Asked by: Thomas Mitchell, Chelmsford

Warm milk may be soothing, but the jury is out on its soporific qualities. Milk contains a protein called alpha-lactalbumin, a source of the amino acid tryptophan. This forms serotonin, a neurotransmitter that helps to regulate mood and sleep. Consuming alpha-lactalbumin increases blood levels of tryptophan.

However, research shows that a large dose is required to give enough tryptophan for the desired effect. Milk also contains a bioactive peptide, casein hydrolysate, which is thought to have anti-stress properties, while magnesium could help with restless legs.

A Dutch trial on 15 women with insomnia suggests that milk may improve sleep, especially when enriched with magnesium and the protein casein hydrolysate.

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Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.