I. Why does skin age?

When it comes to aging, many people immediately think of free radicals, oxidation and so on, but few people think of how much the close proximity of sunlight affects the aging of the human body; in fact, photoaging is even more frightening than natural aging!

It is an obvious fact of life that skin exposed to sunlight (e.g. face, neck, forearms, etc.) is more prone to wrinkles, pigmentation, roughness, loss of elasticity, and other symptoms of skin aging. There is a special term for this phenomenon - photoaging.

"Light aging", that is, after chronic exposure of the skin to sunlight or other sources of radiation, a series of premature aging phenomena and lesions. Appearance is manifested as skin laxity, hypertrophy, deep and coarse wrinkles, some people in the neck can be seen in the diamond-shaped skin, there are local pigmentation as well as capillary dilatation, these are the results of long-term radiation in nature. Because of this, those long-term outdoor activities or living in the plateau, seaside people, the appearance often looks more than their peers show "weathered".

Skin is the first line of defence of the organism, playing an important role in resisting various external aggressions, maintaining the homeostasis of the internal environment and safeguarding the physiological functions of the organism.

Skin ageing is affected by both intrinsic and extrinsic factors, one type of ageing is endogenous or chronological ageing is mainly determined by genetic factors and is an inevitable process. As a result of ageing, the metabolism of cells in the body declines, leading to natural skin ageing. The other type of skin ageing is due to external environmental factors. Among them, photoaging is the most dominant form of external skin aging, accounting for more than 80% of facial aging.

II.The main culprit of photoaging is UV rays

Often, the most immediate experience of exposure to the sun is a tan, with ultraviolet (UV) rays behind the scenes. However, UV rays have an intricate effect on human health that goes far beyond just tanning. Tanning is actually a protective measure of the skin against UV damage. Epidermal melanin protects the skin by preventing UV rays from penetrating the skin. What we should really be concerned about are the many skin health problems caused by UV rays, and the "photoaging" of the skin that almost everyone can't escape.

UVA and UVB emitted by the sun play different roles:

1. UVB from the sun

UVB irradiation induces the degradation of collagen in the skin's basement, causing damage to the basement membrane structure, which is the structural foundation that connects the epidermis to the dermis and maintains the skin's surface flatness and barrier function. Its damage leads to an interruption of the skin's mechanical stability, making it susceptible to the formation of wrinkles.

2. UVA from the sun

UVA, due to its strong penetrating power, directly attacks the dermis, generating a large number of reactive oxygen radicals in the skin, which, after a number of links, ultimately inhibit collagen synthesis and cause sustained oxidative damage to dermal proteins, leading to cross-linking, denaturation, and doughnut accumulation of collagen and elastin, resulting in skin laxity and the appearance of coarse and deep wrinkles.

Long-term ultraviolet radiation can cause oxidative stress, inflammatory response, immune response and apoptosis of skin cells. Skin photo-aging occurs in the core link is the ultraviolet radiation caused by increased production of reactive oxygen species, cellular metabolic changes produce excessive reactive oxygen species, resulting in an imbalance in the body's oxidation and antioxidant system, causing skin tissue photodamage, acute photodamage can be manifested as erythema, swelling, dryness, flaking and so on.

Chronic photodamage, i.e. photoaging, can be manifested as skin roughness, thickening, atrophy, wrinkle formation, pigmentation and cancer.

Unlike the natural ageing of the skin, which begins in adulthood, photo-ageing of the skin begins in childhood and progresses gradually. It can be said that UV damage to the skin is cumulative, and with each unprotected contact with the sun, the skin takes a further step towards ageing.

Photoaging is more common in fair-skinned people. In an Australian study of participants under the age of 30, 72 per cent of men and 47 per cent of women showed moderate to severe photoaging. In people with darker skin tones, wrinkles were not visible until age 50 due to the protective effect of melanin.

And another study found gender differences in UVB-induced skin carcinogenesis, inflammation and DNA damage. After prolonged exposure to equal doses of UVB, male mice developed tumours earlier and had more and larger tumours than female mice. In other words, men are more likely to develop oxidative DNA damage in the skin and have a higher risk of skin cancer than women in the same UV environment. Men who don't like sunscreen should beware.

III. Two scientific studies confirm that NMN can repair photoaging damage

As UVB-induced changes in skin tissue are very similar to photoaging in human skin, both studies published in March 2021 used UVB, currently the most widely used model of photoaging.

This study found that NMN combined with Lactobacillus fermentum TKSN041 ameliorated UVB irradiation-induced skin damage in mice. Another study in October of the same year found that UVB-induced photodamage in mice was also blocked by intraperitoneal injection of NMN. The researchers concluded that these effects were likely achieved by activating the AMPK signalling pathway.

After UVB treatment, the thickness of the dermis of mice was significantly thinned, the thickness of the epidermis was increased, the number of collagen fibre bundles was reduced, and the subcutaneous tissues were disorganized and the boundary was not obvious. And the skin showed a chronic inflammatory reaction.

In contrast, after NMN treatment, UVB mice returned to normal thickness of the dermis and epidermis, maintained a normal collagen fibre structure and number, reduced mast cell production, and maintained an intact and organised skin structure. The researchers also found that NMN greatly increased serum antioxidant enzyme activity and improved skin inflammation in the mice. Furthermore, the study compared the effects of NMN with those of vitamin C, the "king of antioxidants," and showed that NMN's antioxidant effects were much higher than those of vitamin C. The researchers also found that NMN significantly increased the activity of serum antioxidant enzymes and improved skin inflammation in the mice.

On 12 June 2021, the laboratories of DHC Corporation in Japan published a study in the Journal of Photochemistry and Photobiology showing that UV damage activates the balancing act of NAD+ synthesising and NAD+ consuming enzymes, which determines the survival or dysfunction of human skin cells.

They showed that UV radiation activates nicotinamide-phosphate ribosyltransferase (NAMPT) to produce the NAD+ precursor NMN and activates the NAD+-depleting enzyme poly ADP ribose polymerase (PARP). If there is a problem with NAD+ synthesis during this equilibrium process, PARP will severely deplete NAD+ levels, leading to stagnant skin cell proliferation and dysfunction.

Interestingly, blocking NAD+ production by NAMPT allows PARP to excrete NAD+, but supplementation with the NAD+ precursor NMN (100 µM) or nicotinamide riboside (NR; 50 µM) restores the cell's ability to repair from UV damage. 

People who love beauty know that sun protection is very important, based on the cellular science point of view, the Japanese company DHC laboratory this study concluded that the skin sun triggers UV damage will activate the NAD + synthesis and NAD + depletion of the enzyme balance of behaviour, and ultimately will be a serious depletion of the level of NAD +, which will lead to the stagnation of the skin cell proliferation and dysfunction, leading to aging.

However, supplementation of NMN, the precursor molecule of NAD+, can restore the ability of cells to recover from UV damage and return the skin to its youthful and vigorous state. Therefore, supplementation of NMN can increase the ability of skin to recover from photo-aging and make the skin look younger and more beautiful.

The above research results confirm that NMN can protect skin cells from UV damage and prevent skin photoaging!