María Monterrubio

Do you regularly capitalize on the powers of putting the ellagitannins of pomegranate, walnuts, or raspberries into your body? Besides their inherent antioxidant ability, ellagitannins act within our gut as prebiotics and sources of antiaging postbiotics (which can also protect our skin from ultraviolet sunlight). Get yourself acquainted with the bodily effects of those powerhouses. If you care about your wellbeing, they’ll surely come in handy!

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Hi everyone! Even if you are not a skincare addict, you might have heard about pomegranate extracts, antioxidants, and omega fatty acids (highly present in walnuts). But you might not be that familiar with urolithin A when it comes to your health and youth. So bear with me!

What is urolithin A?

Urolithin A is a postbiotic. That is, a beneficial compound produced by some of the microorganisms that live in our body after they process certain types of molecules. To be more precise, specific bacteria yield urolithin A within our gut after we eat sources of ellagitannins, which are a class of polyphenols (aka antioxidant compounds).

Pomegranate is super rich in ellagitannins, followed by many berries (such as blackberries or raspberries), some nuts (like walnuts), and other fruits (with rosehip among them).

Urolithin A exits our gut through the bloodstream. And, from there, it gets to the different organs (including, of course, the skin), where it works its miracles.

How does urolithin A work?

Once urolithin A makes it to the peripheral organs (for instance, the skeletal muscle), it gets into the cells and stimulates the clearance of old mitochondria (the organelles that produce energy within our cells in the form of ATP) through a process called mitophagy.

At the same time, that allows the biogenesis of new mitochondria within the cells. As a result, old or damaged cells increase their energy levels and get back in shape (rejuvenate). 

That is especially relevant for organs that have high energy requirements. For instance, the brain, whose daily activity of coordinating all our functions is vast. The skeletal muscle needs plenty of energy to move. Or the skin, which has to renew and defend itself from external aggressors constantly.

The rejuvenating outcome of urolithin A on skeletal muscle fibers (which we need to move our bodies) resembles the impact that regular physical exercise has on them. A well-done clinical study (randomized, double-blind, placebo-controlled) including sedentary, older, healthy people (aged 61 to 85 years) confirmed the effects seen at the cellular level.

Those who took oral urolithin A daily (1000 mg a day for 28 days) showed no adverse effects (or accumulation of urolithin A over time), increased biomarkers of mitochondrial health, and more healthy mitochondria in skeletal tissue biopsies. They also presented better systemic mitochondrial efficacy.

Therefore, the positive impact of taking urolithin A daily on mitochondria goes beyond the skeletal muscle and affects the organism as a whole. An overall boost of mitochondrial function increases our general energy levels that, if sustained, translate into a younger biological age.

Indeed, enhanced energy levels (and higher levels of the molecules that allow that, such as ATP and NAD+/NADH) are scientifically one of the hallmarks of slow aging.

For the moment, there are no known edible natural sources of urolithin A. However, given its proven health benefits, the FDA (the Food and Drug Administration, which regulates nutritional supplements and medicines in the USA) approved the use of urolithin A as a food supplement (in quantities from 250 mg to 1000 mg a day). So, if you don’t ingest pomegranate every day, there’s the choice of taking an urolithin A supplement.

Does everybody produce urolithin A after the ingestion of sources of ellagitannins?

The answer is no. The composition of the gut microbiota is individual and pretty much the same throughout our lifetime. Some people seem to lack the bacteria that yield urolithin A (UA) and therefore do not excrete urolithin A glucuronide after eating pomegranate, which is the form of UA that runs in the systemic circulation after leaving the gut.

That said, since nobody knows whether they can produce urolithin A in the first instance, the food supplements may come in handy.

What can urolithin A derived from pomegranate do for your skin?

Direct topical application of pomegranate extract can reduce the skin damage from exposure to UVB radiation, presumably due to the free radical scavenging and other actions of ellagitannins (whose in vitro antioxidant and anti-inflammatory properties are well-known).

As happens in the gut, some microorganisms of the skin microbiota might convert ellagitannins (such as ellagic acid) into urolithin A (or other compounds) that could, in turn, provide protection against UV radiation (we do not know this yet).

However, after oral ingestion of pomegranate extract or juice, urolithin A appears to be involved firsthand in the protection against UVB light.

The Minimal Erythema Dose (MED) is the lowest UVB dose and time of exposure required to induce skin erythema (the redness that we see when our skin is about to burn).

Thus, oral or topical compounds with photo-protective properties against UVB light increase the MED. That means that if you ingest (or apply) those compounds, your skin can resist a more intense UVB light exposure before getting burned.

There is a recent study (of 2019) where 74 women (with phototypes II-IV, or medium skin tones) took either pomegranate extract (1000 mg/day) or juice (237 ml/day), or a placebo (nothing) for 12 weeks. After those three months, the ingestion of pomegranate extract and pomegranate juice significantly augmented the MED (compared to placebo).

In the pomegranate extract group, those women who hadn’t the ability to produce urolithin A presented a lower MED (lower photo-protection) at the end of the study than those who had. That shows that urolithin A is at least partly responsible for the photo-protective effect.

It also appears that the juice may offer somehow higher photo-protection than the extract since the people who did not produce urolithin A in the juice group displayed a similarly increased MED as the UA producers.

How does urolithin A function within the skin? 

As seen in other organs, urolithin A could increase the removal of damaged mitochondria and the biogenesis of new mitochondria. The replacement of old mitochondria with fresh mitochondria entails an improvement not only in cellular energy. It also heightens the ability of the cells to counteract the oxidative damage otherwise caused by UVB light. 

Like that, by stimulating mitochondrial turnover, urolithin A may increase the MED and boost photo-protection, given that:

– some of the intrinsic cellular antioxidant systems are in the mitochondria – so the more fully functional mitochondria, the merrier;  

– the cell needs constant fresh energy (that the mitochondria provide) to regenerate its inherent antioxidant systems and keep them up and running.

Additionally, the urolithin A molecules might be acting directly as free radical scavengers themselves or by activating molecules (such as the Nrf2 factor) that stimulate the expression of proteins involved in other detoxification mechanisms of the cell.

Those actions would help lessen the damage to the DNA upon UVB exposure and, hence, delay the cutaneous erythema response.

Likewise, urolithin A could also help counteract the effects of air pollutants on the skin through similar mechanisms (see the image below).

Would urolithin A have similar effects when applied to the skin?

Nobody has evaluated yet whether urolithin A could be a cutaneous photo-protectant or skin youth booster (through the optimization of mitochondrial recycling) after topical application.

However, we know that ellagic acid, which has a higher molecular weight (302.197 Daltons) than urolithin A, penetrates the skin and can display anti-inflammatory and depigmenting effects.

So Urolithin A, due to its smaller size (228.203 Da) and similar chemical nature, most likely will penetrate the skin. Then why not? It seems plausible that urolithin A could work topically based on all the pre-existing data (that I have partly discussed above).

In this regard, I have found a patent that claims the topical use of Urolithin A (from 0.2% to 1%) for the localized treatment of inflammatory skin conditions (since it seems to diminish the number of immune cells that infiltrate the skin and foster cutaneous inflammation).

Who knows? Maybe sooner than not, we will be able to trust the application of urolithin A to foster our UV defense, decrease inflammation, and boost the youth of the skin (and a lower cutaneous biological age).

For now, we will have to rely on our daily dose of pomegranate, berries, and nuts (or our daily urolithin A food supplement).

I hope you enjoyed this post.

If so, please hit like! And leave any questions you may have in the comments below. I will be happy to answer them.

Also, do not forget to follow me on Instagram for extra perks (@drmariamonterrubio) 😉

Thank you, and see you soon!

María

Main references

Impact of the natural compound Urolithin A on Health, Disease, and Aging. D’Amico A et al., Trends Mol Med, 2021; 27 (7): 687-699.

Pomegranate juice and extract consumption increases the resistance to UVB-induced erythema and changes the skin microbiome in healthy women: a randomized controlled trial. Henning SM et al., Sci Rep, 2019; 9 (1): 14528.

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