The Science of Aging

By Catherine Roy, January 20, 2023

older woman with gray hair holding a camera in nature

In recent years the field of longevity has exploded, with scientists making significant breakthroughs in understanding how we can live longer, healthier lives. 

As these scientists continue to uncover how and why we age, their research suggests that aging may actually be a somewhat modifiable process. Science-backed interventions show promise in slowing down the aging process and increasing lifespan. According to these experts, aging may not be inevitable.

What is aging and when does it start?

Aging is a gradual decrease in function due to the accumulation of cellular damage. [1] More broadly, aging is the culmination of the physiological changes that occur over our lifespans. While some of these changes are seemingly harmless (like graying hair and wrinkles) others have a more profound impact—affecting aspects of health like mobility, bone strength, and disease susceptibility. 

Aging is a complex, non-linear process that is considered to begin in the fourth decade of life, between the ages of 30-39 years. [2] However, each person ages at a unique rate. Some people maintain their mental capacity and stamina well into their later years, whereas others begin exhibiting signs of aging as early as their mid-20s. [3,4] While genetics and biology play a key role, the rate of aging is also significantly impacted by behavioral and psychological factors including diet, physical activity, smoking status, stress levels, sleep patterns, and social connections. [5-8]


Why do we age?

Initially, aging was believed to be an evolutionary benefit to the human species—aging and eventual death prevented overcrowding and allowed for the survival of beneficial genetic traits. [7] But, advances in research have made it clear that this complex, multifaceted process cannot be attributed to a singular cause. Rather the more widely accepted explanation is that aging is the result of multiple genetic, biological, and environmental processes combining, interacting, and overlapping with each other on a variety of levels.[7,9]


Theories on aging

Given the inherent complexities of aging, scientists have theorized for years about the exact mechanisms behind the process as they seek to understand the cause, effect, and what keeps it at bay. At one point, over 300 different theories attempted to explain the phenomenon. [7,9]

Advances in research geared towards unraveling the process have led to two prevailing categories of aging: programmed theories of aging and damage theories of aging


Programmed theory of aging

Programmed theories center around the notion that aging is an innate part of biology. Cells are programmed to decay and deliberately deteriorate in function over time. In other words, cells have a finite lifespan. [7,9,10]

  • Genetic theory: According to this theory, aging is caused by switching ‘on’ and ‘off’ certain genes. 
  • Endocrine theory: This theory links the pace of aging with hormone levels. Levels of hormones that control processes like blood sugar regulation decline with age and cause dysregulation in cellular processes.   
  • Immunological theory: This theory is based on the fact that the immune system is programmed to peak during adolescence and decline over time, resulting in increased susceptibility to illness and disease.  


Damage theory of aging

Damage theories of aging view aging not as inherent, but rather, as an accumulation of damage caused by environmental factors. According to this theory, wear and tear are the main drivers of aging. [7,9,10]

  • Wear and tear theory: This theory suggests that cells and tissues are not meant to live forever as they also have vital parts that wear out with continued use.
  • Rate of living theory: Based on this theory, the rate of an organism's metabolism determines lifespan, with a faster metabolism resulting in a shorter lifespan.  
  • Cross-linking theory: According to this theory, aging occurs as cross-linked proteins accumulate and damage cells and tissues.
  • Free-radical theory: This theory proposes that aging is caused by environmental free-radical exposure, which damages DNA, proteins, and lipids. Environmental exposures to cigarette smoke, pollution, and ultra-violet rays contribute to free radical production.
  • Genome instability theory: This theory states that aging results from damaged DNA, particularly mitochondrial DNA, that the body has been unable to repair. Over time, this damaged DNA accumulates and further hinders the DNA repair process. 
  • Information theory First proposed by Dr. David Sinclair in his book, Lifespan: Why We Age and Why We Don’t Have To, this theory attributes aging to a loss of information. As cells become damaged they lose the information encoding their identity. As damage accumulates, more cells lose their identity, and tissue and organ function begins to decline and result in aging.[11] Check out this article to read more on Dr. Sinclairs learnings since publishing Lifespan

Can you prevent aging? What to know about anti-aging habits

As research evolves, aging experts are reframing the aging process. Rather than just a set of innate biological processes that result in irreversible molecular and cellular changes, aging is a complex interaction between genetics and lifestyle. Though you can't fully prevent all aging processes from occurring, research shows that individuals have the power to extend their lifespan by altering key lifestyle aspects like diet, exercise, stress, and sleep. [12-14] 


Science-backed habits to live longer

While longevity may be the ultimate goal, these interventions not only focus on extending lifespan but extending healthspan—the number of years we live in good health—as well. 

  1. Eat broccoli sprouts: Broccoli sprouts are packed with sulforaphane, a powerful sulfur-containing compound. Sulforaphane activates pathways in the body that suppress inflammation, activate detoxification, and promote antioxidant action. [15] 
  2. Get quality sleep—but not too much: The body’s repair mechanisms occur while we sleep. One study examining the sleep habits of 1.3 million individuals found that those who slept between six to nine hours per night had the lowest risk of all-cause mortality compared to those who slept for less than six or more than nine hours per night. [16]
  3. Reduce red meat intake: Red and processed meat intake are associated with a greater risk of all-cause mortality and mortality from cardiovascular disease, the number one cause of death in the United States. [17,18] According to one study, swapping red meat for plant-based protein sources like beans or tofu is associated with a 13% lower risk of mortality in men and a 15% lower risk of mortality in women. 
  4. Consider intermittent fasting: Intermittent fasting contributes to longevity by eliciting the adaptive stress response within the body - a positive type of physiological stress. Adaptive stress activates different pathways in the body that help to increase the production of antioxidants, stimulate DNA repair, decrease inflammation, and clear out dead and damaged cells. [19]
  5. Keep stress levels in check: It is well established that high-stress levels negatively impact almost every aspect of health, including longevity. Research shows that those who can manage stress and experience positive emotions like happiness and joy live longer, healthier lives. [20]

Key takeaways

  • Aging is a decrease in functional capacity over time due to accumulated cellular damage. 
  • There is not one singular explanation as to why we age. Rather, aging is the result of complex interactions between our genetics and our environment.
  • There are two main categories of aging: programmed theories and damage theories
  • Based on the most recent scientific advances, researchers believe that the aging process can be slowed down. 
  • Eating a well-balanced diet, getting enough sleep, and managing stress levels are three key interventions that longevity experts agree on.



[1] Understanding the dynamics of the aging process. National Institute of Health. Accessed August 8, 2022.

[2] Dziechciaż M, Filip R. Biological psychological and social determinants of old age: bio-psycho-social aspects of human aging. Ann Agric Environ Med. 2014;21(4):835-838.

[3] Aging and Health. The World Health Organization. Accessed August 8, 2022. 

[4] Melzer D, Pilling LC, Ferrucci L. The genetics of human ageing. Nat Rev Genet. 2020;21(2):88-101.

[5] Crimmins EM. Social hallmarks of aging: Suggestions for geroscience research. Ageing Res Rev. 2020;63:101136.

[6] Passarino G, De Rango F, Montesanto A. Human longevity: Genetics or Lifestyle? It takes two to tango. Immun Ageing. 2016;13:12. Published 2016 Apr 5. 

[7] Kirkwood TB. Understanding the odd science of aging. Cell. 2005;120(4):437-447.

[8] DiLoreto R, Murphy CT. The cell biology of aging. Mol Biol Cell. 2015;26(25):4524-4531.

[9] da Costa JP, Vitorino R, Silva GM, Vogel C, Duarte AC, Rocha-Santos T. A synopsis on aging-Theories, mechanisms and future prospects. Ageing Res Rev. 2016;29:90-112.

[10] Jin K. Modern Biological Theories of Aging. Aging Dis. 2010;1(2):72-74.

[11]. Sinclair, David. Lifespan: why we age and why we don’t have to. Atria Books; 2019. 

[12] Muscat SM, Barrientos RM. Lifestyle modifications with anti-neuroinflammatory benefits in the aging population. Exp Gerontol. 2020;142:111144.

[13] Peskind ER, Li G, Shofer JB, et al. Influence of lifestyle modifications on age-related free radical injury to brain. JAMA Neurol. 2014;71(9):1150-1154.

[14] Mamalaki E, Charisis S, Anastasiou CA, et al. The Longitudinal Association of Lifestyle with Cognitive Health and Dementia Risk: Findings from the HELIAD Study. Nutrients. 2022;14(14):2818. Published 2022 Jul 8.

[15] Giacoppo S, Galuppo M, Montaut S, et al. An overview on neuroprotective effects of isothiocyanates for the treatment of neurodegenerative diseases. Fitoterapia. 2015;106:12-21.

[16] [17]Virtanen HEK, Voutilainen S, Koskinen TT, et al. Dietary proteins and protein sources and risk of death: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2019;109(5):1462-1471.

[18] Alshahrani SM, Fraser GE, Sabaté J, et al. Red and Processed Meat and Mortality in a Low Meat Intake Population. Nutrients. 2019;11(3):622. Published 2019 Mar 14.

[19] Saad R. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2020;382(18):1773.

[20] Okely JA, Weiss A, Gale CR. The interaction between stress and positive affect in predicting mortality. J Psychosom Res. 2017;100:53-60.

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