Will a cup of warm milk at bedtime entice the Sandman your way?
Research suggests there’s a link between food and sleep, say the authors of a comprehensive review of the effects of diet on sleep length and quality,* and milk is rich in tryptophan, an amino acid important to sleep.
Tryptophan is a precursor to melatonin, the hormone of darkness. Your body begins secreting melatonin a few hours before bedtime, helping you fall asleep and sleep through the night. Tryptophan is also a precursor to serotonin, a neurotransmitter which, in addition to promoting alertness, gets converted into melatonin.
Foods high in tryptophan include
- Meat, fish, seafood and egg whites
- Cheese, milk and yogurt
- Pumpkin and sunflower seeds, cashews, almonds and walnuts
- Beans, split peas, peanuts and lentils.
The Devil in the Details
But tryptophan has to cross the blood-brain barrier to exert its sleep-inducing effects. It competes with other amino acids to cross that barrier, so a bedtime snack high in tryptophan alone may not yield much bang for the buck.
One way to ensure that lots of dietary tryptophan DOES get across the blood-brain barrier is to have a snack that combines a tryptophan-rich food with a carbohydrate:
- Milk and cereal
- Beans and rice
- A turkey sandwich
- Hummus on pita bread.
Eating the carbohydrate promotes the release of insulin, which inhibits the production of competing amino acids or diverts them into muscle. With less competition at the gate, more tryptophan gets across the blood-brain barrier. It then begins its conversion into serotonin and melatonin, in turn promoting sleep.
Nutritional deficiencies in the group B vitamins and magnesium have been found to impair sleep, say the authors of the review. A sleep-friendly diet will include foods high in tryptophan and unrefined carbohydrates, as well as group B vitamins and magnesium.