The human body is a marvel of biological engineering, constantly renewing itself through the process of cell turnover. This natural process ensures the replacement of old, damaged, or dead cells with new ones, maintaining tissue integrity and overall health. The rate of cell turnover varies significantly across tissue types, influenced by their function, location, and exposure to environmental factors. Understanding these variations underscores the critical role of proper nutrition in supporting optimal cell regeneration and tissue health.
There are approximately 30 trillion (3 x 1012) cells in the human body – the reference person is a healthy male aged 20-30 years, at 70 kg in weight and 170 cm in height (ref). The average human body also harbors ~38 trillion bacteria (ref).
Of the 30 trillion cells in the body, 87% of those by number are erythrocytes (red blood cells), which are very small and have an average lifespan of 120 days.
In comparison, 72% of the total cellular mass is made up of fat and muscle cells, which are quite large.
The lifespan of cells in the human body varies widely, depending on the tissue type. These lifespans range from 3-5 days for cells of the gut lining to years or a lifetime for heart muscle cells and neurons.
Cell turnover
On a daily basis, our bodies replace about 330 billion cells. That’s an equivalent of 4 million cells per second. About 86% of these cells being replaced daily are red blood cells, and the majority of the remaining cells are in the gut.
These 330 billion cells represent a mass of 80 20 grams being replaced daily. About 40% of the cellular mass being replaced comes from red blood cells, due to the sheer volume of these small cells. Another 40% is made up of gut cells. Fat and muscle cells make up only 5% of cell turnover due to their long lifespans.
Specific tissues
Erythrocytes (Red blood cells)
Nearly 250 million red blood cells are produced daily in the human body, with a lifespan of 120 days, on average. There are believed to be hormonal and nutritional factors that influence this lifespan. For proper development, the most important nutrients for red blood cell production are iron, vitamin B12, and folic acid (ref).
Bone
Bone is constantly undergoing turnover, with action by osteoclasts that break down bone tissue and osteoblasts that lay down new bone. Approximately 10% of the skeleton is turned over per year (ref). It’s believed that loss of bone density (osteopenia and osteoporosis) occurs as a result of bone resorption outpacing bone production. Nutrients that are critical for bone formation include calcium, magnesium, vitamin D, vitamin A, vitamin B12, and protein (ref).
Muscle
Skeletal muscle can repair and regenerate over weeks to months following minor injuries. Heart muscle, however, has a turnover rate of 1% per year, reflecting much less regenerative capacity. Smooth muscle turnover is variable, depending on location.
Nervous tissue
The regenerative capacity of neurons is extremely limited, making them essentially irreplaceable. Thus, a spinal cord injury is devastating, as the impacted neurons will not regenerate. Minor peripheral nerve injuries, however, do demonstrate some regenerative capability.
Gut
The lining of the esophagus turns over every 9 days (ref), and the lining of the colon turns over every 3-4 days (ref). Given that the intestine is exposed to a myriad of insults from the environment, it’s believed that this rapid turnover minimizes the exposure of the gut lining to the harmful environment (ref).
Liver
Liver cells have a turnover time of 300 to 500 days.
Skin
Our skin is continuously being replaced by new tissue, with the entire epidermis being renewed every 45 days. Skin is also continuously exposed to potential harmful environmental agents, including friction, infection, chemicals, UV light, and mechanical damage.
Taste buds
The entire surface of the tongue, including all of our taste buds, is replaced every 10 days.
Cartilage
Cartilage, the surface lining of bones in joints, has an exceptionally long turnover time, on the order of decades, if at all.
Replacing cells
Just as parts of a car wear out over time (e.g. brakes, spark plugs, timing belt/chain, etc.), so do the cells that make up our bodies. Certain cells are exposed to environmental stresses be it chemical, mechanical, or other.
When it comes to nutrition, there is a constant obsession over calories – energy intake. One of the many problems with the focus on calories is that energy doesn’t provide the necessary substrates for cell turnover. Energy doesn’t build cells; we need nutrients to build new cells. Simply counting calories doesn’t ensure that one receives the necessary nutrients. Thus, nutrition should focus on obtaining the critical nutrients that are necessary for producing healthy, new cells.
The Role of Nutrition in Supporting Cell Turnover
Nutrients are important regulators of cellular proliferation, not just as fuel or building blocks, but also by regulating the production and function of important proteins necessary for the cell cycle. Both micronutrients (vitamins and minerals) and macronutrients (proteins and fats) are necessary for proper cell production. A diet rich in nutrient-dense real foods provides the necessary building blocks for these processes, promoting tissue health and resilience.
Real Foods for Optimal Nutrition
Nutrition should be focused on the most nutrient-dense foods available. Also, avoiding processed foods, which often lack essential nutrients and contain harmful additives, further enhances the body’s regenerative capacity.
