Is "Tsuyu-bate" Sleep Discomfort Actually Related to "Gut Environment"? Self-Care for the Rainy Season from the Gut Revealed

June marks the start of the rainy season in many regions. During this period, many people suffer from vague discomforts such as "feeling generally unwell," "being tired but unable to sleep," or "having a heavy head" – commonly referred to as "Tsuyu-bate" (rainy season fatigue).

In fact, over 70% of people experience lethargy and sleepiness during the rainy season, with 30% attributing this to a decline in sleep quality (Note 1). However, not many are aware that disruptions in their gut environment are related to these issues.

According to a survey by the Ministry of Health, Labour and Welfare, approximately 1 in 5 adults in Japan (20%) do not get enough rest from sleep (Note 2), highlighting that poor sleep quality is a societal issue extending beyond the rainy season.

Interestingly, the gut environment has recently gained attention as one of the factors influencing sleep quality.

During this period of drastic changes in atmospheric pressure, temperature, and humidity, a phenomenon occurs where the "gut" and "sleep" become interconnected and disrupted. Recent research on gut bacteria has focused on the link between the gut environment and sleep quality. The rainy season is a time when the combination of changes in pressure, temperature, and humidity, difficulty sleeping, and irregular eating habits can easily lead to discomfort from both sleep and gut-related issues.

KEAN Health Inc. (Headquarters: Minato-ku, Tokyo; Representative Director: Kota Yamaji) explains countermeasures for "Tsuyu-bate" stemming from sleep problems, from the perspective of the gut environment.

Note 1: Asset Brain Consulting L.L.C-FZ "Survey on Lethargy and Sleep Conditions Before the Rainy Season" (2026)

Note 2: Ministry of Health, Labour and Welfare "Summary of the National Health and Nutrition Survey 2024"

Why Does Sleep Quality Decline During the Rainy Season?

The increase in sleepiness and lethargy during the rainy season is due to multiple factors, such as changes in atmospheric pressure and mugginess, simultaneously affecting the relationship between the gut and sleep.

When atmospheric pressure drops, the autonomic nervous system becomes imbalanced, leading to the sympathetic nervous system becoming dominant. Consequently, intestinal peristalsis decreases, disrupting the gut environment, while the body's core temperature becomes less likely to drop, hindering sleep onset. Furthermore, high humidity environments increase the temperature and humidity within bedding, leading to more frequent awakenings during the night. If this is coupled with loss of appetite or picky eating, it results in a shortage of dietary fiber and fermented foods, which are essential nutrients for beneficial gut bacteria. This can reduce the activity of useful bacteria that promote sleep quality.

When you can't sleep, your gut condition worsens, and when your gut condition is poor, you sleep even less. The true nature of "Tsuyu-bate" discomfort may be the accumulation of such vicious cycles.

Two Types of Gut Bacteria Related to Sleep Quality

Recent research is gradually clarifying the relationship between sleep and the gut environment. Among these, bacteria that have garnered attention for their reported association with sleep quality and nighttime awakenings are Faecalibacterium and Prevotella.

■ Faecalibacterium: Bacteria reported to be associated with nighttime awakenings

Faecalibacterium is known as a representative bacterium that produces butyrate, a type of short-chain fatty acid, in the gut.

A study involving Japanese individuals showed a tendency for fewer awakenings during sleep with higher amounts of Faecalibacterium. This suggests its potential role in maintaining uninterrupted sleep.

*Kitami et al., 2020

■ Prevotella: Bacteria reported to be associated with poor sleep quality groups

Prevotella is one of the bacteria that normally reside in the gut, and its abundance and function are known to change depending on diet and gut environment.

Sleep-related research has reported that certain types of Prevotella were characteristically found in groups with poor sleep quality. Another study also indicated that certain types of Prevotella may be associated with the PSQI score, an indicator of poor sleep quality.

*Seong et al., 2024 / Grosicki et al., 2020

Starting Today: "Gut-Centric" Rainy Season Fatigue Countermeasures

During the rainy season, the autonomic nervous system is prone to imbalance due to high humidity and changes in atmospheric pressure. Increased difficulty sleeping and mid-night awakenings can lead to next-day lethargy and decreased concentration.

First and foremost, it is crucial to create a comfortable sleep environment by eliminating mugginess in the bedroom. Utilizing air conditioners and dehumidifiers to maintain a comfortable room temperature and humidity is the first step in sleep management during the rainy season.

In addition to this, supporting the body from the inside by focusing on the gut environment is important.

In terms of diet, it is essential to consume a balanced intake of dietary fiber from sources such as vegetables, seaweed, mushrooms, beans, and whole grains. Dietary fiber serves as a nutrient source for butyrate-producing bacteria like Faecalibacterium.

Furthermore, foods containing tryptophan, such as soy products, dairy products, eggs, and bananas, should be incorporated as they are precursors for serotonin and melatonin.

When making dietary improvements, it is also beneficial to understand your current gut environment. Since gut flora varies among individuals, understanding your own gut condition before deciding on a care strategy will lead to more effective improvements.

Overview of Gut Flora Test "chatFLORA G"

Utilizing third-generation analysis technology, this test can analyze even rare bacterial species that were difficult to detect with conventional methods (Note). Based on your current diet and test results, it proposes personalized gut health strategies tailored to your individual gut environment.

*Conventional: Analysis methods targeting only a portion of the 16S rRNA gene using second-generation sequencers.

Product Details: https://keanhealth.jp/lp?u=chatflora-g-pr

About KEAN Health Inc.

Over 20 years have passed since the completion of the Human Genome Project, and biotechnology has evolved into an era of "Bio-Transformation," contributing to the resolution of societal issues and economic growth. KEAN Health Inc. operates with the vision of making genome and gene analysis, previously utilized mainly by researchers and specialists, more accessible to the general public.

Company Overview:

Company Name: KEAN Health Inc.

Headquarters: Canal Square Shibaura 4F, 3-14-18 Shibaura, Minato-ku, Tokyo

Representative Director: Kota Yamaji

Website: https://keanhealth.co.jp/

Contact for Inquiries:

Department: Public Relations

Email: press@keanhealth.co.jp