A key factor for aging is reactive oxygen species

Japan is the aged society without parallel in the world. As of 2021, the percentage of the population aged 65 or older in Japan was 29.1%, which exceeds the level of an aging society (7%), that of an aged society (14%), and even that of a super aged society (21%).

Of course, it is welcoming that people enjoy longevity. On the other hand, however, the aging rate of Japan continues to rise owing to the acceleration of a declining birthrate. Consequently, social security burdens have become a big issue.

That induces us to put more value on extending healthy life expectancy, not just longevity.

Healthy life expectancy refers to the period during which a person can live independently without the need for nursing care and so forth. In fact, Japan has not only the highest average life expectancy but also the highest healthy life expectancy in the world.

Still, as of 2019, the expected lifetime after a person’s healthy years were over was 8.73 years for men, and 12.07 years for women. In other words, we will have about 10 years when we cannot live independently and need support such as nursing care.

It is significant to shorten this period as much as possible in terms of social security, but above all, it is also very critical in terms of maintaining the quality of life (QOL) or allowing us to live in good health.

So, what can we do to maintain and improve our health in order to extend healthy life expectancy? As is commonly known, it is self-evident that regulating the rhythm of everyday life, avoiding overeating, overdrinking, and smoking, trying to eat a well-balanced diet, and doing moderate exercise are good for extending healthy life expectancy.

Despite these efforts, however, senescence progresses with aging. This is because the working of our body’s cells deteriorates, and their function gets weaker than it used to be when we were young. Reactive oxygen species are considered as one of the causes of the progress of senescence.

In ordinary oxygen, one of its six outer electrons around an oxygen nucleus is paired with a similar electron around another oxygen nucleus. It is called triplet oxygen, which is a stable condition. We take this oxygen into our body and use it to produce energy to survive.

However, as the oxygen is used in our body, it can lose the balance of electrons, causing it to become unstable. That is reactive oxygen species.

Reactive oxygen species can be divided into various types depending on how the balance of electrons is lost. There are four types of reactive oxygen species generated in the human body: singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radical.

As these reactive oxygen species are unstable, they steal electrons from surrounding molecules to become stable. This is called reactivity, and to show strong reactivity is called high activity.

Although activity sounds like a good thing, in short, reactive oxygen species attack surrounding cells.

When highly reactive oxygen species attack cells in this way, the cells and their genes are damaged and unable to perform their function properly. This manifests as the aging phenomenon, and is considered to induce cancer, arteriosclerosis, and diminished immune function.

Carotenoid that scavenges reactive oxygen species

So, is it possible to curb reactive oxygen species? Actually, our body has an antioxidant defense mechanism that prevents excess accumulation of reactive oxygen species. This is an endogenous antioxidant enzyme that scavenges reactive oxygen species.

However, this endogenous antioxidant enzyme is less likely to be generated with aging. In short, reactive oxygen species are likely to accumulate in our body with aging.

Consequently, it is effective to take substances that compensate for the decline of endogenous antioxidant enzymes. These substances are called exogenous antioxidant enzymes, one of which is carotenoid.

Carotenoids are natural pigments of red, orange, and yellow that are widely distributed in microorganisms, algae, plants, and animals. In general, lycopene, found in tomatoes, and β-carotene, found in carrots, are well-known examples of carotenoids.

Animals, including humans, cannot synthesize carotenoids in their own bodies, but they can ingest carotenoids produced by plants.

For example, salmon cannot biosynthesize carotenoids by itself, but by taking in carotenoids derived from phytoplankton, its flesh turns into a beautiful orange color called salmon red.

Carotenoids have a strong antioxidant effect on singlet oxygen. Carotenoids receive energy from the unstable singlet oxygen and liberate it as heat.

The singlet oxygen that lost energy returns to a stable triplet state. In short, highly activated reactive oxygen species in an unstable state return to normal oxygen in a stable state. This is called scavenging of reactive oxygen species.

The general structure of carotenoids consists of two main parts. The combination of these two parts allows the existence of many structures. Presently, more than 750 types of natural carotenoids have been reported.

Carotenoids need to have a certain structure to show a significant scavenging activity against singlet oxygen, and the strength of the scavenging activity depends on the structure. It is also known that carotenoids with a strong red color have a stronger scavenging activity against singlet oxygen.

These results indicate that carotenoids could be used more effectively by understanding the characteristics of various carotenoids.

Maintaining balance is key

I have been searching for carotenoids with stronger antioxidant activity through my study of microorganisms.

In fact, it is thought that only a few percent of all microorganisms on Earth have been discovered by humans so far. Thus, we can assume that many microorganisms that produce not only carotenoids but also substances useful to humans still exist on Earth.

I believe that the discovery of useful functional substances from unknown microorganisms could help maintain and improve our health.

As I mentioned before, in Japan, where we already enjoy longevity, there is no doubt that extending healthy life expectancy is very beneficial for both individuals and society.

On the other hand, when some healthy foods or substances are featured in the mass media, the number of people who exclusively consume excessive amounts of such foods and substances is growing. However, this may be ineffective or even counterproductive.

For instance, it is true that vitamin C is good for your health, but it is not true that the more you eat, the better. What cannot be used up in your body is discharged as it is. In short, just because you take it a lot of something, it does not mean it will be more effective.

Reactive oxygen species are not merely harmful.

For example, superoxide and hydrogen peroxide, which are generated from white blood cells, are known to be involved in our immune function and defense mechanism against infection. In addition, it has been revealed that they are used for signal transduction between cells as well as cell differentiation.

Instead of the easy way of thinking that reactive oxygen species are harmful and should be eliminated by all means, it is important to maintain a balance between the production of reactive oxygen species and the antioxidant defense mechanism by compensating for the declining antioxidant capacity caused by aging and reducing the opportunities for unnecessary generation of reactive oxygen species.

I think utilizing functional substances such as carotenoids for this purpose will be one of the beneficial things for our body. This will lead to maintaining and promoting our health and extending healthy life expectancy.

In this sense, it is important for maintaining and improving QOL to work on maintaining balance, not being overly biased.

Moderate eating habits are of course important, but if you make them too strict, it can accumulate mental stress. I believe it is good to eat what you like and enjoy drinking sometimes. Excessive exercise will damage your body and accelerate the aging of cells.

I encourage you to try to always gain this kind of knowledge and do what is truly good for your body.

* The information contained herein is current as of July 2022.
* The contents of articles on Meiji.net are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.

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