Researchers discover a link between human blood cholesterol levels and a gene in the microbiome that could one day help people manage their cholesterol through diet, probiotics, or entirely new types of treatment.

Many species are known, like E. coli, but many more, sometimes referred to as «microbial dark matter,» remain elusive. «We know it’s there,» said Doug Kenny, a Ph.D. candidate in the Graduate School of Arts and Sciences, «because of how it affects things around it.» Kenny is co-first author on a new study in Cell Host and Microbe that illuminates a bit of that microbial dark matter: a species of gut bacteria that can affect cholesterol levels in humans.

«The metabolism of cholesterol by these microbes may play an important role in reducing both intestinal and blood serum cholesterol concentrations, directly impacting human health,» said Emily Balskus, professor of chemistry and chemical biology at Harvard University and co-senior author with Ramnik Xavier, , core member at the Broad, co-director of the Center for informatics and therapeutics at MIT and investigator at Massachusetts General Hospital. The newly discovered bacteria could one day help people manage their cholesterol levels through diet, probiotics, or novel treatments based on individual microbiomes.

According to the Centers for Disease Control and Prevention (CDC), in 2016, over 12 percent of adults in the United States age 20 and older had high cholesterol levels, a risk factor for the country’s number one cause of death: heart disease. Only half of that group take medications like statins to manage their cholesterol levels; while such drugs are a valuable tool, they don’t work for all patients and, though rare, can have concerning side effects.

«We’re not looking for the silver bullet to solve cardiovascular disease,» Kenny said, «but there’s this other organ, the microbiome, another system at play that could be regulating cholesterol levels that we haven’t thought about yet.»

The hog sewage lagoon

Since the late 1800s, scientists knew that something was happening to cholesterol in the gut. Over decades, work inched closer to an answer. One study even found evidence of cholesterol-consuming bacteria living in a hog sewage lagoon. But those microbes preferred to live in hogs, not humans.

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Materials provided by Harvard University. Original written by Caitlin McDermott-Murphy. Note: Content may be edited for style and length.