The microbiota in our intestines are connected to everything from arthritis to autism. Now scientists suggest that gut bacteria can even predict future health. Two recent studies have shown that our microbiome can explain many diseases better than genetics and even predict the risk of death over the next 15 years.
The microbiome is a better predictor of complex disorders than genetic data
The first study reviewed 47 research papers that examined the relationship between collective genomes of intestinal microbes and 13 general diseases. These include schizophrenia, hypertension and asthma - all are considered complicated conditions because they are caused by both environmental and genetic factors. They then compared these studies with 24 genome-wide association studies (GWA) that correlate specific human genetic variants with diseases.
In general, genetic signatures of intestinal microbes are 20% better able to identify an individual with a general disorder than genetic data. For example, the microbiota studies were 50% better than the GWA studies in predicting whether someone had colon cancer. An individual's own genetic profile was a better predictor only in one case, predicting if a person had type 1 diabetes.
Although the author of the study, Braden Tierney (Harvard Medical School), admits that the analysis is preliminary, the analysis of both human microbiome and genetics can be used to improve patients' quality of life. According to Tierney, the goal is to identify key markers in both genome groups that could help diagnose complex diseases.
At the moment however, it is difficult to compare between the prediction power of the two techniques. Scientists don't know as much about the microbiome as they do about gene function.
However, one of the advantages of the microbiome - based diagnosis is that it is affected by its environment. An individual’s diet and the amount of exercise, for example, affect the microbiota significantly. Thus, it may be the best predictor of diseases such as type 2 diabetes, which usually involves significant environmental factors.
Human microbiome and life expectancy
In the second study, researchers investigated the relationship between the human microbiome and longevity. The analysis was based on a study conducted in Finland, which since 1972 has collected data on the health of thousands of participants. In 2002, the subjects contributed stool samples, which were then sequenced 15 years later. The data shows that people with an abundance of Enterobacteriaceae, a family of potentially infectious bacteria including E. coli and salmonella, are 15% more likely to die within the next 15 years.
The observed association between E. coli bacteria and increased risk of death can be seen in Finland's both Eastern and Western populations, which have different genetic origins and lifestyles. This is an impressive research because such long-term studies are rare and difficult to reproduce.
What role does the microbiome play in human health?
Both studies, however, are not conclusive whether the microbiome is associated with disease and lifespan. It is possible that microbes somehow cause disease or reduce life expectancy. But it is also possible that they simply reflect what happens in the body at the time of observation. In any case, both scientists and doctors who want to help prevent and treat human diseases should pay close attention to human microbiota.
Tierney, B. T., He, Y., Church, G. M., Segal, E. J., Kostic, A. D., & Patel, C. J. (2020). The predictive power of the microbiome exceeds that of genome-wide association studies in the discrimination of complex human disease. bioRxiv, 2019-12.
Salosensaari, A., Laitinen, V., Havulinna, A. S., Meric, G., Cheng, S., Perola, M., ... & Long, T. (2020). Taxonomic Signatures of Long-Term Mortality Risk in Human Gut Microbiota. medRxiv, 2019-12.