[Kim Jaeho's Story of Life]<182> Life Striving to Maintain Homeostasis

Many people around us believe that certain foods or substances are especially good for the body. Foods considered beneficial often become trendy for a while, only to be replaced by other foods at some point, and even those trends do not last long. Records show that Qin Shi Huang, who unified China over 2,200 years ago, sent people to eastern countries in search of an elixir of immortality. Nowadays, as the novel coronavirus disease (COVID-19) spreads rapidly, there are also talks about consuming a lot of salt, turmeric, and vitamin C.

If there are good foods or substances, is it better to consume more of them? In biology, the characteristic of all living organisms to maintain internal stability in aspects such as body temperature, sodium concentration, blood sugar, and hydrogen ion concentration (pH) in response to changes in the external environment is called “homeostasis.” Failure to maintain homeostasis within an acceptable range leads to illness, and in severe cases, death.

For example, consider the claim that eating a lot of salt to maintain a 0.9% salt concentration in the body can help overcome COVID-19. When sodium concentration rises above the appropriate level due to high salt intake, our body expels sodium ions through urine via the kidneys, and when sodium concentration drops, it reabsorbs sodium ions to maintain the proper sodium level in the blood. If sodium concentration is not well regulated and becomes too high, it results in hypernatremia; if too low, hyponatremia occurs.

It might be easy to think that eating a lot of salt is not a problem because excess salt is expelled through urine, but many studies show that when the kidneys excrete salt, calcium is also lost, which can cause osteoporosis, and it is also a cause of hypertension and stomach cancer. For these reasons, the World Health Organization (WHO) and professional organizations recommend limiting daily salt intake to about 5 grams.

When body temperature rises above the appropriate level, temperature receptors in the hypothalamus of the brain detect this and send signals to sweat glands in the skin to secrete sweat. As sweat evaporates, it cools the skin and lowers internal body temperature, and blood vessels dilate to increase blood flow to the skin, cooling the body. When body temperature drops, blood vessels constrict to reduce blood flow to the skin, retaining heat inside the body, and muscles, organs, and the brain produce heat in various ways to raise body temperature.

Blood sugar, used as fuel by all cells, rises when glucose is absorbed in the small intestine and falls when used by cells, but it is managed within an appropriate range. When blood sugar rises, the pancreas secretes insulin into the bloodstream, which converts glucose into glycogen in the liver, stores glucose as triglycerides in fat cells, and converts glucose into glycogen in muscle cells. When blood sugar falls, the pancreas secretes glucagon, which converts glycogen in the liver and muscles back into glucose to raise blood sugar levels.

Ionized calcium in the blood, involved in many enzyme activities and physiological processes, is strictly regulated by the thyroid and parathyroid glands. When ionized calcium concentration is too high, the thyroid secretes hormones that store calcium in the bones in a water-insoluble form, and when it is too low, the parathyroid secretes hormones that use calcium from bones to raise blood calcium levels to maintain the appropriate level.

The hydrogen ion concentration (pH) of the blood indicates its acidity or alkalinity, and the body maintains a slightly alkaline pH around 7.4 as the appropriate level. If pH rises causing alkalosis or falls causing acidosis, the body adjusts the partial pressure of carbon dioxide during respiration or excretes hydrogen ions or bicarbonate ions through the kidneys to maintain pH at the proper level.

Using appetite to match the amount of energy consumed through food with the amount of energy used is to maintain energy homeostasis. When energy intake is needed, the hormone ghrelin is secreted to stimulate appetite, and when energy intake should stop, the hormone leptin is secreted to induce a feeling of fullness.

In addition, the body maintains appropriate levels of all substances necessary for health, such as iron, copper, potassium, oxygen, carbon dioxide, and water content.

The message homeostasis gives us is clear: nothing is better in excess, and maintaining appropriate levels is the way to preserve life. The same applies to food. Even substances that are essential must be expelled from the body if they exceed appropriate levels, which can be harmful. This is why food guidelines in the United States and Europe recommend limiting intake of sugar, saturated fats, trans fats, salt, and alcohol.

Kim Jae-ho, Independent Researcher