Introduction

Sleep is known as a state where we are unresponsive and unaware of our environment or surroundings (Source: Elsevier). It is not fully understood why we need sleep, and the fact that our brains are quite active for a large majority of it, further perplexes researchers in the area. OK, we need it to regenerate, so why won’t our brains use this time too? Alongside the increasing research into the behavioural strategies that can improve sleep, there are emerging inquiries into both nutritional strategies as well as supplements. This research is very much preliminary and mechanistic, so caution should be practiced. Nonetheless, if there are rationale pathways by which nutrition can enhance sleep, shouldn’t we emplore them?

In this article you will learn: 

• A brief biology of how we sleep
• How nutrition may be linked with sleep
• Practical ways to avail of this link
• How to improve your sleep

Why look at nutrition for sleep?

Before diving in, I want to highlight that we will not be covering the entirety of this systematic review by Halson today. This esteemed author covered a variety of not only nutritional, but behavioral and environmental factors pertaining to sleep, but let’s stick to the nutrition for now!

So, now you ask, why is nutrition even considered in the same conversation as sleep? You may wonder why a purely behavioural and hormonal action could be linked with our the foods we eat. But they are connected, and in fact, your nutritional habits may play a more prominent role than you think!

The rationale behind this hypothesis is that the main mechanisms of sleep rely on melatonin production, which is dependent on serotonin production which is dependent on tryptophan levels. Tryptophan is the least abundant amino acid we consume in our food, and so by increasing the content of this in the body, we may be able to enhance our sleep hormone. But let’s dive in and see if that is truly possible!

How Sleep Works

The role of melatonin

Like any great researcher, Halson provides a mechanistic rationale that underly the growing interest around nutritional intake and sleep quality. She illuminates the tryptophan - serotonin - melatonin cycle, which is dependent on not only tryptophan intake, but the levels of other competing amino acids in the blood. Simply put, tryptophan is an amino acid that shares the same transporters as other large, neutral amino acids. Therefore, both the amount of tryptophan we consume, as well as the amount of these amino acids accompanying it can impact how much tryptophan reaches our brain. It is here that it will be converted to serotonin and subsequently to melatonin.

Melatonin of course, is known as our sleep hormone. The author briefly highlights that it is released from the pineal gland in the brain, and reacts to messages sent from our eyes, of the amount of light in our immediate surroundings. When it is bright, melatonin production is suppressed which increases the activity of arousal centres in the brain. When it is dark, melatonin is ramped up and acts on these arousal centers, dwindling down activity.

Thus, from this well-elucidated information, the author decided to explore some of main studies that invested dietary strategies of increasing Trp influx into the brain. Well, actually, many of these studies did not necessarily examine Trp concentrations, but they did assess markers of sleep quality and duration.

Dietary Strategies for Improving Sleep

Carbohydrate Intake

Remember, tryptophan competes with other neutral amino acids for transporters that can carry it into the blood and to the brain. Based on this, the author mentions that high carbohydrate meals and diets can stimulate the uptake of these large amino acids by our muscles through the action of insulin (Source: NCBI).

The author highlighted one study that showed improved rapid-eye movement (REM) sleep and decreased light sleep (early, less restorative stages of sleep) and wakefulness after a highcarbohydrate meal (130g) compared to a lowcarbohydrate meal (45g) and no meal, 45 minutes before bed. However, the study only included six participants and did not control calorie intake (Source: NCBI).

The author goes on to highlight several studies that examined different carbohydrate feeding protocols within 1-4 hours of bedtime. They also assessed the different impacts of glycemic index of these meals, as this can largely determine the magnitude of the insulin response e.g. high-GI will cause a greater spike in insulin production. The findings of these studies were mixed, in most part, because low-carb and high-carb meals impacted the different stages of sleep differently. For example in one study, a low-carb meal improved NREM sleep (the first 4 stages of sleep) while a higher-carb control (70% carb) improved REM sleep (Source: NCBI).

The author concluded that the evidence is too limited to make concrete assumptions, but high-GI carbs consumed 4 hours before bed, may enhance sleep quality and latency. Again, it is almost impossible to say that the highGI carbs increased amino acid uptake increasing free tryptophan in the blood. It very well could have been that people were more tired after the insulin spike caused by high carb intakes, increased glucose uptake and dropped blood sugar.

Diet Quality

The above looked at manipulating acute meals to potentially enhance sleep. But what about longer term (chronic) approaches, can they provide more impactful results?

The author dives briefly into a couple of studies examining high-protein, high-carb and high-fat diets, and how they impacted several indices of sleep. In alignment with results from above, a lowcarbohydrate diet (50g/day) in post-menopausal women increased REM latency (time taken to reach REM sleep) (Source: NCBI). She also highlights another 4-day study in 44 adults, that showed improved sleep latency (shorter time to fall asleep) when following high-carb diets (56% carb). However, in this study, higher-protein diets decreased waking episodes (e.g. sleep-cycle disruptions).

Finally, the author mentions a cross-sectional study of over 400 postmenopausal women, where the only factor that was significantly linked with reduced overall sleep time, was higher fat intakes

Tryptophan Supplementation

“If we need more tryptophan to produce melatonin, can’t I just supplement it?” Good point! The author talks very briefly about this, but references a more comprehensive review of it, which I will dive into briefly now!

As expected, they looked at several studies examining tryptophan supplementation at night. This is absorbed and converted to serotonin, than to melatonin and may heighten one’s sleep pressure or feelings of sleepiness by the action of melatonin on the “internal milieu” (Source: NCBI).

In this study, researchers examined a range of studies examining the effects of varying doses of tryptophan supplementation on insomniacs as well as healthy volunteers. Remind me to address the importance of this in the takeaway section! Anyway, from this comprehensive study, it appears that in both sleep-suffering and healthy participants, tryptophan supplementation (1g - 10g) can improve latency, sleep quality, latency to REM sleep and subjective feelings toward sleep.

Melatonin Supplementation

Melatonin supplementation essentially cuts out the middle man of tryptophan. It provides a direct, exogenous supply of the hormone responsible for winding down the body and preparing it for slumber. The author highlights the well-known mixed findings with regards to melatonin supplementation. However, she does mention a meta-analysis that showed an overall improvement in sleep latency of 7.2 mins overall (Source: NCBI).

Interestingly, the authors spends the majority of time in this section talking about tart cherry juice, which has been known to increase melatonin levels. This has been shown to be efficacious in those with sleep disorders, when consumed over a 1-2 week period.

Valerian Root

Valerian has been known to have a relaxing or calming effect on subjective sleep quality, which is why it has been the subject of several investigations. On this note, any supplement that is used to improve relaxation may be effective in improving sleep quality, latency and subjective ratings.

An important note here, highlighted by the author, is that some may have allergic responses to these extracts, and so should be cautious of this. Also, she mentioned that because of the potentiating impact valerian can have on growth hormone, this can cause issues when being tested in elite sport.

Conclusion

All of the above supplements are focused on increasing melatonin levels in the body.

This however, is not the only way of improving your sleep. In fact your intake of tryptophan, and tryptophan:other amino acids, ratio may already be optimal for getting a great night’s sleep, but you are coming up short in the other major areas. These include practicing proper sleep hygiene and regularity of your sleep schedule.

Don’t look to these highly specific strategies while going to bed at 2:30 AM and falling asleep on the couch watching TV. They will have NO effect here.

Takeaways - Food for Thought

1. Don’t major in the minors. Manipulating specific aspects of the diet will provide little to no benefit if you are not practicing proper sleep hygiene and regularity

2. Tryptophan is the amino acid precursor to serotonin and melatonin may be beneficial

3. To promote tryptophan influx and availability, high-carb meals (especially high-GI) consumed 3-4 hours before bed

4. High-protein diets may help reduce wakeful episodes

5. Melatonin supplementation may help to improve sleep latency in those with sleep disorders, and help healthy individuals travelling across different time zones, but results are mixed

6. Tart cherry juice may increase melatonin levels and promote sleep quality, and reduce sleep latency

7. Tryptophan supplementation at night seems to be effective in both healthy individuals and those with sleep disorders for improving sleep parameters.

8. Valerian and other calming/relaxing remedies may help to promote sleep quality through down-regulating arousal and activation - moving the body closer to restfulness.