A Guide to the Stages of Aging

Biological hallmarks of aging

A 2023 research review suggested there may be 12 biological hallmarks of aging.

Genomic instability

Various external factors constantly affect your DNA. Some include:

• chemicals
• physical forces
• biological agents
• internal challenges such as:
  • mistakes during DNA copying
  • problems in chromosome separation
  • harmful oxygen-related processes
  • natural chemical reactions within cells

These types of damage can cause issues in your genetic material, including:

• tiny mutations
• missing pieces
• swapped sections between chromosomes
• shortened chromosome ends (telomeres)
• breaks in the DNA strands, rearranged chromosomes
• problems with the cells’ nuclear structures
• insertion of viruses or mobile genetic elements that disrupt genes

All these changes may play a role in typical aging and age-related diseases. To protect against such damage, organisms have developed complex systems to repair and maintain DNA in the cells’ nucleus and mitochondria. However, as you age, these repair systems become less effective, leading to increased damage and a higher presence of DNA in parts of the cells where it shouldn’t typically be present.

Telomere attrition

Damage to the protective tips of chromosomes, known as telomeres, plays a role in aging and related health problems. When the enzyme that helps maintain these telomeres (telomerase) is missing or not working properly, you can develop diseases like lung scarring, anemia, and other conditions that make it harder for tissues to heal and stay healthy.

Many animals, including humans and mice, naturally shorten their telomeres with age. Factors such as age, genetics, lifestyle choices, and social environment can affect the rate at which telomeres shorten. The shortening rate also depends on how actively the cells divide and can even help predict an organism’s life span across different species.

Epigenetic alterations

As you age, various changes occur that affect gene control and regulation, including:

• changes in the chemical tags on your DNA
• unusual changes to the proteins that help package DNA
• errors in how cells organize DNA
• problems with certain small molecules that help regulate genes

They affect how your body turns genes on or off and how cells work, which can lead to common health problems in older adulthood, such as:

• cancer
• brain diseases
• issues with metabolism
• bone problems

However, many of these changes are reversible.

​Loss of proteostasis

Aging and certain age-related health conditions link to a decline in your body’s ability to keep proteins balanced and working properly, such as:

• amyotrophic lateral sclerosis (ALS)
• Alzheimer’s disease
• Parkinson’s disease
• cataracts

This can cause atypical or damaged proteins to build up inside or outside the cells, sometimes clumping together to form small groups called plaques or deposits that can interfere with typical cell functions.

Deregulated nutrient sensing​

Your body’s system for detecting nutrients has remained quite similar throughout evolution. It involves substances outside your cells, like insulin and insulin-like growth factors (IGFs), which connect to specific receptors on cell surfaces. These receptors then trigger internal processes that send signals inside the cell.

A 2023 research review showed that reducing the activity of parts of this nutrient-detection system can help animals live longer and stay healthier. Additionally, studies involving humans found links between certain genes involved in this system — such as the FOXO3 gene — and a longer human life span.

Mitochondrial dysfunction

Mitochondria are tiny structures in cells that provide energy, but they can also trigger inflammation or cell death. This can occur when harmful molecules, like reactive oxygen species (ROS) or mitochondrial DNA, leak out of the mitochondria and activate other parts of the cells’ immune response or cell death processes.

As you age, mitochondria don’t work as well due to several reasons, such as:

• increased genetic damage
• problems with protein maintenance
• reduced ability to replace damaged mitochondria
• changes in their structure and movement

These issues weaken mitochondria’s energy-producing role, increase harmful molecules like ROS, and may cause mitochondrial membranes to become more permeable. This can lead to inflammation and cell death, which can lead to aging. Healthy mitochondria are essential for maintaining good health, and their decline over time plays a key role in the aging process.

Cellular senescence

Cellular senescence is a natural response in which cells stop dividing after experiencing damage, either suddenly or over time. In humans, these older cells build up in various body parts at different rates, ranging from 2 to 20 times more in people older than 65 years than in those under 35 years.

The types of cells most affected are often skin support cells (fibroblasts), cells lining blood vessels (endothelial cells), and immune cells, though any cell type can become senescent as you age. This process partially occurs from protective chromosome tips shortening called telomeres, which naturally happen as cells divide over the years. Even tissues that don’t usually divide much or at all, like your brain and heart, can still have some senescent cells present.

​Stem cell exhaustion

As you age, your body becomes less efficient at renewing and repairing tissues. Each organ has its own way of replacing old cells and healing damage. For example, in your muscles, special types of cells called satellite cells fix and renew muscle tissue. They follow a straightforward process, producing only one type of new cell to help repair muscle.

Your skin regularly sheds cells and often gets injured, so stem cells (the cells that can turn into different kinds of skin cells) live in many places. These cells are especially present around hair follicles. Each area makes its own new cells and expands its territory.

When you get injured, the ability of these cells to adapt and change (called plasticity) becomes important for healing, but this flexibility tends to decline with age.

Altered intercellular communication

As you age, the way your cells communicate with each other gradually changes. These changes make your body’s systems less efficient and less able to keep everything balanced and working properly.

This includes declines in the way your nerves, hormones, and other signaling processes work, such as:

• systems that use adrenaline
• dopamine
• insulin
• other hormones

It also involves a decrease in sex hormones, which happens as reproductive abilities diminish with age.

Chronic inflammation

As you age, your body tends to become more inflamed overall, a process sometimes called “inflammaging.” This increased inflammation can affect your whole body and links to various health issues such as:

• artery hardening
• brain inflammation
• joint problems like osteoarthritis
• disk degeneration in your spine

Additionally, your immune system’s T cells change as you age, leading to more aggressive types that boost inflammation. At the same time, your immune system becomes less effective at fighting off infections, detecting cancerous or aging cells, and preventing itself from attacking your body’s own cells. These changes make your body more prone to chronic inflammation and related health problems.

Compromised autophagy

Autophagy, which you can simply call “self-eating,” is a natural process where cells clean up and recycle damaged or unnecessary parts. It works by wrapping these materials in a double-layered bubble called an autophagosome, which then fuses with another cell structure called a lysosome that breaks down and removes the unnecessary or harmful cell parts.

This process manages proteins and helps remove other large molecules, such as damaged DNA, fats, sugars, and entire parts of the cells. It can also target invading germs and waste materials.

As you age, this cleanup process becomes less efficient, which contributes to cell and organ problems associated with aging.

Microbiome dysbiosis

In recent years, scientists have learned that the microbes living in your gut play an important role in many body functions, such as:

• helping digest and absorb food
• protecting you from harmful germs
• producing important substances like:
  • vitamins
  • certain amino acids
  • bile acids
  • short-chain fatty acids

These gut microbes also communicate with your brain and other body parts, helping keep you healthy overall. When this communication between your gut microbes and your body gets out of balance, it can lead to health problems such as:

• obesity
• type 2 diabetes
• inflammatory bowel disease (IBD)
• neurological conditions
• heart disease
• cancer

Because of these discoveries, there’s now a great deal of interest in studying how changes in gut microbes affect aging and age-related health issues.

Age-related stages and changes

There are various ways to define the stages of adult development. One of the comprehensive approaches used the following five broad stages.

It’s important to note that the cutoff age for each stage is discretionary since social roles typically relate to stages of development rather than directly to age.

Lifestyle factors that affect aging

Various factors can affect how you age:

• genetics
• physical activity
• eating habits
• alcohol consumption
• smoking status

While factors like genetics aren’t within your control, the other factors are within your ability to change and control.

Takeaways

Aging is a natural process that involves biological and physiological changes. There are various biological stages of aging that can affect your body and overall well-being.

Chronological stages of aging also affect how you live. However, the exact age ranges for these stages are discretionary.

Maintaining an active lifestyle and healthy eating habits can help you age in a healthy way and maintain your independence longer.