Scientists haven't been able to verify it, but there is some evidence to support the idea that milk actually might induce sleep. Milk contains tryptophan, an amino acid, which is the precursor of a brain transmitter, serotonin, which we know has sedative qualities.

But does cow's milk contain enough tryptophan to induce sleepiness?

Representatives of the dairy industry, who might be the first to claim such a benefit for milk, are reluctant to do so and are openly sceptical about its sleep-inducing qualities.

Research indicates it might take a dose as high as 2 litres to provide any sleep benefits.

And with this quantity of milk intake, your bladder might argue with your brain about whether you really want to sleep through the night.

And does warm milk promote sleep any better than cold milk?

It does if you believe it does, but none of the experts could provide a logical reason why it should.