Don’t you hate feeling sleep deprived? I know I do! If I don’t get a good night's sleep, my day is ruined and my ability to function at an optimum level is severely compromised. Despite this knowledge, lack of sleep is an issue that I along with many others are confronted with!
There are many reasons why individuals fail to get enough sleep- stress, physiological issues, busy work schedules. Nutrition and exercise can also impact sleep. Specific foods or beverages as well as the timing of consumption may help to induce or interfere with sleep.
What is sleep and why is it important?
Sleep consists of two physiological states: Non-rapid eye movement sleep (NREM) and Rapid eye movement sleep (REM). NREM sleep is comprised of three stages that progress from lighter to deeper sleep. REM sleep tends to be characterized by rapid eye movement, intense dreaming and higher levels of brain activity.
The sleep-wake cycle is an essential circadian rhythm, which are 24-hour cycles that are part of the body’s ‘internal clock’ and enable us to perform processes essential to survival. The suprachiasmatic nucleus (SCN), located in the hypothalamus in the brain, is central to sleep and is often called “the master circadian clock," as it synchronizes cellular pathways that follow circadian rhythms, including digestion, absorption and metabolism. Circadian rhythms are influenced by zeitgebers, which are external cues that enable the body to maintain a synchronized clock and light is the strongest zeitgeber for the circadian system. Melatonin is a hormone that is essential to the sleep-wake cycle. The SCN has melatonin receptor cells and as darkness falls, melatonin is secreted by the pineal gland to induce sleep.
Sleep is important for many reasons, it allows the body to recharge and is vital to our function and survival. Sleep is also critical for the formation of memories and plays an integral role in learning and synaptic plasticity. Acute sleep deprivation and sleep disturbance may also impact adaptive immunity, which is associated with increased vulnerability to infectious disease. Sleep also plays an important role in metabolic functioning, including energy metabolism, glucose regulation and appetite. A systematic review by Khatib et al. in 2017 that investigated the effects of partial sleep deprivation on energy balance, found that energy intake significantly increased by 1611kj/day following partial sleep deprivation, compared to control subjects. These changes in energy intake were also found to be accompanied by a higher fat and lower protein intake.
As well as diet and exercise, adequate sleep is also essential to our health! Many individuals struggle to get enough sleep or even sleep too much. Nutrition interventions may help to combat these issues by interfering with the mechanisms of sleep, which are described above.
Foods that Impact Sleep
Caffeine:
Caffeine consumption impacts sleep, it is a stimulant that can interfere with both the duration and quality of sleep. Whilst caffeine may be beneficial for those struggling to remain awake, if you are looking to induce sleep, avoiding caffeine in the hours before bed may be of benefit. Caffeine promotes alertness by acting as an “adenosine receptor antagonist.” Adenosine is a molecule that promotes sleep onset and caffeine blocks the adenosine receptor which helps to prevent sleep. When Adenosine builds up in the bloodstream, it interacts with specific cell receptors to inhibit neural activity which causes drowsiness.
Coffee is not the only caffeine containing substance. Caffeine is also found in products such as energy drinks, certain supplements and chocolate. Certain teas also contain caffeine, so whilst you may drink herbal tea before bed, check that it does not contain caffeine!
Alcohol:
Alcohol is a central nervous system depressant, that causes brain activity to slow down. However, whilst alcohol has sedative effects studies have shown that alcohol consumption interferes with sleep quality and duration. Drinking alcohol can interfere with REM sleep. Since alcohol is a sedative, consumption may lead to a shorter sleep onset time and may cause individuals to fall into a deep sleep quickly. However, an imbalance may occur between slow-wave sleep and REM sleep, throughout the night. As a result alcohol consumption tends to interfere with both sleep quality and duration.
Insomnia is a common sleep disorder, it is defined as “a persistent difficulty with sleep initiation, duration, consolidation and quality.” Insomnia often leads to excessive daytime sleepiness and since alcohol consumption may reduce REM sleep and cause sleep disruption, drinking alcohol before bed may result in symptoms related to insomnia.
Kiwi:
Kiwi has a high serotonin content, which may contribute to improved sleep. Kiwi is also high in folate and a folate deficiency may be linked to insomnia and restless leg syndrome. Folate is often destroyed in the cooking process, however kiwis are typically consumed raw4.
Tryptophan: milk, turkey, chicken, fish, eggs, pumpkin, seeds, beans, peanuts, cheese, leafy greens
The conversion of tryptophan to serotonin, which is then converted to melatonin is dependent on sufficient precursor tryptophan availability in the brain. This is aided by the consumption of foods rich in tryptophan.
Melatonin: cow’s milk and tart cherries
Foods high in melatonin have been found to help with sleep onset. Cow’s milk is often said to have sleep promoting benefits. Melatonin occurs naturally in cow’s milk and the concentration of melatonin may increase if cows are milked in the darkness, this can help to induce sleep.
Tart cherries are also a source of melatonin. One study indicated that consumption of tart cherries increased sleep duration and quality. The study found that individuals who were given tart cherry juice supplementation had an increase in melatonin levels. These individuals were found to spend a longer time in bed (+24 minutes), to have an increase in total sleep duration (+ 34 minutes) and improved sleep efficiency, with a significant reduction in daytime napping (-22%) (p< 0.05). Another study found that tart cherry juice consumption resulted in a significantly reduced insomnia severity index score (13.2 ± 2.8 versus control 14.9 ± 3.6; p < 0.05) and wake after sleep onset time (62.1 ± 37.4 min versus control, 79.1 ± 38.6 mins; p < 0.01), in older females with insomnia
Magnesium: kale, spinach, quinoa
Magnesium enhances melatonin secretion. It is important for the production of the enzyme N-acetyltransferase which converts 5-HT into N-acetyl-5-hydroxytryptamine, which can then be converted to melatonin. The study, Magnesium Intake and Sleep disorder Symptoms: Jiangsu Nutrition Study of Chinese Adults at Five-year Follow-Up, in 2018 found that dietary magnesium consumption was inversely associated with falling asleep during the day in women. A magnesium deficiency may also result in muscle cramps, which can contribute to muscle cramps and contribute to poor sleep. Consuming magnesium may reduce nighttime wakefulness and maintain a ‘normal sleep structure.’
Chamomile:
Drinking chamomile tea can induce sedation. Chamomile contains apigenin, which is a chemical compound found in many plants. When apigenin binds to the GABA receptors in the brain it can induce a sedative effect. GABA is a neurotransmitter that functions to inhibit the central nervous system and activation of GABA (A) receptors can help to induce sleep onset.
Eating Patterns and Sleep Quality
The timing and quantity of meals may impact sleep. Large portions sizes and/or meals late in the evening impact sleep as the thermogenic effect of digestion can affect circadian rhythms. Nutritional intake has been recognized as a zeitgeber and, “eating out of sync with our master biological clock (eating at night when our master clock is signaling us to sleep) has been hypothesized to contribute to adverse cardio metabolic health”.
High glycemic carbohydrates and low protein intake may help to induce sleep. Tryptophan is a neurotransmitter involved in the sleep-wake cycle that is converted into serotonin, which is then converted to melatonin. Melatonin is released by the pineal gland to induce sleep. Tryptophan is transported across the blood brain barrier by a system that shares transporters with amino acids, LNAA.
Increasing the ratio of tryptophan to LNAA in the blood through a high carbohydrate and low protein intake may help to induce sleep, by enabling for an increase in melatonin production.
Insulin also influences the transport of tryptophan across the blood brain barrier after a rich carbohydrate meal and it facilitates the uptake of LNAA by the muscles. Consumption of high glycemic carbohydrates increases the levels of circulating ratio of tryptophan through insulin action.
Key Take Aways
Sleep is essential for optimum health and some of the foods we eat can impact our sleep without us even knowing! Gaining an awareness of the types of foods and practices that may interfere with sleep, as well as becoming educated on best nutritional practices is critical to our health, and can help to combat against the onset of chronic disease.
Sources:
https://www.bda.uk.com/resource/chrono-nutrition-a-new-dietary-dimension.html
https://link.springer.com/article/10.1007%2Fs00394-011-0263-7
https://pubmed.ncbi.nlm.nih.gov/11983310/
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