So, what is the relationship between antioxidants and aging?
Promotion of antioxidant foods (Source: Weibo)
There is an intermediate link between antioxidants and aging called free radicals.
Free radicals can be simply understood as highly active groups. Oxygen is a free radical. [ 1]
Ideally, oxygen entering the human body should be fully utilized by cells. Unfortunately, in reality, there are always some oxygen molecules that will escape. When an idle oxygen molecule meets a normal cell structure, it is inevitable that there will be contradictions.
For example, the genetic material of cells is hidden in the nucleus. According to the molecular orbital theory, electrons are stable only when they are paired, while in oxygen molecules, two unpaired electrons are unstable. When unstable oxygen molecules meet the originally stable genetic material, they will take away the electrons of the genetic material. In this way, the oxygen molecule is stable, but the genetic material is destroyed.
Schematic diagram of free radical reaction (picture from network)
Damage to genetic material may lead to diseases, such as cancer and cardiovascular diseases, on the other hand, it will affect the life span of cells. The human body is composed of cells, and human health depends on the state of cells in the final analysis. Therefore, in the 1950s, some scholars put forward the free radical theory of aging. [2]
According to this theory, after oxygen enters the human body, it will interact with respiratory enzymes to generate more active free radicals, such as carboxyl groups, which will destroy genetic material and affect the metabolism and regeneration ability of cells. Therefore, scholars speculate that reducing free radicals in the human body can greatly delay aging and prolong life.
Subsequent research confirmed this statement. In 1990s, some scholars transplanted two kinds of enzymes that can reduce free radicals into Drosophila melanogaster. As a result, the average life span of fruit flies has increased by one third. [3]
For humans, it is not possible to increase the number of some enzymes directionally at present, but we can reduce the production of free radicals by supplementing antioxidants, such as vitamin C, so we get such a theory.
Supplementing antioxidants → reducing free radicals → reducing cell damage → reducing diseases and prolonging life.
There seems to be no problem, however, there are many signs that this will not work.
First of all, can taking vitamin C really reduce the formation of free radicals?
Vitamin C itself is a highly oxidizable substance. When free radicals meet vitamin C, they will react with vitamin C. Vitamin C consumes free radicals and normal substances are protected. Therefore, in theory, vitamin C is a good antioxidant.
The reality is intriguing. Some scholars ask volunteers to drink 750 ml of cranberry juice every day. 100g cranberry juice contains 9.3mg vitamin C, which is stronger than apple, so it is not prominent. However, besides vitamin C, cranberry juice also contains many antioxidants, such as vitamin A and vitamin B. ..
It stands to reason that the antioxidant status of volunteer cells and the oxidative damage of genetic material should be reduced. However, cranberry juice did not show such an effect. [4]
Vitamin content of cranberry juice (source: USDA)
If the above experiment can be explained by "insufficient antioxidant content in cranberry juice", then the following research is the beginning of trouble.
Many large-scale surveys show that increasing the intake of vegetables and fruits can reduce the incidence of cancer. If the free radical theory is applied, it is easy to explain that vegetables and fruits contain antioxidants. However, in most prospective experiments, vitamin C did not show the effect of reducing the incidence of cancer.
A study pointed out that taking a high dose of vitamin C (65 65,438+0.20 mg) can reduce the incidence of cancer in men, but it is ineffective in women. Both men and women have free radicals, which is inconsistent with the theory. Why are there gender differences? [5]
Linxian County, Henan Province is a high incidence area of esophageal cancer in China. From 1984, the Cancer Institute of China Academy of Medical Sciences cooperated with the National Cancer Institute of the United States, and conducted nutrition intervention experiments there for more than ten years. The results showed that vitamin C supplementation was not helpful to prevent esophageal cancer. Strangely, selenium (another antioxidant) shows the effect of reducing cancer. [6]
But this does not mean that we should supplement selenium for health, but the mechanism of interaction between antioxidants and free radicals needs further study.
In addition, many people think that vitamin C can improve immunity, and it is always harmless to eat more.
A certain amount of vitamin C is of great significance for maintaining the function of white blood cells and promoting the formation of antibodies. However, many large-scale surveys show that as long as vitamin C is not lacking, no matter how it is supplemented, it can not reduce the probability of catching a cold, nor can it alleviate the symptoms of a cold, and at most it can shorten the period of catching a cold. [7]
The Nutrition Society of China suggests that adults should take 85mg of vitamin C,100g of red pepper or a kiwi fruit, or half a cauliflower every day, without additional supplementation.
Vitamin C content in common foods, unit: mg/ 100g (image source: China residents' dietary nutrient reference intake (version 20 13)).
Of course, the toxicity of vitamin C is very low, and the maximum tolerance for adults exceeds 65,438+000 mg. If you don't eat vitamin tablets as a meal, you don't have to worry about poisoning. Other antioxidants are not so harmless.
Some scholars analyzed 78 random experiments involving 300,000 people. The results showed that vitamin E, β -carotene and high-dose vitamin A could increase the mortality slightly. [8]
In a study published last year, 77,000 people were followed up for 10 years. The results show that the incidence of lung cancer will double when taking large doses of vitamin B (B6 20 mg of B6 daily and 0.255 mg of B6 5438+ daily). For smokers, it is even more terrible, and the incidence of lung cancer will increase by three to four times. [9]
Why is this happening?
It may be because the human body has a set of methods to fight free radicals. As mentioned earlier, there are two kinds of enzymes in human body, superoxide dismutase (SOD) can convert free radicals into hydrogen peroxide, which is also commonly known as hydrogen peroxide. Trace hydrogen peroxide has a certain physiological function, which can kill invading bacteria through its strong oxidation.
After that, catalase will take over and further convert excess hydrogen peroxide into oxygen and water. [10] On average, the genetic material of cells is attacked by more than 10000 free radicals every day, because these two enzymes are healthy for most people.
On the other hand, additional antioxidants may produce some harmful substances when they react with free radicals, or appear in reactions unrelated to free radicals, such as β-carotene, which may affect the immune system. [ 1 1]
In short, although the relationship between free radicals and aging and diseases is becoming more and more clear, there are still some mysteries to be clarified; According to the existing research, a large number of antioxidants are not good for health.
If you really care about free radicals, you can try to quit smoking first. When tobacco burns, it will produce a lot of free radicals.
Free radical theory (support source: Wikipedia)
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refer to
[1] Road protection. Oxygen free radicals and natural antioxidants [M]. Science Press, 2002.
Harraan D. Aging: A Theory Based on Free Radical and Radiochemistry [J]. 1955.
[3] free radical aging [EB/OL]. [20 18-09-28]. The signed articles published on this website only represent the author's views and have nothing to do with this website. If there is any infringement, you are responsible.
Author: Zhao Yanchang