Newsletter #265: Can Eating Kiwis Enhance Your Sleep? 🥝
As we’ve discussed here before, it’s well established that insufficient sleep drives changes in our eating habits. For example, we tend to eat more, without altering our energy expenditure to compensate, and we are more likely to gravitate toward energy-dense foods that promote weight gain.
Far less is known about the impact of our food choices on sleep. However, a couple of trials have been published recently that found that eating kiwifruit was surprisingly beneficial. Among other improvements, eating two kiwifruit led to these participants getting close to an extra hour of sleep, which is something that most of us would welcome.
Now, before I get into the details, I would be remiss if I did not point out that these studies should probably be taken with a sizable grain of salt. For one thing, these are open-label trials without a control group, which makes it hard to tell if these improvements might be due to placebo effects, especially in the case of people who are already battling sleep issues and are probably anxious to find something to ameliorate their woes. Secondly, some of the underlying mechanisms proposed by researchers to explain these results either aren’t truly specific to kiwifruit, or they just don’t make a ton of sense. For example, it was suggested that kiwifruit may enhance sleep through high levels of naturally occurring serotonin in the fruit. But as far as I can tell, serotonin consumed in food cannot cross the blood-brain barrier.
That having been said, there is at least one biologically plausible explanation for these findings that comes to mind (maybe). Kiwifruit really do stand out, among all fruits, in their antioxidant content. Two kiwifruit (130 g, the amount tested in these trials) contains around 161% of the Daily Value for vitamin C, as well as 11% of the Daily Value for vitamin E. This is a higher proportion of vitamin C than even citrus, or any other commonly consumed fruit for that matter. And we know from a randomized trial that consuming kiwifruit results in significant increases in antioxidant status and protection against oxidative DNA damage. Could this help with sleep? Perhaps. A systematic review of observational studies found that higher dietary antioxidant capacity was linked to lower likelihood of poor sleep.
That having been said, I can’t see the harm in trying it, and as you’ll see, the apparent impact of the fruit is pretty damn impressive. 👇
This Week’s Research Highlights
🥝 In individuals reporting sleep problems, eating two kiwifruits before bed led to substantial improvements in sleep duration and quality.
Researchers at Taipei Medical University received funding from Zespri Kiwifruit to examine how the fruit could affect aspects of sleep (for better and for worse, this is the typical origin story for a lot of nutrition studies). To that end, they recruited 24 subjects, all of whom reported some form of sleep disturbance. For three days, participants filled out standardized questionnaires on their sleep quality and maintained a sleep diary so that the researchers could see what their sleep looked like at baseline. The subjects' sleep was also objectively measured using actigraphs — small wrist-worn sensors, kind of like Fitbits, that continuously collect data on movement and various aspects of sleep. Then, for four weeks, the participants were directed to eat two kiwifruits, one hour before bed, every night, while they continued to record data on their sleep. After four weeks of data collection, substantial improvements in sleep were evident. First of all, actigraphy showed that they fell asleep nearly seven minutes faster, and their sleep was more efficient, meaning that they spent less time awake while they were in bed. They also got significantly more sleep. Based on actigraphy, their total sleep time increased on average by 55 minutes. Finally, they seemed to sleep better. Their scores on the sleep quality questionnaire dropped by more than 42% (in the inventory they were using, higher score = worse quality). For a food-based — as opposed to pharmaceutical — intervention, these improvements in sleep are massive.
Previous research has shown that elite athletes, for various reasons, report poorer sleep quality versus non-athlete controls. Notably, although total sleep duration tends to be fairly similar, objective measurements show that athletes experience worse sleep efficiency. To examine whether kiwifruit could enhance sleep in this population, researchers in Ireland recruited a total of 15 elite athletes from a national sailing squad as well as a national squad of middle distance runners. The participants underwent a questionnaire battery, as well as a detailed daily sleep diary for one control week to establish baseline sleep characteristics. Then, for four weeks, they ate two green kiwifruit nightly, one hour before bed (just like the Taiwanese study described above). During this time, they continued to keep records of their sleep. After the 4-week kiwifruit intervention, there were clinically significant improvements in sleep quality, based on their responses to the Pittsburgh Sleep Quality Index (PSQI). Their PSQI global scores dropped from a baseline of 6.47 ± 2.17 down to 4.13 ± 1.19 after the kiwifruit intervention. To put that into perspective, a score of 0–4 is said to indicate "good sleep," while anything above 5 denotes "poor sleep." So their sleep quality had moved from the unhealthy to the healthy range, which is pretty good. But perhaps even more impressively, their total sleep time increased by an hour (from 7 hours and 36 min to 8 hours and 38 min). We know from prior research that extending sleep by an hour can significantly improve athletic performance. For instance, when members of the Stanford NCAA basketball team were instructed by researchers to sleep longer, their shooting accuracy improved, with free throw percentage increasing by 9% and 3-point field goal percentage increasing by 9.2%, and all participants were faster, shaving nearly a second off of their sprint time. So more sleep is not just good for your health, it can boost your physical performance in measurable and meaningful ways.
Random Trivia & Weird News
If you've spent any time on Reddit, you've no doubt seen the assertion, usually backed by various pictures and memes, that "cats are liquid."
Liquid, as a state of matter, is defined as "a nearly incompressible fluid that conforms to the shape of its container...but retains a nearly constant volume independent of pressure."
So, to use a super simple example, if you place an apple into a bowl, it will retain its shape. But if you pour apple juice into the bowl, the juice will modify its form to fit within the container. In this case, the distinction between solid and liquid is fairly clear.
But what about a cat? 🤔
Marc-Antoine Fardin, a physicist at Université Paris Diderot, won the 2017 Ig Nobel Prize in Physics for his publication in the Rheology Bulletin, in which he attempts to answer the surprisingly elusive question of whether cats can be characterized as liquid. He examines photographs of cats in jars, baskets, bowls, and other containers, and concludes that cats exhibit properties of both solid and liquid, and can be either depending upon circumstances.
Podcasts We Loved This Week
- Tommy Wood: Cognitive decline, neurodegeneration, and head injuries — mitigation and prevention strategies, supplements, and more. Via The Drive.
- Stephen Buchmann: Bees have feelings, too. Via Science Friday.
Products We Are Enjoying
Supplemental melatonin can help a lot with falling asleep at the right time, and realigning your circadian rhythm. But it’s important to source melatonin carefully, because quality control for over-the-counter supplements can be really questionable. And this seems to be especially the case for melatonin gummies. You may have heard about a recent chemical analysis of the melatonin gummies, in which they found that almost all brands failed to match the claims on the labels. The actual per-serving dose of melatonin ranged anywhere from 74% to 347% of the labels’ stated amount. That’s why you want to make sure to get a supplement that is independently lab-tested, like Nature Made. As an added bonus, this brand is super easy to find in grocery stores and drug stores all over.
humanOS Catalog Feature of the Week
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Kiwis might facilitate good sleep. But if you really want to optimize your sleep and your circadian rhythms, proper light exposure is going to be your best bet.
We evolved in the presence of natural daily cycles of light and darkness. But obviously, the invention of artificial lighting means that we can now fully control when and how much light we’re exposed to, which has altered this relationship.
Today, most of us spend the majority of the day indoors, under comparatively dim artificial lights. Then, after sundown, we are exposed to more bright light, and importantly more blue light due to our digital devices. Consequently, we are getting less bright light during the day and less darkness at night.
This is key because light sends crucial signals to the body, and the intensity and timing of this light matters for both your health and your performance. But fortunately, there is a lot you can do about it. In this guide, we discuss how you can achieve a pattern of natural light and darkness in the modern world by adjusting behavior, modifying your indoor spaces, configuring your devices, and more.