Why Does Milk Make Me Sleepy?
Milk's association with sleepiness is a long-standing belief, but the science is nuanced. While milk does contain tryptophan, an amino acid that the brain uses to produce serotonin and melatonin (compounds promoting relaxation and sleep), the amount in a typical serving is insufficient to induce drowsiness. [1, 7] The perceived sleep-promoting effect might stem from other factors:
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Psychological Association: The comforting ritual of warm milk before bed, often associated with childhood, creates a psychological link between milk and sleep. [5] This learned association, rather than a physiological effect of the milk itself, can contribute to feelings of sleepiness.
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Lactose Content: Some individuals might experience tiredness due to lactose intolerance. Excess lactose in the body can lead to physiological fatigue. [9] However, this is a separate issue from milk's inherent sleep-inducing properties.
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Other Compounds: Besides tryptophan, milk contains other compounds, like melatonin, which might contribute to relaxation and sleepiness, although their effects are likely minor. [3, 4]
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Warm Temperature: The warmth of the milk itself may have a relaxing effect, contributing to feelings of sleepiness. [6] This is a placebo-like effect, as the warmth is a separate factor from the milk's constituents.
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Routine and Timing: Drinking milk as part of a regular bedtime routine can reinforce the association between milk consumption and sleep. The timing of consumption (close to bedtime) may also play a role, regardless of the milk's effect.
The Myth Debunked
The idea that milk directly makes you sleepy is largely a myth. While milk contains substances that could theoretically promote sleep, the amounts are too small to have a significant effect. [1, 7] The perceived sleepiness is more likely attributable to psychological factors, individual lactose tolerance, or the relaxing effect of a warm drink before bed. The effectiveness of warm milk for sleep is primarily a result of learned associations and comforting routine.
