Our cells have been counted
How many cells are there in a person
Kirill Stasevich, "Science and Life" based on Science News: Body's bacteria don't outnumber human cells so much after allWhen it comes to the gastrointestinal microflora, it is often possible to hear that the number of bacterial cells living in our digestive tract is 10 times greater than the number of cells that make up our body.
The ratio is certainly impressive – it immediately becomes clear how many bacteria we have and what a big role they play in our lives.
Percentages of different cells in the human body.
(Illustration by R. Sender, S. Fuchs and R. Milo /bioRov.org 2016.)
The ratio "10 to 1" is quite old, it has been recognized by all biologists for a long time (and some even said that it is actually even more, that microbes outnumber our own cells by 100 times). However, recently experts are increasingly saying that the proportion is greatly exaggerated, and that it needs to be revised. For example, according to the American Microbiological Society, the actual ratio corresponds to only three bacterial cells per one human. And in 2014, Judah Rosner from the National Institute of Diabetes and Kidney and Digestive System Diseases, in his letter to Microbe magazine, generally spoke out in the sense that the notorious "10 to 1" is not true, and the popularity of these figures speaks only about the love of researchers for round numbers.
Researchers from the Weizmann Institute undertook to accurately recalculate the ill-fated proportion again. In the article Revised estimates for the number of human and bacterial cells in the body, published on the website bioRxiv.org the authors of the paper write that the "average" human body weighing 70 kg contains about 30 trillion of its own cells and about 40 trillion of bacteria, that is, the ratio is approximately 1.3 to 1 – a striking difference from the previous tenfold the predominance of microbes. The estimate of bacteria allows for a 25% deviation, that is, there may be 30 trillion or 50 trillion of them, but it does not reach "10 to 1" in any case.
In the work of Ron Sender and his colleagues, you can find other amazing figures. For example, the most numerous cells of our body were red blood cells: they account for 84%. On the other hand, if we count by weight, then muscles and fat lead here – they account for 75% of body weight, but muscle and fat cells are quite large and therefore make up only 0.1% (!) of the total cell number. Of course, do not forget that everything is calculated here for the "average human body weighing 70 kg", and, for example, for women whose blood volume is less, the ratio between body cells and bacteria will shift by about a third in favor of the latter, and in growing children the proportion of bacteria will naturally decrease. But with obesity, the cellular proportion does not change too much (which is understandable if you remember that fat cells together with muscle cells are a minority).
The cells were recalculated based on the data available to date, so in the future, when rechecking the ratio, experimental methods of the "cell population census" will most likely be used. Some experts in their reviews of the above work pointed out that only bacteria were taken into account here, but archaea, fungi, viruses and other microorganisms also live in us and on us; and if we take into account, for example, viruses that outnumber bacteria, then the ratio is "1.3 microorganisms per one the human cell" will clearly shift in favor of the microbiome. As for how, from a practical point of view, it is necessary to find out the full balance between body cells and microbes, opinions may differ here, and many believe that it is certainly interesting to know the total figure here, but it is useless. However, one important benefit should be pointed out here: when you want to refer to some well-known information that you learned more than a dozen years ago (especially if the information is of a medical or near-medical nature), it is useful to ask what modern science thinks about this.
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13.01.2015