Revised estimates for the number of human and bacteria cells in the body

We critically revisit the “common knowledge” that bacteria outnumber human cells by a ratio of at least 10:1 in the human body. We found the total number of bacteria in the “reference man” to be 3.9·10 13 , with an uncertainty (SEM) of 25%, and a variation over the population (CV) of 52%. For human cells we identify the dominant role of the hematopoietic lineage to the total count of body cells (≈90%), and revise past estimates to reach a total of 3.0·10 13 human cells in the 70 kg “reference man” with 2% uncertainty and 14% CV. Our analysis updates the widely-cited 10:1 ratio, showing that the number of bacteria in our bodies is actually of the same order as the number of human cells. Indeed, the numbers are…

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  Leona M. and Harry B. Helmsley Charitable Trust