It sounds a little like guessing the number of jellybeans in a large jar at the county fair, but sometimes science is like that. In 2013, a team of researchers from Greece, Italy, and Spain published research that tried to answer the mind-boggling question: How many cells are in the human body?
If you base your answer on the weight of an "average" man (70 kg) and know that the mean weight of a cell is 1 nanogram, you'll get a vastly different answer than if you calculated based on the average person's size and the mean volume of a cell (4 billionths of a cubic centimeter). If you calculate by volume, you'll get 15 trillion cells, whereas if you calculate by weight, you'll get 70 trillion cells.
Further complicating matters, cells come in different sizes and grow in different densities. Do you count bacteria, too? In the end, the researchers’ calculation was 37.2 trillion, which remains the scientific community's best guess to answer this complex question.
Give or take a trillion ...
- So how’d they get there? In a time-consuming process, the researchers came up with estimates for each organ and tissue, based on the cell type, volume, and density in each part of the body.
- There are around 200 cell types in the human body, including neurons, stem cells, and red and white blood cells.
- For example, they determined that there are 50 billion fat cells in the average body. Heart muscle, they determined, has 2 billion cells. Skin cells add another 35 billion cells. And so on.
- The researchers said that cell counts can help doctors identify problem areas. “Knowing the total cell number of the human body as well as of individual organs is important from a cultural, biological, medical, and comparative modeling point of view."
