Why is milk preferred at night? The scientific and historical reasons

November 30, 2025 •

4 min read

According to the Centers for Disease Control and Prevention, approximately one in three adults in the U.S. doesn't get enough sleep. For centuries, many have turned to a simple solution, which is why is milk preferred at night, as it offers a natural, comforting way to wind down and improve rest.

Quick Summary

Milk is often preferred at night due to its content of tryptophan and melatonin, which promote better sleep. It also contains protein like casein for muscle repair and provides a soothing psychological ritual that aids relaxation before bed. Certain nutrients also support overall health.

Key Points

Tryptophan and Melatonin: Milk contains tryptophan, which the body uses to produce serotonin and melatonin, hormones crucial for regulating the sleep-wake cycle.
Night Milk Advantage: Milk collected at night has higher levels of tryptophan and melatonin, enhancing its natural sedative effects.
Casein Protein for Recovery: The slow-digesting casein protein in milk provides a steady stream of amino acids overnight, supporting muscle repair and growth.
Psychological Comfort: The warm temperature and habitual consumption of milk can act as a psychological cue for relaxation, signaling to your body that it's time to rest.
Satiety and Hunger Control: Drinking milk can keep you feeling full, preventing late-night hunger that might otherwise interrupt your sleep.
Digestive Considerations: Individuals with lactose intolerance may experience digestive discomfort that disrupts sleep, making milk a poor choice for them.
Warmth vs. Nutrients: While the warmth is a comforting ritual, there is no strong evidence that warm milk is nutritionally superior to cold milk for sleep promotion.

A warm glass of milk before bed is a timeless tradition, passed down through generations. While its calming effect has often been attributed to folklore, modern science offers concrete explanations for why many people find this nightly ritual so effective. This comprehensive guide explores the nutritional science, physiological effects, and psychological comfort that make milk a preferred nighttime beverage.

The Scientific Connection: Tryptophan, Melatonin, and Serotonin

The primary scientific reason that drinking milk can promote sleep lies in its unique amino acid and hormone content. Milk is a natural source of tryptophan, an essential amino acid that plays a crucial role in the body’s production of key neurochemicals related to sleep.

The Tryptophan Pathway

Tryptophan is converted by the body into serotonin, a neurotransmitter that helps regulate mood, induce relaxation, and create a sense of well-being.
As evening progresses, serotonin is then converted into melatonin, the hormone that controls the sleep-wake cycle (circadian rhythm) and signals to your body that it's time to prepare for sleep.
Recent research even indicates that milk collected from cows milked at night contains significantly higher levels of tryptophan and melatonin compared to daytime milk, enhancing its sedative effects.

Muscle Repair and Satiety

Beyond its role in promoting sleep hormones, milk provides valuable nutrients that support your body throughout the night. It is an excellent source of protein, specifically casein and whey.

Slow-Digesting Casein: Casein makes up about 80% of the protein in milk. It forms a gel-like curd in the stomach, leading to a slower, more sustained release of amino acids into the bloodstream. This steady supply of protein throughout the night can aid in muscle repair and recovery, particularly beneficial for athletes or those who work out in the evening.
Long-Lasting Fullness: The high protein content and slow digestion of casein help keep you feeling full for longer. This can prevent late-night hunger pangs and cravings for unhealthy snacks that might otherwise disrupt your sleep.

The Soothing Psychological Ritual

While the nutritional components are significant, the psychological aspect of a glass of warm milk is also a powerful factor. Creating a consistent bedtime ritual can train your brain to recognize that it is time to wind down.

Comfort and Warmth: The act of holding and sipping a warm beverage is inherently soothing. It can help calm the nervous system and reduce stress and anxiety that often interfere with falling asleep.
Nostalgic Comfort: For many, warm milk is a comforting throwback to childhood, evoking feelings of safety and relaxation. This nostalgic association can create a positive psychological cue that makes it easier to fall asleep peacefully.

Potential Drawbacks and Considerations

Drinking milk at night is not for everyone. Some individuals should consider alternatives to avoid potential side effects that could disrupt sleep.

Lactose Intolerance: For those who are lactose intolerant or sensitive to dairy, consuming milk before bed can cause significant digestive issues such as bloating, gas, or diarrhea. These symptoms can easily interfere with a good night's rest.
Calorie Intake: For people watching their weight, the calories and fat in milk are a consideration. While a small amount is unlikely to be an issue, consuming milk in excess could add extra calories to your daily intake. Opting for low-fat or skim milk can mitigate this, while still providing many of the sleep-supporting nutrients.

Warm vs. Cold Milk Comparison

The choice between warm and cold milk is often debated. Here is a comparison of their respective benefits for nighttime consumption:


Feature	Warm Milk	Cold Milk
Psychological Effect	Generally considered more comforting and soothing, signaling relaxation to the body.	Less of a traditional calming ritual, although personal preference is a major factor.
Digestion	May be easier to digest for some individuals, reducing the risk of nighttime stomach discomfort.	Can be less soothing and potentially counterproductive for those prone to digestive issues like acid reflux.
Nutritional Content	The nutritional content is the same, but the warmth can enhance the psychological comfort factor.	Provides the same essential nutrients, including tryptophan, calcium, and protein.
Sleep-Inducing Compounds	No definitive evidence suggests warm milk delivers more sleep compounds than cold milk.	Contains the same sleep-promoting compounds, but lacks the comforting warmth.

The Role of Milk in a Broader Sleep Hygiene Strategy

Incorporating milk into your routine is most effective when combined with other good sleep practices. A holistic approach ensures you address all potential factors affecting your rest. For example, maintaining a consistent sleep schedule, creating a relaxing pre-sleep environment, and avoiding stimulants like caffeine before bed will complement the effects of drinking milk. Additionally, regular exercise during the day is known to improve sleep quality. The combination of these habits, with milk as a nutritional component, can significantly enhance your ability to fall and stay asleep.

Other Sleep-Promoting Foods

If milk is not an option, other tryptophan-rich foods include turkey, eggs, nuts, and seeds.
Herbal teas like chamomile also offer a warm, comforting ritual that can aid relaxation without the dairy content.
Reducing exposure to blue light from screens in the hours leading up to bed helps regulate your body's natural sleep-wake cycle.

Conclusion

Ultimately, the preference for milk at night is a blend of scientific and psychological factors. From the hormonal cascade initiated by tryptophan and melatonin to the comforting ritual of a warm beverage, milk offers multiple pathways to help the body and mind prepare for sleep. While it’s a beneficial habit for many, individuals should consider their own health needs, particularly regarding lactose tolerance. For those who can enjoy it, a glass of milk can be a simple, effective part of a healthy, restorative nighttime routine, contributing to better sleep quality and overall well-being. For more information on creating a positive sleep environment, consult resources on proper sleep hygiene like those from the Sleep Foundation.

Frequently Asked Questions

While both warm and cold milk offer the same sleep-promoting nutrients, the warm temperature provides a psychological and physiological calming effect for many people, which can aid relaxation before bed. Ultimately, the best choice depends on personal preference.

Yes. Milk is rich in casein protein, which digests slowly. This slow digestion provides a sustained release of amino acids overnight, supporting muscle repair and recovery while you sleep.

Yes, for lactose-intolerant individuals, drinking milk at night can cause bloating, gas, and stomach cramps, which could significantly disrupt your sleep. Lactose-free alternatives or fermented dairy like yogurt might be better options.

A single, moderate glass of milk at night is unlikely to cause weight gain unless it contributes to a significant daily calorie surplus. In some cases, the satiety from milk may even prevent late-night overeating.

While the comforting ritual of drinking milk contributes a psychological element, milk also contains actual sleep-promoting compounds like tryptophan and melatonin, so it's not purely a placebo effect.

'Night milk' is milk collected from cows during night hours. It is reported to have naturally higher concentrations of melatonin and tryptophan, potentially making it more effective as a sleep aid than milk collected during the day.

This is a common belief, but scientific evidence is limited and inconclusive. Studies suggest that drinking milk does not actually increase mucus production in most people.