Will Kiwi Fruit Cure Your Insomnia?

A few years ago a popular TV doctor advocated eating kiwi fruit to treat insomnia. Since then I have had many patients ask if this is the answer to their sleep problems. If you want a short answer then I will simply say: If eating kiwi fruit was an effective treatment for insomnia, I wouldn’t have a job. If you want the longer answer – read on.

There is a lot of interest in the role of food in treating sleep problems. When I ask my patients with insomnia what they have tried in order to improve their sleep, almost everyone mentions some dietary change. It could be eating less, or more, at night, eating lettuce, drinking milk or eating turkey breast before bed, or it could be trying various herbal teas. Some people take a more comprehensive approach by giving up meat, cutting out carbohydrates or doing intermittent fasting. Clearly, for the patients that end up coming to my clinic these changes haven’t worked. It is possible that they may work for some people and as a result those people never need to see a sleep doctor. So what does the science say?

Surprisingly, the research on the impact of different foods on sleep is pretty sparse. There is a lack of good scientific data, though there is increasing interest in the field from the scientific community. I will look at some of this research in future blogs, but for now let’s look at what the science says about kiwi fruit and sleep.

Firstly, what is it about kiwi fruit that might make it beneficial for sleep? Kiwis contain, amongst other things, numerous anti-oxidants, serotonin and melatonin. Melatonin is a hormone which, in humans, is secreted at night that helps to synchronise our body clocks and is mildly sedating. As such it helps prepare the body for sleep and melatonin is used as a sleeping pill. So it seems a reasonable question to ask whether fruits high in melatonin might be good for insomnia.

In a 2011 study by Taiwanese researchers they asked subjects to eat two kiwi fruit an hour before bed for four weeks and they found that it reduced the time taken to fall asleep and increased sleep time. However, there was no control group in the study and so it is impossible to know how much of this improvement was due to the placebo effect, or whether the subjects would have improved anyway. So in 2017 a Norwegian team published a similar experiment, but this time they had a control group who ate pears before bed. They found that the kiwi eaters reported better sleep quality and better daytime function than the pear eaters. However, on 10 other measures, including all the objective measures, there was no difference between the groups. So it was encouraging but hardly definitive.

Finally, a 2018 study took a different approach, looking at fruit and vegetable intake in around 14 000 women. They found that eating a portion of kiwi fruit was associated was associated with 10 minutes less sleep a day! It’s probably worth pointing out that this was a statistically significant reduction, but in the real world 10 minutes is probably neither here nor there. They also found reduced sleep times with other fruits and vegetables. The researchers wondered if the reduced sleep time was because the antioxidants in these foods may have repaired some of the damage that would otherwise have to be repaired during sleep. In other words, eating fruit and veg means you may not need as much sleep. The study looked only at sleep time, not sleep quality so it is also possible that they slept less because their sleep quality was better. But we also have to entertain the possibility that some fruit and vegetables, including kiwis, are bad for sleep.

What we’re left with is a very confused picture: there may be some benefit to eating kiwi fruit before bed, or it may make your sleep worse. Either way the effect is pretty small. And even if it was found to improve sleep there is the practical aspect to consider. I like kiwi fruit as much as the next person, but I couldn’t see myself eating two kiwis before bed every night for weeks, months or years! Unless you really love kiwi it would quickly become a chore. There are more effective ways of treating insomnia such as cognitive behaviour therapy for insomnia. This takes a lot of effort at the start but once one is sleeping better good sleep becomes almost effortless and that’s the way it should be – no fruit required!

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