Earlier experiments had demonstrated this effect, but it was unclear whether the gas was doing this itself or was acting indirectly by lowering body temperature, which also reduces metabolism.

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If you're planning on taking a polar bear plunge, Tipton says you can prime your body for the event several days before by gradually lowering the temperature of your shower.

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One is exhaust gas recirculation, which pumps cooled exhaust back into the engine air intake, lowering the combustion temperature and reducing NOx formation.

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"We aren't sure why activity primes your body for sleep so well, but it's likely a combination of factors, including lowering your core body temperature, increasing the sleep-promoting hormone melatonin and supporting a biological need to restore energy levels and repair cells and tissues when you sleep, " Cardinal says.

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Actually, alcohol in excess, can lead to a lowering of your core body temperature and place you at risk for hypothermia.

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