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As an illustration of the importance of optimal nutrition for good health, Dr. Wentz often talks about the number of cells that our bodies must continually replace during its normal functioning. The aggregate numbers are enormous, and it's clear that adequate nutrition is critical for cell rebirth.
The total number of cells in the human body is estimated to be between 75 and 100 trillion, and through the normal wear and tear of living, billions of them must be regenerated every minute of the day and night. Perhaps even more impressive than the total number of cells replaced in a given time is the variety of locations and organs in our bodies that must regenerate cells steadily or on demand. Each organ has specific functions, which in turn requires different cells in varying amounts.
The Gastrointestinal Tract
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The entire
human gastrointestinal tract is about 15 feet long. Every inch, from the mouth
to the opposite end, is lined with trillions of epithelial cells, mucus, endocrine,
and columnar, that must be replaced on a regular basis.
The portion
of the gastrointestinal tract called the small intestine is about nine feet in
length. Inside, there is extensive folding of the intestinal surface, called the
mucosa. Extending from the surface of the mucosa are finger-like projections known
as villi. Finally, the surface of each villus is covered with a single layer of
epithelial cells whose surface membranes form small projections called microvilli.
Combining the surface area of the folded mucosa, villi, and microvilli all together
results in the small intestine having an area some 600 times compared to that
of a fiat-surfaced tube with the same length and diameter. That total surface
area is calculated to be about 300 square meters, the area of a tennis court.
In every inch of this 300 square meters of the intestines there are thousands of new epithelial cells continually replacing older cells. The old cells disintegrate and slough off into the interior of the intestines. An incredible 17 billion epithelial cells are replaced each day in this process, and the entire epithelial surface of the small intestine is replaced approximately every five days.
Blood Cells
There are more red
blood cells (RBCs), or erythrocytes, in the body than any other type of cell.
Normal human blood contains 5,500,000 RBCs per micro litre, and the average male
body contains five to six litres of blood. A simple calculation tells us that
we have many trillions of red blood cells circulating throughout the body. With
a life span of only 120 days, billions of RBCs must be replaced every day. Iron,
folic acid, and vitamin B 12, plus the necessary proteins and other constituents
must all be present for the body to make each one of these billions of new cells.
The white blood cells
(WBCs), or leukocytes, including neutrophils, lymphocytes, monocytes, basophils,
and eosinophils, are much less numerous, representing only about one percent of
the cells circulating in the bloodstream. The need for regeneration of WBCs varies
widely depending on the activity of the immune system and other factors, but the
daily production of each type of cell still numbers in the billions.
Also circulating in the blood stream are the platelets, which are critical for blood clotting. They are the remaining fragments of relatively large white blood cells called megakaryocytes. We don't have nearly as many platelets as RBCs in a given volume of blood, but their life span is no more than 10-12 days, so nearly the same amount must be produced each day.
Skin and Bone
The average
person has a surface area of skin of about 2.3 square meters (a little more in
men, a little less in women). We completely change our skin approximately every
27 days, which amounts to almost a thousand new skins in a lifetime. The individual
skin cells last about a week, continually being displaced by millions and billions
of new cells pushing up from the germinative layer under the epidermis.
We shed about 600,000 particles of skin each hour, which adds up to 1.5 pounds each year. By 70 years of age, we will have lost 105 pounds (48 kilograms) of skin, equal to about two-thirds of our adult body weight. As one of the most important nutrients for healthy skin, an adequate supply of vitamin A is needed every day.
Meanwhile, on the inside, our bones undergo a constant dismantling and rebuilding, a process that slows only in the elderly. In fact, the skeleton is completely renewed every two years, with those bones sustaining the most daily wear and tear demonstrating the highest rate of rebuilding. Calcium is the single most important component, but magnesium, boron, vitamin D, and silicon are all essential to the maintenance of healthy bones.
In addition to the normal rebuilding process, whenever we fracture a bone the body must undertake extensive mending, including the replacement of blood vessels severed or damaged by the fracture. Finally, the cartilage in the joints that connect and cushion the bones is also steadily worn down and replaced, especially if we are physically active.
Tissue Maintenance & Repair
Cells such as blood and skin cells are said to be labile: they multiply and replace
themselves steadily throughout life. Other types of cells do not multiply continuously,
but are capable of regeneration when necessary, such as when damage occurs. They
are called 'stable' cells. Bone is an example of tissue, which is
both labile
and stable.
Some organs suffer significant injury in the course of performing
their normal functions and large numbers of their cells must be replaced. The
best example of an organ with stable cells is the liver. In addition to its function
of manufacturing many vital substances, such as cholesterol and clotting proteins,
liver cells detoxify the body of harmful chemicals such as drugs and alcohol.
This detoxification process sometimes causes severe damage to the cells as they
sacrifice themselves to protect the body. It's not just coincidental that the
liver is the only internal organ able to regenerate large portions of itself.
There are many other instances when the body must repair itself by replacing cells. Internal organs such as the pancreas must occasionally regenerate cells, especially after inflammation. In addition, the lungs, constantly exposed to pollutants in the air drawn in during breathing, steadily shed old and damaged epithelial cells. Large numbers of white blood cells joins this cellular debris when we suffer from a cold or other microbial infection. Wound healing requires the interaction of several kinds of cells, and the rapid migration of newly developed epithelial cells into the traumatised area. Now we know that even the brain, once thought to never gain new cells after birth, can grow new cells, especially in the hippocampus, which is closely associated with learning.
Life Situations
Certain
circumstances or stages of life may also require the generation of large numbers
of new cells. In women of childbearing age, menstruation is when the endometrial
lining of the uterus decomposes, causing a discharge of cellular debris and blood.
The blood flow normally amounts to 50 to 150 ml of blood (1/4 to 1/2 cup), which
amounts to many billions of cells lost. Iron is the most important single nutrient
for replacing blood cells, but most of us need supplementation only rarely.
Then
there is the growth that we are aware of, our hair and nails. The nails of the
fingers and toes, which are compacted dead epithelial cells, grow at a rate of
1.5 to 2 cm each year. The average human grows 26 or 27 feet of hair in a lifetime.
Compound all of this cell regeneration with what developing children are doing
every minute, growing bones and muscles at what sometimes seems to be an alarming
rate, and your appreciation of the necessity for good nutrition grows accordingly.
One response might be: "No wonder I'm tired all the time! How can my body possibly
keep up?" Don't worry. Simply provide your cells with good nutrition, including
eating right and taking high quality nutritional supplements like the USANA Essentials,
as well as adequate exercise and rest. They will regenerate themselves as needed
without your even thinking about it.
CALCULATION NOTES
The exact
number of cells regenerated in a given time are not easy to find or calculate.
Assuming that we have 100 trillion (1012) cells in the body.
We know that
each day has 24 hours, 1,440 minutes, and 86,400 seconds, so: Regenerating 1 billion
cells per second = 86,400,000,000,000 or 86.4 trillion, 400 billion cells/day,
which amounts to nearly a complete renewal of the body every day - too high.
Regenerating 1 million cells per
second = 86,400,000,000, 86.4 billion, cells/day, or only about 0.01% of the body
-too low.
Thus, the rate of regeneration is somewhere between 1 million and 1 billion cells per second. Perhaps 10 million/sec, which would renew approximately one percent of the body per day?
One Set of numbers we have is for erythrocytes. Best & Taylor estimates: In adult males, 231 X 109 per day or 231 billion per day, 9.6 billion per hour, 160 million per minute, 2.6 million per second.
Since RBCs are the most numerous cells in the body, but don't turn over as quickly as others, we are not far off from our total of 10 million per second, as above.
As
vast as these numbers are, they pale before the estimate of numbers of individual
organisms that make up our normal flora (bacteria on our skin and in our gastrointestinal
tract), which is ten times the number of cells in our bodies. Which are multiplying
even faster.
