FULL CLAIM: “Onions can help you sleep through the night”; “Onions know when you’re stressed, and they release a chemical called tryptophan which is an amino acid that acts as a sedative”; "the RSV cure with the onions is just the tip of the iceberg"
REVIEW
Folk remedies often suggest that onions can help alleviate symptoms of respiratory illnesses. These alleged healing properties of onions surface frequently in social media posts, with users recommending various methods for using onions to boost immunity and combat illness (examples here, here, and here). Science Feedback previously found a lack of scientific evidence for an example of one such claim—that placing raw onions on the feet can cure illness.
In October 2024, another post of this ilk circulated on Facebook, claiming that onions are a natural sedative that can “help you sleep through the night” because they contain the amino acid tryptophan. It also claimed that onions can cure respiratory syncytial virus (RSV). At the time of writing, the reel had received more than one million views.
The primary speaker in the video, Esther Candace Brubaker, goes by the handles earthenchild on TikTok and poshmomma_ on Instagram; in total, these two accounts have more than one million followers. Brubaker was charged with homicide in 2013 after running over her boyfriend with her car in Cumberland County, Pennsylvania, according to reports from USA Today and various local publications.
Is tryptophan a natural sedative?
Tryptophan is one of nine essential amino acids that the body needs but can’t make on its own, necessitating its consumption by way of tryptophan-rich foods through a person’s diet. It’s primarily found in protein-rich foods such as meat, seafood, and dairy[1].
The U.S. Department of Agriculture estimates that a 100 gram (g) serving of raw onion contains approximately 14 milligrams (mg) of tryptophan. In comparison, 100g servings of other foods such as chicken breast, lamb, and cheddar cheese each individually contain more than 400 mg of tryptophan[1]. Thus, the claim that onions are “rich in L-tryptophan” is conjectural; in reality, other foods are comparatively richer in tryptophan.
The notion that tryptophan acts as a natural sedative may come from the fact that tryptophan is used to produce serotonin, a neurotransmitter that helps to regulate sleep. This is likely the basis for the claim that onions are a “natural sedative”. For context, this is also the root of the common myth that consuming turkey at North American Thanksgiving dinners causes drowsiness. However, according to the American Chemical Society, “turkey contains no more tryptophan than other types of meat. It’s more likely that the consumption of copious quantities of all kinds of food prompts our post-turkey feast naps.”
Evidence for tryptophan as a natural sedative when consumed through one’s diet is currently limited. One systematic review did find that tryptophan supplements administered at doses above one gram resulted in fewer sleep disruptions compared to individuals given less than one gram[2]. For context, the suggested amount of daily dietary tryptophan for adults is 3.5mg/kilogram (kg) of body weight, which amounts to roughly 250mg for a person weighing 70kg.
However, the authors of this review cautioned that the “exact mechanism of the sedating effect of [tryptophan] has not been fully elucidated”, and that more studies are needed to determine with greater certainty whether tryptophan supplements improve sleep quality.
Claim that onions are a natural sedative doesn’t stem from scientific evidence
In the reel, Brubaker claimed that onions “release” tryptophan, which can help you fall asleep and stay asleep throughout the night.
However, the content she cited to support her claim doesn’t come from scientific research. Rather, it’s the first Google search hit for the phrase “onions help you sleep”, linking to a marketing blog post from M&P Engineering, a UK-based food processing equipment manufacturer. The blog post, titled “How onions can improve sleep and relieve stress”, doesn’t provide any references for the claims it makes regarding L-tryptophan in onions acting as a natural sedative.
Further, Brubaker shared no evidence to support the claim that onions “release” tryptophan into the air.
Onions do release a chemical compound called sulfenic acid when they’re cut or crushed. This compound converts into molecules that irritate the lacrimal glands, which is why cutting onions often makes people cry[3].
However, the biological process by which tryptophan converts into serotonin occurs within the body[4]. It’s not as a result of breathing in tryptophan through the air. And as previously explained, it’s serotonin that plays a role in sleep quality, not tryptophan.
No evidence supporting onions as a “cure” for RSV or any other viral illnesses
In the October 2024 reel, Brubaker referenced a 2022 TikTok video where she promoted onion water as a cure for RSV and other respiratory illnesses (“we started with cutting [onions] up, putting them in water, getting rid of RSV”). This claim is unsubstantiated.
Jason Nagata, an assistant professor of pediatrics at the University of California, San Francisco, shared with the TODAY show online in 2022 that he wasn’t “aware of any scientifically proven studies that show any kind of benefit for colds or respiratory symptoms.” He added: “I just don’t think that people should expect that they’ll be able to really improve colds or flus with just onions.”
In an interview with AFP in 2022, epidemiologist Katrine Wallace expressed concern over claims of miracle onion cures, stating that “[o]nions aren’t going to hurt anybody, but if somebody is sick, they should seek actual medical attention. I am afraid that people will just drink onions and not seek medical care (and) they could spread Covid or the flu in the community.”
Science Feedback likewise searched PubMed, a repository of published scientific studies hosted by the U.S. National Institutes of Health, and found no evidence to support the claim that onion water cures RSV#.
Conclusion
While folk remedies like the use of onions for various health benefits have gained popularity on social media, there is little scientific evidence to support these claims. The assertions that onions can act as a natural sedative or cure for respiratory illnesses, including RSV, are unfounded.
# Pubmed search query: (allium cepa[Title/Abstract]) AND (Respiratory Syncytial Virus[Title/Abstract])
REFERENCES
- 1 – Zuraikat et al. (2021) Sleep and Diet: Mounting Evidence of a Cyclical Relationship. Annual Review of Nutrition.
- 2 – Sutanto et al. (2022) The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression. Nutrition Reviews.
- 3 – Silvaroli et al. (2017) Enzyme That Makes You Cry–Crystal Structure of Lachrymatory Factor Synthase from Allium cepa. ACS Chemical Biology.
- 4 – Höglund et al. (2019) Tryptophan Metabolic Pathways and Brain Serotonergic Activity: A Comparative Review. Frontiers in Endocrinology.
