Vitamin U is not actually a vitamin. It is the informal name for S-methylmethionine, a sulfur-containing compound found naturally in cabbage, spinach, and other vegetables, first identified in the 1940s when a researcher noticed that raw cabbage juice seemed to heal stomach ulcers in guinea pigs.1PubMed Central. S-Methylmethionine (Vitamin U): A Critical Narrative Review of Pharmacological Mechanisms, Evidence Levels, and Translational Barriers The “U” stands for “ulcus,” the Latin word for ulcer, and that origin story tells you most of what you need to know about how this compound earned its misleading name. The science around it is a mix of genuinely interesting biology and decades of hype that has outpaced the clinical evidence.
The Cabbage Juice Experiments That Started It All
In the late 1940s and early 1950s, physician Garnett Cheney at Stanford University ran a series of small trials testing raw cabbage juice on patients with peptic ulcers. In one of the more notable studies, thirteen patients with confirmed ulcers drank fresh cabbage juice daily. Cheney reported that the juice contained what he called an “antipeptic ulcer factor,” which he named vitamin U after demonstrating that it could prevent ulcers induced by histamine in guinea pigs.2PubMed Central. Rapid healing of peptic ulcers in patients receiving fresh cabbage juice A follow-up study at San Quentin Prison used a double-blind design: inmates with confirmed ulcer craters received either concentrated cabbage juice or a placebo, and after 22 days the cabbage juice group showed meaningful healing on X-ray.3PubMed Central. Vitamin U therapy of peptic ulcer; experience at San Quentin Prison
These studies were small and happened long before modern clinical trial standards, but they were enough to launch the idea that cabbage contained something special for the stomach. In some countries, particularly Japan, South Korea, and parts of Eastern Europe, vitamin U became a recognized pharmaceutical ingredient and is still sold as an over-the-counter supplement or added to gastric medications. In the United States and most of Western Europe, it never gained that same regulatory foothold and remains largely a curiosity of mid-century nutritional science.
What the Compound Actually Is
S-methylmethionine is a derivative of the amino acid methionine, with an extra methyl group tacked on. It is naturally produced by plants as part of their sulfur metabolism. When you hear it called “vitamin U,” that is a legacy label from Cheney’s era, not a designation endorsed by modern nutrition science. A true vitamin, by definition, is something your body needs and cannot make enough of on its own, leading to a deficiency disease when it’s missing. No deficiency disease has ever been linked to a lack of S-methylmethionine, and your body does not require it the way it requires, say, vitamin C or B12. The compound is better described as a vitamin-like or conditionally bioactive substance.4PubMed Central. S-Methylmethionine (Vitamin U): A Critical Narrative Review of Pharmacological Mechanisms, Evidence Levels, and Translational Barriers
In supplement form, it typically appears as S-methylmethionine sulfonium chloride, a stable salt. This is the form used in most research and in commercial gastric products sold in Asia and Eastern Europe.
Which Foods Contain It
Despite its association with cabbage, S-methylmethionine is found across a wide range of vegetables and some other plants. A study that measured vitamin U levels in 26 different food plants found that spinach had the highest concentration, at about 45 mg per 100 grams of dry weight, followed by pak-choi at about 34 mg, kale at roughly 23 mg, and then a cluster of greens including leaf mustard, broccoli, and asparagus all in the 18-20 mg range.5Food Science and Technology Research. Determination of Vitamin U in Food Plants Cabbage, the vegetable Cheney made famous, actually ranked lower than several of these greens.
Interestingly, the distribution within a single plant is uneven. In both Chinese and Western cabbage varieties, the middle portions of the leaves, including the midribs, contain the highest concentrations of the compound. The outermost leaves and the inner core have less.6Food Science and Technology Research. Determination of Vitamin U in Food Plants This means the part of the cabbage you eat matters. It also helps explain why Cheney’s raw cabbage juice, which included the whole leaf pulped and pressed, may have been more potent than eating a few pieces of cooked cabbage at dinner.
S-methylmethionine is also found in tea leaves. During the manufacturing of both green and black tea, heat exposure breaks down a portion of the compound into dimethyl sulfide, a volatile molecule that contributes to the aroma of brewed tea. Roughly 9-12% of the S-methylmethionine in tea leaves decomposes during the drying step alone, and steeping the tea in hot water degrades even more, with somewhere between 44% and 80% converting to dimethyl sulfide in the infusion.7PubMed. Formation of dimethyl sulfide from the decomposition of S-methylmethionine in tea (Camellia sinensis) during manufacturing process and infusion brewing So if you are hoping to get vitamin U from tea, you are mostly getting its breakdown product instead.
How It Protects the Stomach Lining
The mechanism behind S-methylmethionine’s gastroprotective effects has been studied most closely in animal models. When rats were given the compound before exposure to concentrated ethanol, a standard method for inducing stomach damage in the lab, it significantly reduced mucosal injury. The protective effect appears to work through sulfhydryl compounds, a class of molecules containing sulfur-hydrogen bonds that are important for maintaining the stomach’s protective mucus barrier. S-methylmethionine boosted the amount of surface mucin, the gel-like substance that shields the stomach wall from acid, by accelerating the secretion of deeper mucin stores toward the surface.8PubMed. Mechanisms for cytoprotection by vitamin U from ethanol-induced gastric mucosal damage in rats
This is a plausible and well-supported mechanism as far as animal evidence goes. More recent research has explored combining vitamin U with vitamin B5 (pantothenic acid) for treating erosive gastrointestinal conditions, with the rationale that B5 supports mucosal regeneration through a complementary pathway.9PubMed Central. Vitamin B5 and vitamin U review: justification of combined use for the treatment of mucosa-associated gastrointestinal pathologies The combination is used in some over-the-counter gastrointestinal products in Russia and parts of Asia.
The honest caveat here is that the clinical evidence in humans remains limited. Most of the peer-reviewed literature consists of preclinical work in cell cultures and rodents, with Cheney’s decades-old small trials being the primary human data. A 2025 narrative review put this bluntly: the most consistently reported effects are gastroprotective and antiulcer, but they have been observed predominantly in preclinical studies, and translational barriers remain significant.10PubMed Central. S-Methylmethionine (Vitamin U): A Critical Narrative Review of Pharmacological Mechanisms, Evidence Levels, and Translational Barriers This means the compound is promising, but it is nowhere near the level of evidence required for mainstream medical use in Western countries.
Skin and Wound Healing
Outside the gut, one of the more interesting lines of research involves the skin. S-methylmethionine sulfonium chloride, the salt form of the compound, has been shown to speed up wound closure in animal models when applied topically. In experiments with both physical cuts and chemical burns, treated wounds healed faster and showed better re-epithelialization, meaning the outer layer of skin regrew more completely compared to untreated controls.11PubMed. Accelerated wound healing by S-methylmethionine sulfonium: evidence of dermal fibroblast activation via the ERK1/2 pathway
The mechanism appears to involve activation of dermal fibroblasts, the cells responsible for producing collagen and rebuilding damaged skin tissue. A single treatment with the compound was enough to stimulate both the growth and the migration of human dermal fibroblasts in cell culture, and this effect was traced to activation of a specific signaling pathway called ERK1/2. When researchers blocked that pathway with a chemical inhibitor, the wound-healing boost disappeared.12PubMed. Accelerated wound healing by S-methylmethionine sulfonium: evidence of dermal fibroblast activation via the ERK1/2 pathway This gives the finding more mechanistic credibility than a simple observation that wounds healed faster.
Based on this and related research, S-methylmethionine is already commercially available in some skincare products marketed for wound healing and protection from ultraviolet damage.13PubMed Central. Effect of Enhancers on in vitro and in vivo Skin Permeation and Deposition of S-Methyl-L-Methionine Whether these products deliver clinically meaningful results on human skin in the real world is a separate question. The research establishing skin permeation of the compound focused on how enhancers could improve its absorption through the skin barrier, suggesting that getting enough of it to the right layer of skin is not trivial. Like the gastric evidence, the skin research is promising at the preclinical stage but far from conclusive for everyday use.
Organ Protection in Animal Studies
Researchers have also tested vitamin U’s protective effects on organs beyond the stomach and skin, although this work is entirely in animals so far. One notable study examined whether vitamin U could protect kidneys from damage caused by valproic acid, an anticonvulsant drug known to cause oxidative stress and inflammation in renal tissue. Rats treated with both valproic acid and vitamin U showed significantly less kidney damage than those given the drug alone. The protective effect worked across multiple pathways at once: oxidative stress markers went down, inflammatory signaling molecules dropped, and fibrosis indicators, the markers of scarring and tissue stiffening, decreased as well.14PubMed. Vitamin U has a protective effect on valproic acid-induced renal damage due to its anti-oxidant, anti-inflammatory, and anti-fibrotic properties
This kind of broad-spectrum protective activity is what makes vitamin U interesting to pharmacologists. Rather than acting on a single target, it appears to influence multiple processes simultaneously: dampening inflammation, neutralizing free radicals, and reducing tissue scarring. That sounds like a wonder drug on paper, but it is worth noting that many compounds look this good in rat models and fail to deliver the same results in humans. The jump from animal studies to human therapeutics is where most drug candidates stumble, and vitamin U has not yet made that jump in any rigorous, large-scale way.
A Role in Homocysteine Metabolism
One area where vitamin U’s biology is well understood at the molecular level is its role in sulfur amino acid metabolism. Your body has an enzyme called BHMT-2, which uses S-methylmethionine as a methyl donor to convert homocysteine into methionine. Homocysteine is an amino acid that, when it builds up in the blood, is associated with increased cardiovascular risk. The enzyme essentially takes the extra methyl group from S-methylmethionine and transfers it to homocysteine, recycling it into a useful amino acid.15PubMed Central. Betaine-homocysteine S-methyltransferase-2 is an S-methylmethionine-homocysteine methyltransferase
This is a real biochemical pathway and it is one reason some researchers speculate that diets rich in leafy greens could support healthy homocysteine levels through more routes than just folate and B12. However, it is unclear how much dietary S-methylmethionine actually reaches the liver in sufficient concentrations to make a meaningful dent in homocysteine levels. The enzymatic pathway exists, but the quantitative importance of this route relative to the better-known folate and betaine pathways has not been established in humans.
Why It Never Became a “Real” Vitamin
The label “vitamin U” has stuck around for over 70 years despite the scientific community never formally recognizing the compound as a vitamin. The reasons are straightforward. To qualify as a vitamin, a substance has to meet a few criteria: it must be essential for normal body function, must be needed in small amounts from the diet, and its absence must cause a specific deficiency disease. Think scurvy for vitamin C, beriberi for B1, rickets for vitamin D. No one has ever documented a disease caused by not consuming enough S-methylmethionine. Your body can synthesize methionine through other pathways, and S-methylmethionine’s methyl-donor role overlaps with compounds like betaine and folate that are already present in most diets.
In practice, the “vitamin” label persists mainly in countries where S-methylmethionine was approved decades ago as a pharmaceutical ingredient and grandfathered into the regulatory system. Japanese and Korean pharmaceutical companies, for instance, have marketed vitamin U-containing products for gastric complaints since the mid-20th century. In these markets, the name carries brand recognition and consumer trust that would be expensive to rebrand. In the Western supplement market, you can find vitamin U capsules and powders online, but they occupy a niche space without strong regulatory endorsement or standardized dosing guidelines.
Cooking, Heat, and How Much You Actually Get
Because S-methylmethionine is heat-sensitive, the way you prepare vegetables significantly affects how much of the compound survives to your plate. The tea data gives a vivid illustration: even the relatively gentle heat of drying tea leaves destroys a portion of the compound, and brewing in hot water degrades the majority of what remains.16PubMed. Formation of dimethyl sulfide from the decomposition of S-methylmethionine in tea (Camellia sinensis) during manufacturing process and infusion brewing Boiling, roasting, or stir-frying vegetables at high temperatures would be expected to have similar or greater effects, though detailed cooking-loss data for specific vegetables is sparse in the literature.
This is presumably why Cheney used raw cabbage juice in his original experiments rather than cooked cabbage or cabbage soup. If you are specifically trying to maximize your intake of S-methylmethionine from food, raw or minimally cooked preparations would be preferable. A raw spinach salad or lightly steamed broccoli would retain more than a long-simmered stew. That said, since no one has established a target intake for the compound, the practical significance of this is uncertain. You are not going to develop a deficiency from overcooking your greens.
Toxicity and Safety
One consistent finding across the available research is that S-methylmethionine has a low toxicity profile. Animal studies using therapeutic doses have not reported significant adverse effects, and its long history of use in over-the-counter gastric products in several countries without major safety signals offers some reassurance, though it does not substitute for formal safety trials at higher doses.17Research Journal of Pharmacy and Technology. Pharmacological effects of S-methylmethionine sulfonium chloride (vitamin U) The compound’s low toxicity, combined with its broad range of effects observed in preclinical models, is part of what keeps researchers interested. A pharmacologically active substance that also happens to be well-tolerated is a relatively rare combination, even if the clinical evidence trail remains thin.
For people who are simply eating a diet rich in leafy greens and cruciferous vegetables, there is no safety concern to speak of. The amounts of S-methylmethionine you would consume through food are modest and well within the range the body handles easily. The safety question becomes more relevant for concentrated supplements, where doses are higher and standardized human toxicity data is essentially absent from the Western medical literature. If you are considering a vitamin U supplement, the honest assessment is that it will probably not harm you, but the evidence that it will meaningfully help you is weaker than the marketing suggests.
The Supplement Market Versus the Science
Vitamin U supplements are widely available online and in health-food stores, typically marketed for digestive health, acid reflux, and sometimes skin repair. The gap between these marketing claims and the underlying evidence is considerable. Most of the stomach-protection research comes from animal models or Cheney-era human trials that would not meet current standards for clinical evidence. The skin and wound-healing data is almost entirely from cell cultures and rodent experiments. The organ-protection findings are exclusively from rats.
None of this means the compound is useless. It means we do not yet know whether the effects seen in animal models translate to humans at the doses present in supplements. A 2025 review characterized S-methylmethionine as a “promising candidate for the development of novel medicines” precisely because of its broad activity and low toxicity, but also emphasized the translational barriers that still need to be cleared.18Research Journal of Pharmacy and Technology. Pharmacological effects of S-methylmethionine sulfonium chloride (vitamin U) “Promising candidate” is scientific language for “interesting enough to keep studying,” not “ready for clinical use.”
If you are drawn to the idea of vitamin U for stomach issues, you might get more reliable benefit from simply eating more raw or lightly cooked leafy greens and cruciferous vegetables. These foods deliver S-methylmethionine alongside fiber, other phytochemicals, and established nutrients, all of which support gut health through well-documented pathways. The compound is one piece of a larger nutritional picture, and isolating it into a pill may or may not capture the same effect as eating the whole food.