intensity physical activity for at least 60 minutes and up to several hours every day. For the first time, it is recommended that extended time spent sitting should be reduced, although a daily limit is not specified.

What did the research involve?

The researchers used data from the Millennium Cohort Study, an ongoing nationally representative study of the social, economic and health-related circumstances of children born in the UK between September 2000 and January 2002.

The original cohort comprised 18,818 children whose parents were first interviewed at home when their child was nine months old. Since then, data has been collected when the children were aged 3, 5 and 7 years, with follow-up currently being conducted at 11 years and planned for 14 years and beyond.

For this study, a total of 14,043 children were interviewed at the age of seven and invited to have their physical activity levels monitored. Those who consented were sent an accelerometer, a small device worn on an elasticated belt to measure physical activity levels by assessing how quickly the device is accelerating.

The children were asked to wear it during waking hours for a week and to only take it off when they bathed, swam or went to bed. The device was set to record activity as counts per minute (cpm) and steps.

Data was collected between May 2008 and August 2009. Accelerometers were returned by 9,772 children. Only those who wore the gadget for 10 hours or more on at least two days were included in the study, resulting in a final sample of 6,497 children (3,176 boys and 3,321 girls) with a total of 36,309 days (nearly 449,000 hours).

For each child, researchers calculated:

• total physical activity (average cpm) over the period worn
• average number of daily steps and minutes of sedentary time (defined as less than 100 cpm) and moderate-to-vigorous intensity physical activity (more than 2,241 cpm)

In their statistical analysis, they also looked at other potential confounders collected in the interview, including gender, age, ethnicity, maternal occupation, family structure and country and region of residence.

What were the basic results?

The analysis showed that on average, children spent 60 minutes a day on moderately vigorous physical activity and took an average of 10,229 daily steps. However:

• only 51% of the children achieved the current recommendation of 60 minutes of moderate-to-vigorous physical activity every day
• 38% of girls achieved this compared with almost two-thirds of the boys (63%), and in general girls fared worse than boys in terms of total daily physical activity
• children in Northern Ireland were the least active, with 43% managing 60 minutes of moderate-to-vigorous physical activity every day
• children in Scotland were most likely (52.5%) to achieve the minimum daily target
• in England, children living in the northwest (58%) were most likely to achieve the target, while children in the midlands (46%) were least likely to do so
• half (50%) of the children were sedentary for 6.4 hours or more a day

Other findings included:

• Children whose mothers have never worked or had been long-term unemployed were the most likely to meet the recommended levels of daily physical activity and had the lowest average daily hours of sedentary behaviour.
• Children from two-parent families engaged in less total physical activity and daily moderately vigorous physical activity than those whose mothers did not live with partners. These children also took the least steps and were least likely to meet the moderately vigorous physical activity recommendation.
• Overall, activity levels were lowest in children of Indian origin, with 33% of children of Bangladeshi origin meeting the recommended daily exercise minimum.

How did the researchers interpret the results?

The researchers say a "comprehensive policy response" is needed to boost physical activity and reduce sedentary time among all young children.

In an accompanying podcast, senior author Professor Carol Dezateux describes the gender differences in exercise levels as "striking" and calls for policies to promote more exercise among girls, including dancing, playground activities and ball games.

The authors refer to the legacy of the London 2012 Olympic Games, which promised to inspire a generation to take part in sport: "The results of our study… strongly suggest that contemporary UK children are insufficiently active, implying that effort is needed to boost [physical activity] among young people to the level appropriate for good health."

This is likely to require population-wide interventions, they say, including policies to make it easier for kids to walk to school, in a bid to increase physical activity and curb the amount of time they are sedentary.

"Investing in this area is a vital component to deliver the Olympic legacy and improve the short- and long-term health of our children," they conclude.

Conclusion

This was a large, well-conducted UK-wide study of a sample of around 6,500 seven-year-old children that objectively measured their physical activity and sedentary time. Accelerometers provide more accurate measures of physical activity than self-reporting.

The results are also likely to give a fairly reliable indication of the children's normal activity levels, as young children are less likely than adults to moderate their activity because they are aware that their activity is being monitored.

Although, as the authors note, accelerometers can underestimate physical activities as a result of the position they are worn in, or their removal during water-based activity or contact sports.

It is also worth pointing out that much of the time these children spent sitting was probably spent in school lessons rather than in front of a TV screen.

There are, however, further limitations to the study. Of around 14,000 children asked to participate in the accelerometer study, only around half agreed to do so and were sufficiently compliant with wearing the device for their results to be analysed.

Therefore, although the sample of children in the cohort is a representative population sample, it is possible that the activity levels from the half that participated could differ from the half who did not.

Some observations – such as that activity levels were greater among children whose mothers didn't work or children of minority ethnic groups were less active – were based on small sample sizes.

This means these findings may not be as accurate. For example, average activity levels among white children are taken from a sample size of 5,710, while average activity levels for Bangladeshi children come from a sample size of only 70.  No assumptions should be made from these observations, therefore, as they may be less reliable and may not be statistically significant.

Despite these limitations, the study makes for alarming reading and will be of concern to parents and policymakers alike. The UK's Chief Medical Officers' current guidelines advise that children and young people between the ages of 5 and 18 engage in moderate-to-vigorous physical activity for at least one to several hours daily.