- The energy drain coincides with a period when physical growth slows
- The brain makes its greatest raid on glucose supplies around the age of five
- Study suggests our bodies can’t afford to grow faster during childhood
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Scientists claim to have solved the mystery of why children grow so slowly compared with other mammals – most of their energy is used to expand their brains.
The ‘brain drain’ of energy coincides with the periods of childhood when physical growth slows or stalls, they claim.
Brain scans reveal that a five-year old’s brain is an ‘energy monster’ which uses twice as much glucose – the energy that fuels the brain – as that of a full-grown adult.
The study suggests children grow slower than other mammals because most of their energy is being used to expand their brains
A study from Northwestern University suggests this could be the reason why humans grow at a pace more typical of a reptile than a mammal during childhood.
Christopher Kuzawa, professor of anthropology at Northwestern’s Weinberg College of Arts and Sciences, Illinois, said: ‘Our findings suggest that our bodies can’t afford to grow faster during the toddler and childhood years because a huge quantity of resources is required to fuel the developing human brain.
‘As humans we have so much to learn, and that learning requires a complex and energy-hungry brain.’
Scientists found that the brain makes its largest raid on glucose supplies around the age of five
The study is the first to pool existing PET and MRI brain scan data — which measure glucose uptake and brain volume — to show that the ages when the brain gobbles the most resources are also the ages when body growth is slowest.
At four years of age, when this ‘brain drain’ is at its peak and body growth slows to its minimum, the brain burns through resources at a rate equivalent to 66 per cent of what the entire body uses at rest.
Dr Kuzawa said: ‘After a certain age it becomes difficult to guess a toddler or young child’s age by their size.
‘Instead you have to listen to their speech and watch their behaviour. Our study suggests that this is no accident.
‘Body growth grinds nearly to a halt at the ages when brain development is happening at a lightning pace, because the brain is sapping up the available resources.’
It was previously believed that the brain’s demand for energy was largest at birth, when the size of the brain relative to the body is greatest.
The researchers found instead that the brain makes its largest raid on glucose supplies around the age of five.
Dr Kuzawa said: ‘The mid-childhood peak in brain costs has to do with the fact that synapses, connections in the brain, max out at this age, when we learn so many of the things we need to know to be successful humans.’
Results of the study are published in the journal Proceedings of the National Academy of Sciences.
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