Ageing ranks alongside sleep as one of the fundamental mysteries of human biology. What drives the body to slow down, its cells to cease dividing, and its organs to succumb to increasing illness and disability? While definitive answers remain elusive, theories generally fall into two categories: gradual damage over time and genetic programming.
The first set of theories suggests that ageing occurs due to accumulated wear and tear on the body’s tissues over the years. Factors such as the buildup of waste products within cells, the failure of backup systems, and the gradual breakdown of repair mechanisms contribute to the body wearing out, akin to an ageing car.
On the other hand, the second group posits that ageing is governed by our genes, regulated by an internal molecular clock set to a specific timetable for each species. Evidence supporting this theory comes from animal studies where alterations to a single gene have been shown to extend lifespan. From an evolutionary perspective, natural selection’s influence diminishes significantly after the reproductive age, favouring genes that enhance fitness and reproduction early in life, often at the expense of long-term maintenance.
At the cellular level, ageing initiates within the body’s smallest units: cells. The mechanisms behind how and why cells age remain topics of debate, but some insights have emerged. Biologist Leonard Hayflick’s discovery in the 1960s revealed that cultured cells undergo a finite number of divisions, known as the Hayflick limit. Although exceptions exist for stem cells and cancer cells, this limit applies to most human tissues, with cells from older individuals dividing fewer times.
Telomeres stretches of DNA that cap chromosome ends, play a crucial role in cell ageing. Each cell division results in the gradual shortening of telomeres until they reach a critical length, halting cell division entirely. Telomerase, an enzyme found in immortal cells like stem cells, can repair telomeres after division, but its activity is limited in non-dividing cells and may promote cancer in dividing cells.
Environmental factors also influence telomere length, with individuals experiencing stressful lives often exhibiting shorter telomeres. Conversely, adopting healthier lifestyles, including moderate exercise and stress-reducing practices, has been associated with telomere lengthening.
Ageing affects nearly all body systems, with changes to bones and muscles significantly impacting daily life. Bone density decreases, and muscle mass declines while fat accumulates between the ages of 30 and 75. The heart, blood vessels, and lungs, although durable structures undergo changes with age, compounded by lifestyle factors like smoking and obesity.
Concerns about ageing often centre on cognitive decline and sensory changes. While the brain’s tissues shrink slightly, it maintains functionality through neuron connections and neuroplasticity. The senses, particularly vision and hearing, may deteriorate with age due to presbyopia and long-term exposure to loud noises, respectively.
In summary, while ageing remains a complex phenomenon with many unanswered questions, insights into its mechanisms offer potential avenues for promoting healthy ageing and mitigating age-related decline.
