Three hours of uninterrupted sitting may cause substantial disruption to vascular function in the legs in young girls, suggests a study published in Experimental Physiology.

The researchers used an experiment which involved 7-10 year old girls completing two 3-hour periods of sitting. One of these was uninterrupted and the girls sat for the entire three hours. The other was interrupted once an hour with a 10 minute moderate intensity exercise break. They assessed the health of the main artery in the leg before and after each of the 3-hour periods of sitting. Healthy artery function requires a balance in the dilation (enlargement) and constriction (narrowing) of the artery diameter, which helps to regulate blood flow. Uninterrupted sitting for 3 hours caused a 33% reduction in the ability of the artery to dilate (enlarge). A 10-minute exercise break, however, was able to prevent this adverse impact of uninterrupted sitting.

Prolonged periods of sitting can have a detrimental impact on blood vessels and has previously been shown to even change the anatomy of limb arteries in adults and leads to increased cardiovascular disease risk. Dr Ali McManus, Centre for Heart, Lung and Vascular Health at the University of British Columbia and lead author of the study commented,

'A sedentary lifestyle (excessive sitting) poses a huge health concern for adults and - as our study has shown - also for children. Only 7% of Canadian children now attain the recommended one-hour per day of moderate to vigorous physical activity and are spending up to 5 hours per day sitting.

'Inactive children later become inactive adults. Inactivity is the fourth major risk factor for global mortality, contributing to 3.2 million deaths annually. Every parent should be asking 'is the amount of time my child spends sitting harmful?'

She adds, 'Our study has shown that three hours of uninterrupted sitting is harmful. We have also shown that interrupting sitting with regular exercise breaks prevents the negative health impact from too much sitting. A modest 10% reduction in sedentary behaviour has the potential to reduce direct health care costs by $150 million a year in Canada.'

'Limiting the amount of time we spend sitting will not only result in lower health care costs and a larger and more productive workforce, but also in a reduced death and disability rate. This in turn will boost productivity and increase GDP and builds a strong case for action.

'We only studied girls in this experiment. Future work will include boys and children who are at higher risk for excessive sitting. We will also explore whether the sitting induced reductions in leg blood flow are accompanied by altered brain blood flow and cognitive function. In the longer-term we will develop 'inactivity' surveillance and intervention tools for identifying children 'at sedentary health risk' and preventing excessive sitting.'