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Up to article 5, we introduced daytime activities to improve your level of alertness, but from here, we would like to introduce methods for a good night's sleep.
When preparing for sleep mode, dinner is an important factor. Let's take a closer look at its content.
Foods to eat for dinner
To sleep soundly at night, it is recommended to eat foods that cool the body. For example, chilled tomatoes. Eating chilled foods that have a cooling property makes it easier to lower your body temperature, which is effective. For other vegetables and fruits, generally, those in season in summer, leafy vegetables, those with high water content, and those suitable for cultivation in tropical countries tend to apply. Other examples include white sugar, soba, konjac, milk, and green tea (※1).
Also, physically, well-chilled soft drinks, ice, and ice cream also fall under things that cool the body.
There are many recipes using these ingredients available online and in cookbooks, so try to incorporate them into your dinner continuously with some creativity. Please note that chilled tomatoes merely prepare you for sleep, they do not induce sleep. Also, eating too much can upset your stomach.
Things effective for deep sleep besides cooling the body
Besides things that cool the body, things known to be good for sleep include Eastern herbal medicines and Western herbs such as valerian and chamomile. While the detailed verification of their effects may not have been conducted, the fact that they have been used for hundreds of years and are now recognized worldwide can be considered evidence that they have some degree of effect.
In addition, there are sleeping pills and supplements, but some of them include products with strong side effects or lacking scientific evidence, and even if you take specific ingredients with proven scientific evidence, they may not work as intended in your body (the original effect may not be exerted).
Furthermore, sleep often improves simply by maintaining a balanced diet, a regular lifestyle, and lifestyle improvements such as weight loss. Therefore, instead of easily jumping to medications or supplements, it is advisable to make an effort to obtain accurate information by researching or consulting a specialist when using them.
Reasons to eat foods that cool the body
Humans are homeothermic animals, and body temperature is adjusted to be almost constant by homeostasis. However, body temperature is influenced by the naturally occurring approximately 24-hour internal clock (circadian rhythm), and undergoes a slight diurnal variation of approximately 0.7 degrees per day.
Strictly speaking, there are two types of body temperature: temperature of the hands and feet (skin temperature) and temperature inside the body (core body temperature). During daytime wakefulness, skin temperature is low and core body temperature is high, with a maximum temperature difference of approximately 2 degrees. Conversely, during sleep, skin temperature is high and core body temperature is low, and the temperature difference is within 2 degrees. This is because core body temperature is lowered by heat dissipation from the hands and feet (extremities), which have a large surface area, and by lowering core body temperature, organs, muscles, and the brain are allowed to rest.
What is important here is that reducing the difference between core body temperature and skin temperature is necessary for smooth sleep onset. The smaller the temperature difference, the stronger the sleepiness becomes, so consciously consuming foods and drinks that have the property of lowering core body temperature at dinner is effective.
The necessity of dinner
Some people skip dinner for dieting, but they might get hungry in the middle of the night and eat a late-night snack, or not be able to sleep due to hunger.
In fact, skipping dinner is said to increase appetite and heighten the likelihood of becoming more awake and unable to sleep.
This phenomenon involves a hormone called orexin. If you don't eat dinner, orexin neurons (neurons that release orexin) in the hypothalamus of the brain release orexin, and orexin's action is enhanced at its own orexin receptors, maintaining a high state of orexin neuronal activity (※2).
When orexin, which has the effect of promoting appetite and arousal, is activated, wakefulness is maintained, making it difficult to sleep. In addition, orexin also causes activation of the sympathetic nervous system and an increase in body temperature, which can lead to autonomic nervous system imbalance and various physical ailments.
You should eat dinner, but eating too much takes longer to digest and can easily cause stomach upset, so we recommend eating until you are about 80% full, with the goal of finishing two hours before bedtime. Also, be careful not to consume too much water, as it can increase urination and make you more likely to wake up in the middle of the night to use the restroom.
【References】
※1: Terumo Body Temperature Research Institute, Cold Sensitivity Countermeasures "Food" Edition
※2: Elucidation of the neural mechanism that raises the brain's "wakefulness" level, Japan Science and Technology Agency, Press Release H22/9/22
