Only half of all seven-year-olds in the UK are getting enough exercise each day to stay healthy, a new study has found.

The research, published in BMJ Open, found that half of UK 7-year-olds are sedentary for six to seven hours a day, with girls, children of Indian ethnic origin, and those living in Northern Ireland being the least physically active.

UK guidelines on daily physical activity recommend that children spend at least an hour a day in moderate to vigorous activity and spend less time sitting down.  

The findings are based on a sample of almost 7,000 UK primary school children who were part of the Millennium Cohort Study looking at the health of around 19,000 children born in the UK between 2000 and 2002.

Levels of activity were monitored by fitting the children for seven days with an accelerometer that was only removed during bathing and sleeping.

The researchers at University College London found that only 51% of children achieved the recommended 60 minutes of exercise.

Girls were far less active than boys, with only 38% satisfying the guidelines, compared to 63% of boys.

Lead researcher Carol Dezateux, from University College London's Institute of Child Health, said the difference in levels of activity between girls and boys was "striking".

"Girls were simply much less active than boys," she said. "There are big gender differences around playground times in the school day and we need to understand how to get girls more into ball games playground activities and to offer them physical activities like dancing that may be more attractive to them as well as providing them with adequate role models."

The study's authors warn that more investment and "wide interventions" are needed to encourage the UK's children to be more active.

"The results of our study provide a useful baseline and 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," they wrote.