Does sleep-inducing milk help sleep? New findings reveal truth

Author: Liu Yuxin, Attending Physician in the Department of Otolaryngology at Xiyuan Hospital, China Academy of Chinese Medical Sciences, and Council Member of the Sleep Medicine Professional Committee of the World Federation of Chinese Medicine Societies. Review: Sun Shuchen, Chief Physician of the Department of Otolaryngology at Guang'anmen Hospital, China Academy of Chinese Medical Sciences, and President of the Sleep Medicine Professional Committee of the World Federation of Chinese Medicine Societies. Produced by: Science Popularization China. The cover image of this article is sourced from a licensed image library. Reposting may lead to copyright disputes.

Milk is not a direct sleep aid; however, it contains nutrients that may promote sleep support. You may have heard statements such as, 'Drinking a glass of milk or yogurt before bed can help with sleep,' or 'My child is stressed from studying; giving him milk before bed can help him sleep and provide calcium.' A professional will clarify: What exactly does drinking milk before bed provide?

Milk has beneficial nutrients like casein, lactoferrin, calcium, various vitamins, saturated fatty acids, and lactose. Once consumed, the stomach secretes gastric acid and digestive enzymes while the small intestine releases proteases, and the pancreas produces trypsin, which breaks down large molecules into smaller amino acids for absorption. This entire process takes between 2 to 6 hours. A 200ml glass of milk before bed contains about 84mg of tryptophan, but only 1% to 2% of that can enter the serotonin synthesis pathway. Moreover, the production of melatonin requires several hours to days, meaning that it cannot provide an immediate sleep aid effect.

Additionally, the proteins and fats in milk can trigger insulin secretion. A report published in Cell in 2019 noted that nighttime snacks can influence sleep quality; in experiments with mice, insulin impacted the accumulation of the PER2 protein, thereby affecting the body's sleep-wake cycle. Studies have indicated a negative correlation between the ratio of saturated fatty acids in dinner and the amount of deep sleep. Another study found that eating during sleep hours caused significant weight gain in mice. Thus, consuming milk before bed might actually disrupt sleep patterns and lead to fat accumulation.

Furthermore, the proteins found in milk can stimulate gastric mucosal cells to secrete gastrin, which enhances gastric acid secretion. Calcium ions can also encourage gastrin production to exceed normal fasting levels at night. Consequently, there is an increased potential for gastric acid reflux, which can cause pharyngitis. Of course, opting for a midnight snack raises the likelihood of developing reflux pharyngitis.

In conclusion, the sleep-inducing effects of milk at bedtime are limited, and it may also contribute to dental caries, fat accumulation, and pharyngitis.