No, the sun itself doesn't directly cause sleepiness. Instead, several factors associated with sun exposure can lead to fatigue.
Factors Contributing to Sun-Induced Tiredness
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Dehydration: Excessive sweating in the sun depletes your body's water supply, leading to dehydration and fatigue. As noted by Cleveland Clinic, "Heat, humidity, excessive sweating and poor hydration can wipe you out and make you feel sleepy." (https://health.clevelandclinic.org/why-does-the-sun-make-you-tired)
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Vasodilation: Your blood vessels widen (vasodilation) in response to heat, diverting blood flow away from your muscles and brain, potentially causing fatigue. Dr. Ashwin Rao, as cited by the University of Washington Medicine, explains that "A lot of tiredness stems from dehydration and vasodilation." (https://rightasrain.uwmedicine.org/body/rest/sun-tired-tips)
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Increased Metabolism: The sun's heat increases your metabolic rate, meaning your body uses energy faster, potentially contributing to tiredness. This is highlighted by A. Vogel: "This increases metabolism (the rate at which you use energy) and can, in turn, contribute to tiredness." (https://www.avogel.co.uk/boost-your-energy/why-you-feel-so-tired-after-being-in-the-sun/)
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Circadian Rhythm Disruption: While sunlight usually regulates your circadian rhythm (sleep-wake cycle), excessive or unusual sun exposure can disrupt it, affecting sleep quality and causing daytime fatigue. Reduced sun exposure in winter can also cause disruption, as noted by Henry Ford Health: "Unfortunately, reduced sun exposure can dramatically affect your circadian rhythm, causing your body to produce more melatonin (a.k.a., the sleep hormone)." (https://www.henryford.com/blog/2021/01/more-tired-in-winter)
Importance of Hydration and Heat Safety
Feeling tired after sun exposure is common, but it's crucial to be aware of the signs of dehydration and heat illness. If you experience these, seek shade, rest, and rehydrate.
