Is human methane production affected by long-term occupational exposure to a methanogenic flora?

The factors determining human methane production or nonproduction are unknown. Exposure at a young age to a methanogenic flora is thought to be of significance. We examined whether long-term occupational exposure to methanogenic flora in adult life affects methane production. Among 38 subjects who worked in a cowshed for a mean period of 14 +/- 15 years, the proportion of methane producers was identical to that found in well-matched controls. The length of work in the cowshed had no effect on methane production.