What is the link between nutrition and sleep? How does what we eat impact our quality of sleep?

We asked Accredited Practising Dietitian, Caitlin, for her insights on this topic recently. Here's what she shared.

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Timing of your last meal and bed

I often hear people worrying about eating too close to bedtime. Generally speaking, there is no amount of time you have to wait after having dinner before going to bed. Depending on the meal you ate, it can take up to 6-8 hours for food to pass through your stomach and small intestine. Your digestive system continues to work while you sleep. The exception to this would be if you have any issue with gastric reflux (GORD) or heart burn. If this is the case, it's generally recommended to wait at least 2-3 hours before lying down after eating food.

Caffeine

Too much caffeine too close to bed may be disruptive to sleep. Caffeine is a stimulant, so this can make it harder to fall asleep.

The half-life of caffeine (the time it takes for a quantity of a substance to reduce by half the original amount) is about 5 hours. So, if you have an instant coffee (~100mg caffeine) you will still have 50mg of caffeine in your body after 5 hours.

The Sleep Health Foundation (Australia) recommend avoiding caffeine at least 3-7 hours before sleep, or even longer if you are sensitive to caffeine.

Food Standards Australia New Zealand (FSANZ) recommend:

• No more than 400mg caffeine per day, and no more than 200mg in a single sitting for adults
• No more than 3mg caffeine per kilo for children
• No more than 200mg caffeine per day for women who are pregnant and/or breastfeeding

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Melatonin

Melatonin is a hormone that is secreted by your pineal gland. It plays a big role in your circadian rhythm (24 hour body clock), by helping us fall asleep. Generally, melatonin is produced in response to dark so light can suppress melatonin synthesis. As levels of melatonin increase, you begin to feel sleepy.

Melatonin is sold as a supplement, which is thought to help us regulate our sleep, particularly for people who work shift work. The evidence as to whether they work or not is a bit mixed, and perhaps some of that is because there seems that the dose is not a one-size-fits-all approach. Supplements come in a variety of doses and some people seem to need more than others to get a benefit (if they get any benefit at all).

Magnesium

Magnesium is an essential mineral that has many roles in our body. It is found in leafy green vegetables, nuts & seeds, wholegrains, soy products and dairy foods.

Magnesium is hypothesised to be helpful in regulating the sleep-wake cycle due to its role as an electrolyte and co-factor. More research needs to be done to determine whether a supplement would provide the suggested benefits. There is some evidence that it may help to decrease the time it takes to fall asleep, improve the quality of sleep and help people who have sleep related movement disorders (e.g. restless leg syndrome), but the evidence is mixed.

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