Medical Image from E.M.Unit, obtained through the Royal Free Hospital School of Medicine/Wellcome Trust Photo Library and available under Creative Commons licensing.
In a groundbreaking study published in the Annals of Human Biology, a team of scientists from Italy, Greece, and Spain have provided a more accurate estimate of the number of cells in the human body [1][2]. The study, titled "An Estimation of the Number of Cells in the Human Body," refines earlier approximations that suggested around 37 trillion cells.
The researchers scoured the scientific literature for details on the volume and density of cells in various tissues such as gallbladders, knee joints, intestines, and bone marrow. They found that while many scientists offered estimates, few provided an explanation for how they arrived at these numbers.
The authors of the study note that the very fact that 34 trillion cells can cooperate for decades to form a single human body is amazing, and understanding the collective on a deep level is crucial to understanding multicellularity. They estimate that the human body typically contains about 30 trillion cells on average, with more specific estimates being around 36 trillion cells in males and 28 trillion cells in females.
The variation in cell counts between males and females is influenced by differences in body size and composition. For an adult man weighing 70 kilograms, simple arithmetic might lead to a conclusion of 70 trillion cells. However, the mean volume of a mammal cell is estimated to be 4 billionths of a cubic centimeter. Based on an adult man's typical volume, the human body might contain 15 trillion cells.
The scientists came up with estimates for the total number of each type of cell, such as 50 billion fat cells and 2 billion heart muscle cells. Adding up all their numbers, they estimated that there are 37.2 trillion cells in the human body.
The number of cells in an organ has bearing on some medical conditions, such as cirrhosis of the liver, where the diseased organ may have as few as 172 billion cells. The study's authors see their estimate as an opportunity for a collaboration to zero in on a better estimate, potentially through an online database assembled by many experts on many different body parts.
The study published in the Annals of Human Biology provides a comprehensive and updated estimate that is widely accepted among biologists and human physiologists [1][2]. The common estimate of a trillion cells in the human body is wrong, as demonstrated by the new research. For instance, the density of red blood cells in a beaker of blood is much higher than the density of skin cells, leading to a staggering estimate of 724 trillion cells if using their density to estimate the cells in a human body, and a paltry estimate of 35 billion cells if using skin cells' density.
The evolution of even a basic level of multicellularity is remarkable, and our ancestors went beyond a simple sponge-like anatomy, evolving a vast collective made of many different types. Understanding this collective on a deep level is crucial to understanding multicellularity and human biology as a whole.
References: [1] Bianconi, A., et al. (2013). An estimation of the number of cells in the human body. Annals of Human Biology, 40(5), 465-470. [2] Annals of Human Biology. (2021). An Estimation of the Number of Cells in the Human Body. Retrieved from https://onlinelibrary.wiley.com/doi/abs/10.3109/03014460.2013.775388
- The study's authors advocate for further research to refine the estimate of the number of cells in the human body, suggesting a potential collaboration using an online database.
- The research team estimates that the human body on average contains approximately 30 trillion cells, with more specific estimates for males (36 trillion) and females (28 trillion) due to differences in body size and composition.
- The evolution of multicellularity in human biology is a subject of great curiosity and importance, as understanding the collective of distinct cell types is crucial for grasping the foundation of human health, wellness, and the impacts on medical conditions like cirrhosis of the liver.
