A new study by UBC Okanagan researchers explores for the first time how sitting affects blood flow in children’s brains.
The School of Health and Exercise Sciences researchers wanted to determine how prolonged sitting impacts the blood flow to children’s brains and how exercise breaks can make a difference. Previous studies have been done on adults, but not a group of children.
“The young brain demands more energy than the adult brain,” says Dr. Christine Tallon, who led the study for her doctoral research under the supervision of Dr. Ali McManus. “This higher demand means a correspondingly higher level of blood flow to the brain. We are therefore quite concerned that prolonged sitting may be worse for children than for adults.”
To assess the impact of extended sitting, a group of children, aged seven to 13, visited a UBCO lab twice. On one visit, they sat for three hours straight. On a separate visit, they again sat for three hours but with a 10-minute exercise break—riding a stationary bike—each hour. For each visit, the researchers performed tests and measured blood flow in the brain using ultrasound.
“One test, called a neurovascular coupling task, looks at how blood flow increases when an area of the brain is engaged in a specific job,” says Dr. Tallon. “In essence, the act of thinking requires a quick, targeted hit of oxygen and nutrients, delivered by the blood.”
For this first test, the children were asked to solve a visual puzzle: looking for a Where’s Waldo character in an illustration. Visual stimulation is known to activate the occipital cortex which leads to a 20 to 30 per cent surge in blood velocity through the artery supplying it. However, the researchers found that with or without exercise breaks, the blood velocity remained unchanged. Dr. Tallon offers an explanation:
“As you might imagine, for children to stay seated for three hours presents a challenge. We allowed them to play games on electronic devices to keep them occupied and this likely impacted the test as the visual cortex would have been steadily engaged.”
This raises the question: if the brain is busy with a thinking task, is prolonged sitting actually a problem?
And this is where the second test comes in. Called cerebrovascular reactivity, this test did show an impact from excessive sitting.
Cerebrovascular reactivity is the ability of the brain’s blood vessels to dilate in response to stimuli—such as an excess of carbon dioxide in the blood—in order to increase blood supply.
A decline in cerebrovascular reactivity has been linked to a cognitive decline in adults.
To test cerebrovascular reactivity, the children were asked before and after the sitting period to breathe in a controlled mixture of air that included a higher than normal—yet still safe—concentration of carbon dioxide. This extra dose of carbon dioxide triggers the dilation of their brains’ blood vessels.
“After sitting for three hours without exercise breaks, the children’s cerebrovascular reactivity had decreased,” says Dr. Tallon. “In other words, the blood vessels had become sluggish.”
However, when exercise breaks were added, the children showed no sign of reduced cerebrovascular reactivity. Their blood vessels dilated at the same rate as prior to the test.
So, what does this mean for parents, teachers and caregivers who may have concerns about children being inactive for prolonged periods?
“Exercise is clearly beneficial and this is exciting,” says Dr. Tallon. “We did 10 minutes of exercise on the hour, but more research can help us identify the optimal dose of exercise to offset any effects of excessive sitting. We can safely say that having kids get up and move at least for a few minutes each hour is going to be good for them.”
The research was published in a recent edition of Experimental Physiology.