Cellular processes become less efficient as we advance in our 30’s, but we can boost a key pathway to prevent muscular aging.
During antiquity, age was considered a virtue and, conversely, a curse. The same is true of Geras, the ambivalent Greek god of old age, living on Mount Olympus but sometimes depicted as a simple malevolent spirit. Little is known about him. He is mentioned by a few Greek and Roman authors and represented as a shriveled old man on vases and other artifacts. His story is lost but his name remains – for example, in the term geriatric.
For us, Geras is nothing more than a representation of old age. He walks with a stick. His emaciated face, skinny limbs, and bent posture univocally evoke frailty. Being gradually deprived of physical strength is universally recognized as the main feature of old age.
The relation between aging and muscle weakness is known, but science has just begun to understand it. The good news is that researchers are now suggesting new ways to fight the frailty that comes with our advancing years. The bad news is that our decline begins earlier than one might think: our muscles seem to hit their prime and start weakening when we reach our 30s.
Age strikes before we can see it
Scientists have recently measured physical strength with advancing age in population samples in several clinical studies. Surprisingly, they observed a decline in muscle strength even in relatively young individuals. While the changes are modest from 30 to 50 years old, they are clearly measurable, with a rate of decline of 3-8% after the age of 30, and accelerating post 60 to 10-15% for every decade of life (1, 2).
We need to update our representation of aging. With his shrunken body, skinny legs and arms, the iconic Geras serves as an image of old-age frailty. But in reality, physical strength drops before we lose muscle mass in an obvious manner.
For scientists and clinicians, this observation has an important consequence: it means that aging impacts muscle quality before quantity. There has to be a mechanism at play inside our muscle cells that reduces their effectiveness as we age, and that consequently slowly undermines the optimal functioning of our muscles (3).
Mitochondria might be the key
The main suspects are the mitochondria. These are tiny powerhouses present inside all of our cells, providing them with the energy needed to carry out their daily biological functions. It has been shown that in muscle cells, as the mitochondria become less efficient at their jobs, the skeletal muscles on a whole become weaker, resulting in lower endurance and physical performance (4).
As we age, our mitochondria’s performance declines. But our cells can protect themselves thanks to a built-in mechanism called mitophagy, that enables cells to recycle their damaged mitochondria, leading to the biogenesis of new, healthy ones.
This recycling mechanism is gradually compromised with age. Instead of continually renewing their mitochondria, cells accumulate older, less efficient ones. While this might have many downsides, one of the most studied and better-known effects is the progressive loss of muscle power and strength (5).
By re-establishing proper recycling and renewing of mitochondria inside our cells, we can improve cellular function. Scientists believe that this approach holds promise to help manage the health of our muscles as we age. While it is not yet known if such a strategy would address the issues linked to muscle aging, there are good reasons to think that it could help (6).
Natural approaches are on the horizon that can improve mitochondrial health. Pre-clinical studies have shown that Urolithin A – a natural compound produced by gut microbiota from compounds called ellagitannins present in pomegranates, some berries, and nuts – stimulates mitophagy. In fact, Urolithin A promoted an elongated lifespan in primitive nematode worms and, more relevant, significantly increased (by about 40%), the physical endurance of aging rodents (7). Human clinical trials are currently underway to investigate how Urolithin A impacts muscle function and physical performance in humans.
Whatever our age, we are continually reminded of the physical limitations or our muscles, whether it’s during exercise or in simple daily activities like climbing stairs or even carrying heavy objects. Science is starting to uncover what is happening at a physiological and cellular level that is driving these limits that we all experience. With this new knowledge, it has become apparent that making efforts early in our lives, such as engaging in regular exercise, we can take control and limit the decline in muscle function as we get older. And importantly, new nutritional approaches are beginning to emerge that provide hope that a combination of lifestyle and nutritional intervention, no matter what your age is, can lead to healthier aging.
1)Moore, A. Z. et al. Difference in muscle quality over the adult life span and biological correlates in the Baltimore Longitudinal Study of Aging. J. Am. Geriatr. Soc., 62, 230–236 (2014).
2)Keller, K. et al., Strength and muscle mass loss with aging process. Age and strength loss. Muscles Ligaments Tendons J., 3, 346–350 (2013).
3)Goodpaster, B. H. et al. The loss of skeletal muscle strength, mass, and quality in older adults: the health, aging and body composition study. J. Gerontol. A Biol. Sci. Med. Sci., 61, 1059–1064 (2006).
4)Coen, P. M. et al., Skeletal muscle mitochondrial energetics are associated with maximal aerobic capacity and walking speed in older adults. J. Gerontol. A Biol. Sci. Med. Sci., 68, 447-55 (2013)
5)Sun, N., et al. The Mitochondrial Basis of Aging. Mol. Cell., 61, 654–666 (2016).
6)Gonzalez-Freire, M. et al. Searching for a mitochondrial root to the decline in muscle function with ageing. J. Cachexia Sarcopenia Muscle, 9, 435–440 (2018).
7)Ryu, D. et al. Urolithin A induces mitophagy and prolongs lifespan in C. elegans and increases muscle function in rodents. Nat. Med., 22, 879–888 (2016).