Rumor: A cup of warm milk at night can help you get to sleep easily.
Truth: It’s not so much that the tryptophan helps people get to sleep, but for some reasons it seems like the placebo effect produced from the belief that milk plays the role of hypnosis actually does the help. If you continue to firmly believe in this, then maybe milk can really heal your insomnia.
Milk does contain L-tryptophan, which is capable of producing serotonin and melatonin that are both helpful hormone for inducing sleep. This is also why the rumor is well known—there is kinds of scientific basis. However, in addition to milk, meat products also widely contain tryptophan and the total amount of tryptophan in a serving of food is not sufficient to fluctuate human’s hormone levels.
Moreover, there is a blood-brain barrier (BBB) which separates the blood and our vulnerable brain. The BBB protects the brain from the invasion of foreign matters, but it also impedes the entrance of some beneficial substances in the same time. Thus, any substance that helps sleep must penetrate this barrier before it can take effect. As you may know, milk is rich in all kinds of amino acids (of course including tryptophan), however the protein-rich food can lead to universal increase in different amino acids in our blood, and these amino acids compete with each other to penetrate the BBB—just imagine the entrance of a metro station during rush hours—the ability of tryptophan to penetrate the BBB actually decreases.
Rather than drinking a cup of warm milk to help you sleep, it would be a better choice to have some cookies. It is well known that people feel tired when they are full up, but why people have such feelings is still controversial. A hypothesis is that the carbohydrates stimulates pancreas islet to synthesize insulin, which allows amino acids rather than tryptophan to come through muscular tissues. Therefore, tryptophan becomes easier to enter human brain and then you feel sleepy. Another famous hypothesis is that massive food intake results in blood pushing to human gastrointestinal tract and decreased blood supply for human brain, which altogether lead to feeling of tiredness. However, the current research results tend to support that there is no obvious changes of blood through human brain before and after eating. Besides, even if such hypothesis stands, liquid foods will not have more significant effect than solid foods. That is to say, if you replace the warm milk with some other foods at night, you may be even easier to get asleep. And of course, you will also have better understanding of the saying:” a horse can’t get fat without an extra ration.”
By far, maybe some readers can speculate that by intake tryptophan during limosis may be helpful for sleeping and yep, this is the fact. There was US companies selling L- tryptophan tonic to heal insomnia and depression, but the products were recalled by FDA in the year of 1989, due to the possibility of causing a series of health issues. Yet, the correlation between the health issues and L- tryptophan is far from a final conclusion.
As a matter of fact, the thing that does the help is the warmness of the warm milk but not the warm milk itself. Study has revealed that people get easier to sleep when the skin temperature rises. But most often, a cup of warm milk is not enough to induce apparent temperature increasing on your skin. In contrast, a hot bath is much more effective.
Conclusion: A glass of warm milk can help sleep is mainly because of the placebo effect. If you keep on believing in this, then warm milk may be really helpful for your insomnia.
Remedial measure: In fact, it is the warmness of milk rather than the milk itself does the job of helping sleep. There is study concluded that people get to sleep quickly when skin temperature rises. But most often, a mug of warm milk is insufficient to rise the temperature of your skin. In a comparison, a hot bath contributes more.
- The New York Times. The Claim: A Glass of Warm Milk Will Help You Get to Sleep at Night
- Live Strong. Why Does Warm Milk Make You Sleep Better?
- Scienceline. Is it true that warm milk can make me sleepy?
- Go Ask Alice. Does warm milk really lull us to dreamland?