Methylamine in Human Urine

Background: Methylamine is the simplest aliphatic amine found in human urine. In the body it is thought to play a significant part in central nervous system disturbances observed during renal and hepatic disease and also has a role in general toxicity caused by oxidative stress. The present study provides data on the daily urinary excretion of methylamine in a population of unrelated healthy volunteers and investigates a variety of food substances as potential dietary sources.

Methods: Complete 0-24 h urine samples were collected from 203 volunteers (102 male, age 22.2 +/- 4.5 years, mean +/- S.D.; 101 female, age 21.6 +/- 5.0 years) maintained on their normal diets. Six male subjects also consumed, on different occasions separated by at least 1 week, 41 foods and collected the subsequent 0-8 h urine. In addition, these subjects also ingested various dietary precursors (betaine, carnitine, choline, creatinine, lecithin) and collected the following 0-3 day urine. All urine samples were analysed for their methylamine content.

Results: The average daily output of methylamine was 11.00 +/- 8.17 mg (12.73 +/- 9.35 male; 9.27 +/- 6.35 female) with a range of values spreading from 1.68 to 62.30 mg. Dietary studies suggested that certain fish and seafoods (clam, crab, haddock, halibut, octopus, tuna) and fruit and vegetables (pear, peas, tomato) may add to this urinary output. Ingestion of creatinine also increased urinary methylamine levels.

Conclusions: For the first time, standard daily excretion values for methylamine have been established for a large population. Chemical and dietary precursor studies indicated that there was no major exogenous source of this amine and suggested that the origin of the majority of human urinary methylamine is endogenous with only subtle contributions from the diet.