Could lack of sleep be a cause of childhood obesity?
REDUCED sleep has been linked to excessive weight gain in children, but the relationship between sleep and diet remains unclear.
Many culprits have been blamed for the alarming rise in childhood obesity in recent years. Video games. Fast food. Portion sizes. Television and computer screens. A decline in home cooking. The vanishing of school playing-fields.
Here's another worry to throw into the mix: sleep. An eye-opening study from New Zealand was published in the British Medical Journal earlier this year. Researchers studied 244 children, following them from the age of three to seven.
They found that reduced sleep significantly increased the likelihood of excessive weight gain. The children who slept longer aged three to five were 61 per cent less likely to be overweight aged seven.
'But wait!' you say. 'I bet the households where children slept less were neglectful and poor. Probably they watched more television and ate a bad diet, too.' Well, actually, no. One of the things that makes this study so striking is that the researchers took account of many 'confounders' such as household income, fruit and vegetable intake, television watching and the mother's education.
The link between lack of sleep and increased obesity held good even when all these variables were allowed for. Each additional hour of sleep aged three to five reduced the BMI (body mass index) at the age of seven by 0.49.
This is small, but multiplied over several years, it could make the difference between being obese and not – something life-changing to the child. (You can read the full report at bmj.com; search for 'flame study')
Why would not getting enough sleep make a child fat? For one thing, less sleep means more waking hours in which to eat. It also means greater tiredness during the day, which may cause you to be less active. There are suggestions, too, that sleep deprivation triggers a hormonal response, sending the appetite haywire. I know that if I haven't slept well I fall on my breakfast toast like a vampire.
Not enough is really known about the mysterious relationship between sleep and diet. It certainly doesn't all go one way. If I think of the adults I know who suffer insomnia, many are notably slender, maybe because tossing and turning uses up more calories than sleeping peacefully.
The great French philosopher of food Brillat-Savarin was convinced that sleeping too much was one of the causes of obesity. 'A hungry man cannot sleep, for the pain he suffers keeps him awake.'
We can all think of meals that send us to sleep better than others. Dark chocolate is clearly stimulating, because of the caffeine. I find that chillis and lime juice wake me up, too, whereas a dish of creamy pasta or risotto feels like a recipe for instant snoring: not great for a working lunch, but soothing on a cold evening when you want an early night.
And anyone who has read The Tale of the Flopsy Bunnies by Beatrix Potter knows that too much lettuce is soporific. It turns
out that there really is a substance in some species of lettuce called lactucarium or 'lettuce opium', which does act as a mild sedative. Perhaps, like little bunnies, we should feed our infants lettuce before bed.
Food and sleep are two of the great universals of human existence. To be alive in the West right now is to be exposed to too much of one and not enough of the other. It would be surprising if there weren't some kind of connection.