Ask the experts: Diet and sleep

Senior nutritionist Rose Carr finds out how diet can influence the quality of our sleep.

Q: I sleep for eight hours but I still feel tired when I wake in the morning? Why?

A: Sleep quality can be affected by what we're eating and drinking during the day, especially in the hours before we go to bed. An overfull stomach can cause discomfort while an empty stomach may cause hunger pangs, all of which can stop you falling asleep.

Caffeine is a stimulant and although our susceptibility to it varies, most people will find a coffee before bedtime will increase the time it takes to fall asleep. Dr Alex Bartle, founder of the Sleep Well Clinic, puts it in context by comparing a 'No-doze' tablet, which contains 100mg of caffeine and is designed to keep us alert, to one teaspoon of instant coffee at around 80mg, a strong cup of tea at 50mg or a double-shot espresso at 110-120mg. "The effects of caffeine are cumulative and they last for five to eight hours," says Dr Bartle. His advice? "If you have trouble sleeping, avoid caffeine after 2pm." Remember, caffeine is also found in chocolate, chocolate drinks, cola and energy drinks.

Dr Bartle highlights the dual role alcohol can play, saying, "Generally a large glass of wine (or two units of alcohol) before bed is sedating but anything more has the opposite effect as the breakdown products of alcohol disturb the quality of our sleep and can cause us to wake in the night."

Q: Is there a link between being overweight and sleep?

Research has found sleep duration of less than six hours a night is associated with weight-gain and obesity, both in adults and children. It seems shorter sleeps alter levels of the hormones ghrelin and leptin, which control hunger and appetite, and thus promote overeating.

If you already carry excess weight your breathing can become laboured or disrupted during sleep, as excess weight can limit space for the diaphragm to expand and cause a narrowing of upper airways. Snoring is a common symptom. While alcohol will exacerbate the problem, the good news is that losing weight can significantly improve the quality of your sleep (and your partner's).

Q: Some people say milk before bedtime can help you sleep. Is that true?

Often a glass of warm milk with a teaspoon of honey is recommended as a night-time tonic to aid sleep. The theory is milk contains tryptophan, a component of the neurotransmitter serotonin which is important in the control of sleep, and the carbohydrate (from the honey) helps transport the tryptophan to the brain. While the theory makes sense, Dr Bartle points out there is very little tryptophan in milk and it's more likely to work psychologically than physiologically. A warm, soothing drink at bedtime can have a calming effect, which can be very important to sleep. However, beware of chocolate drinks, which will contain caffeine.

Did you know? Regular exercise helps promote sound sleep: it releases tension and helps the body relax.