How Many Cells Are In The Human Body?

The question of how many cells make up the human body, doesn't seem difficult to answer with today's technology.

I started to research this topic, because I recently saw a video that claimed that the human body contained only between 70 to 90 billion cells. This was far from the estimate of 10 trillion cells that I had read a few years ago. The first estimate is less than one percent of the second estimate. Those numbers aren't even in the same ballpark! But these numbers even get a wider gap between the "educated guesses" below.

One of the reasons why this question should be answered, is that scientists are building sophisticated computer generated virtual models of organs, such as the lungs, the heart and other organs. If these models have ten times too many cells as do real organs, their virtual models will be way off.

Yes, it is easy enough to look through a microscope and count off certain types of cells. But this method isn’t practical either for an entire body. Researchers have to examine certain areas, estimate the weight and or the volume of the cells and then extrapolate.

Some cells are easy to count, but others, such as tangled neurons, are much more difficult. If you could count ten cells each second and counted them all, it would take more time than to count them all, than has elapsed in recorded human history.

For now, probably the best estimate is from a study published in Annals of Human Biology, entitled “An Estimation of the Number of Cells in the Human Body.”

The authors were a team of scientists from Italy, Greece and Spain. They were by no means the first people to attempt to answer this question.

They examined scientific journals and books from the past few centuries and found many estimates. But those estimates ranged from 5 billion to 200 million trillion cells. The funny thing is that practically none of scientists who offered those estimates, provided any explanation whatsoever, as to how they came up with their calculations.

One example of a calculated estimate is by average cellular weight. If the average weight of a cell is about 1 nanogram and an taking an adult weighing 70 kilograms, simple arithmetic would lead us to conclude that that individual is made up of about 70 trillion cells.

On the other hand, it’s also possible to do this calculation based on the volume of cells. The average volume of a mammal cell is estimated to be about 4 billionths of a cubic centimeter. By this estimate, an taking adult's volume, you might conclude that the human body contains about 15 trillion cells.

Making matters more complex, our bodies are composed of cells with various shapes, sizes and densities.

The study then set out to estimate the number of cells in the body, by breaking it down by organs and cell types, but didn't count our 2 - 3 pounds microbes, which could have added 100 trillion to the number.

They came up with an estimate for the total number of each kind of cell, for example, we have about 50 billion fat cells and 2 billion heart muscle cells.

Adding up all their numbers, the scientists came up with about 37.2 trillion cells. That seems like a good guess for now, but who knows what future scientists will think?

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