Global warming is a major threat affecting “increasing heat stroke” and “chronic inactivity related to summer heat (Natsubate (summer fatigue))”. Numerous review articles have described heat stroke in detail, however to our knowledge, there is no review article on the prevention of both heat stroke and Natsubate. In this paper, we speculated on the pathophysiology of Natsubate with reference to findings of heat stress, exercise, and water regulation. Subsequently, a balanced heat stroke and Natsubate prevention methods is discussed based on the pathophysiology of heat stroke and the inferred pathophysiology of Natsubate. Heat stress due to summer heat can lead to leaky gut and also dysautonomia via the brain-gut axis. On the other hand, intensified drinking behavior to reduce heat stress (overhydration, rapid rehydration, and extreme internal cooling) also leads to water intoxication and dysautonomia. Water intoxication and dysautonomia due to these factors are assumed to be the pathophysiology of Natsubate. If too much focus is placed on heat stroke prevention, healthy lifestyle and heat acclimatization may be impaired, and the body and mind may become more susceptible to heat stroke and Natsubate. In order to prevent both of heat stroke and Natsubate, it is thought that by daring to improve maximal oxygen intake and heat acclimatization even under summer heat, we can create a body and mind that prevents heat stroke and Natsubate. On the other hand, these efforts under summer heat may lead to heat stroke and Natsubate, making it difficult to strike a balance. The key to this balance is to refrain from raising the body core temperature too high and engaging in too strenuous activities, and to practice proper hydration.

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