Human gut microbiota influences health. The authors of this study performed a genome-wide association study of the gut microbiota using cohorts from Germany (1). Controlling for diet and non-genetic parameters, the authors identified significant genome-wide associations for overall microbial variation, including the gene encoding the vitamin D receptor. The authors observe significant shifts in the microbiota, most notably several disease susceptibility genes and sterol metabolism pathway components. The authors conclude that non-genetic and genetic factors each account for 10% of the variation in gut microbiota, whereby individual effects are relatively small.