Summary - Hospitalized peptic ulcer patients were cured by drinking cabbage juice containing 42-162 mg of Vitamin U per day for 7-10 days when eating a bland diet and getting bed rest.
A recommended dietary allowance (RDA) for Vitamin U has not been established by the US National Academy of Medicine. However, an estimate of how much Vitamin U you could try can be made by calculating the amount of Vitamin U used in Dr Cheney's studies. Cheney healed ulcer patients with 1 liter of cabbage juice per day over 7-10 days. At the time, Cheney didn't know exactly how much Vitamin U was in the juice. He just knew this much juice in combination with a bland diet and rest was enough. In more recent years, Vitamin U was identified as S-methylmethionine, and there have been several studies in which the amount of this amino acid has been quantified in cabbages. From these studies we can approximate how much supplemental Vitamin U is required to heal ulcers.
In 2003, Kim reported 26-46 mg/100 g of dry weight, which given that a cabbage is ~92% water, works out as 21-37 mg/kg of fresh cabbage. In 2009, Scherb and others found that cabbages have 81 mg of Vitamin U per kg of fresh cabbage. In 2017, Song et al determined that cabbages contain 50 mg/kg of Vitamin U. So we can estimate that there is roughly 21-81 mg Vitamin U per kg of cabbage.
Why this variation? There are several probable explanations. One possibility is that different parts of the cabbage were analyzed by the various researchers. Kim found that the concentration of Vitamin U in the core, middle and outside leaves varied by 2-fold, with the middle leaves having the most. Scherb found that vegetables grown in different countries had different amounts of Vitamin U, suggesting that some of the variation may be due to geography. Another possibility is that the cabbages were not all of equal freshness or picked at the same time of the year. In an older study, Kovatscheva and Popova noted that cabbages lose 62% of their Vitamin U during six months of storage without refrigeration and 34% with refrigeration. Cabbages harvested in spring /summer have the highest Vitamin U content. Finally, it is possible that the various extraction procedures used in the studies resulted in slightly different yields of Vitamin U.
1 liter of juice is typically extracted from about 2 kg of cabbage. Cheney arrived at 1 liter from prior studies in which various volumes of cabbage juice were given to guinea pigs subjected to chemically-induced ulceration. 100% of the guinea pigs responded to the guinea-pig equivalent of 720 ml of juice. The volume used in the clinical study was rounded up to 1 liter to take into consideration variations in body weight and unexpected factors.
Taking all this data together, it can be estimated that 1 litre of juice contains 42-162 mg of Vitamin U, which probably represents a maximum daily requirement.