From Coffee to Camomile: How Drinks Affect Sleep

Do you avoid drinking coffee after lunchtime so that it doesn’t stop you sleeping? Do you follow your mum’s advice and enjoy a warm, milky drink to help you get to sleep? Let’s look at what the evidence suggests about how non-alcoholic drinks affect sleep.

Caffeine: the world’s favourite stimulant

Tea and coffee contain caffeine, which is “the most widely consumed psychoactive substance in the world”⁽¹⁾. Caffeine blocks adenosine, the chemical that makes you feel sleepy⁽²⁾.  Unlike most stimulants, caffeine is also socially acceptable. Indeed, given the disparaging looks I have experienced when asking for a decaffeinated brew, caffeine can feel socially required! 

Caffeine and sleep

The detrimental effect of caffeine on sleep is well established. It can certainly prolong the time required to fall asleep. However, even if you’re lucky enough to fall asleep, caffeine can reduce total sleep time, impact sleep efficiency, reduce time in deep sleep, and worsen your perception of sleep quality, perhaps due to increased night-time awakenings⁽¹⁾. Of course, a poor night’s sleep can result in you reaching for more caffeinated drinks the next day, which can kick off a vicious cycle.  

How much caffeine is safe?

The NHS suggests the safe daily amount for adults is up to 400mg per day. Pregnant women are advised to consume less than 200mg per day and recommendations for children depend on body weight. As a rough guide, the average mug of coffee contains about 100mg of caffeine, but some brewed coffee can be considerably more. So, the NHS guideline for ‘moderate intake’ is around 2-3 mugs per day.

Remember, other drinks contain caffeine too. The classic British cuppa contains around 50mg of caffeine and can be significantly more if the tea is brewed for a decent amount of time, like it is in Yorkshire! Green tea and matcha also contain caffeine. It’s not just hot drinks either, iced coffee contains caffeine and sugary beverages such as cola are caffeinated, usually around 35mg per can. Interestingly, diet cola often contains more caffeine than the sugary version. Energy drinks are now extremely popular, especially with younger people, and servings contain between 80mg and a whopping 300mg+ of caffeine⁽³⁾.

The half-life of caffeine is around 5-7 hours but can be longer in some people⁽⁴⁾. One study found important disruptive effects on sleep when caffeine was consumed both 3 and 6 hours before bedtime⁽⁵⁾. Another study found that caffeine taken at 7am directly affects sleep propensity as late as 11pm!⁽⁶⁾

Individual differences

Caffeine metabolism is affected by many factors, including genetics⁽⁷⁾, hormones⁽⁸⁾, tolerance⁽⁹⁾, medication⁽¹⁰⁾ and age⁽¹¹⁾. It is therefore highly individualised: “The sleep of older adults may be more sensitive to caffeine compared to younger adults. Pronounced individual differences are also present in young people.”⁽¹⁾

If you have difficulty sleeping, it may be wise to reduce the number of caffeinated drinks you consume and experiment with enjoying caffeine mainly in the morning, to ensure your night-time sleep is not disrupted. It may be a case of ‘trial and error’ to find out what works for you.

Herbal teas and warm milk

If you want to reduce or avoid caffeine, there are a great many alternative drinks to enjoy,  such as herbal teas and warm milky drinks. Could some of these caffeine-free options also be positively beneficial for sleep? 

Camomile and passionflower herbal teas are traditional sleep aids. In a systematic review and meta-analysis, camomile herbal tea was not found to be associated with a significant change in insomnia severity, however, a significant improvement in overall sleep quality was found⁽¹²⁾. Short-term sleep benefits of passionflower herbal tea were reported in one study⁽¹³⁾, however it was a small sample size. Further research is needed into beneficial effect of herbal teas. 

There is some limited evidence that milky drinks are associated with improved sleep quality,  in both children and adults⁽¹⁴⁾. This may be because milk is a good dietary source of tryptophan which helps your body make the ‘sleep hormones’ melatonin and serotonin.  Carbohydrate also has been linked with falling asleep more quickly in healthy sleepers,  perhaps because carbohydrate increases the uptake of tryptophan in the brain⁽¹⁵⁾. This could explain why traditional sweetened, malted drinks may feel so soothing, although this requires further research. Beware of hot chocolate though, as this usually contains some caffeine! 

If consuming these caffeine-free drinks fits with your dietary preferences and goals, there’s no harm in experimenting with what settles you. You could use a ‘food and sleep diary’ in which you take note of which drinks you consumed and when, and record your sleep onset, sleep quantity and sleep quality, to see whether any patterns emerge.

Take-to-bed message

Small changes in what you drink throughout the whole day may improve your sleep quality and quantity. Sleep is not only about how you end the day, but also about what you sip along the way.

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References

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