The Biology of Aging

As inevitable as aging is, what actually happens in our bodies as we age remains a mystery to most of us. In this guide, we’re going to explore what happens to our bodies as time passes. By getting a better understanding of the process, we’ll show how making even small habit changes can change your quality of life – no matter what age.

Understanding Physiologic Reserve

When we're born, we get two of many organs we need to live well, like kidneys and eyes. And there's a lot of extra ability within these organs. For example, you probably know that you can survive perfectly fine with a single kidney – it’s what makes kidney transplantation from a living donor possible. This might make you wonder: how can someone give away a vital organ and not have any health issues?

The answer lies in what's called physiologic reserve: the extra capacity that was given to us in each kidney (or other organ) at birth. Our organs have more ability to function than we actually need. Even if you go through life with both kidneys and never get kidney disease, you could lose up to 90% of your kidney function from when you were a child and still not have any symptoms of kidney failure. This extra capacity lets you donate a kidney without any harm to yourself.

It's not only about kidneys. When we're born, we have billions of brain cells that we'll never use. Our bodies have countless examples of having more capacity than needed.

The Impact of Age

The graph above illustrates the natural changes our bodies undergo with age, focusing on muscle strength and mass. It illustrates an important concept that many of us know: as we age, we gradually lose muscle.

This might initially seem disheartening. However, there's more to it – a silver lining – because we're born with more muscle capacity than we actually need. This built-in surplus means that for most people, significant issues from muscle loss won't surface until they are between 80 and 90 years old. We're often more likely to encounter other health challenges before muscle weakness becomes a major concern.

The graph also highlights the variability in our starting points, which is largely determined by genetics. This “genetic lottery” means that some individuals may begin their lives with the muscle strength of a marathon runner or the flexibility of a yogi, influencing when – or if – they’ll face mobility issues.

Moreover, the slow and almost imperceptible rate of muscle loss throughout life means that most of us, especially in our younger years, won't even notice this decline. Unless you're meticulously tracking your physical performance or undergoing regular scientific evaluations, the gradual decrease in muscle strength simply blends into the background of daily life.

While this graph highlights muscle strength, it serves as a stand-in for a broader phenomenon affecting nearly all bodily systems, emphasizing that this gradual reduction in our physiological reserves is a universal aspect of aging.  

Aging As Life Expectancy Has Increased

Life expectancy has increased rapidly over the past century. For most of history, life expectancy has been low – hovering in the mid-20s until the mid-1800s. This meant that most people died from causes unrelated to aging before they could deplete their physiological reserves.

The first significant increase in life expectancy happened during the 19th century. It was largely due to improvements in sanitation – the arrival of sewers and the availability of cleaner water reduced infectious diseases that took the lives of so many people.

In the past century, life expectancy has surged even further, reaching the late 70s and beyond thanks to advancements in modern medicine. Medical interventions now prevent or treat conditions that previously led to early death, such as many types of cancer, coronary artery disease, and even childbirth. This increase in life expectancy means that many people now live long enough to experience the effects of aging – including muscle weakness and other symptoms of physiological decline.

The concept of physiological reserve, or the "spare capacity" in our organs and systems, has become more relevant as more people live into old age. Whereas someone may not have ever come close to depleting their reserves in other parts of history, it is now being called upon daily in the lives of millions, and it impacts every system in our bodies: bone density, reaction time, and more.

Scientists have discovered that within the same individual, different rates of decline can be seen in different physiologic systems. For example, an 85 year old may have the kidney function (and reserve) of a 95 year old, but the reaction time of a 65 year old.

This becomes critically important as we near impairment because different organs and systems interact to enable to carry out activities; never does human activity (like walking or cooking) exclusively rely on one organ or physiologic system to accomplish the task.  Preparing a meal, for example, involves the muscular strength to stand, the manual dexterity to stir, and the visual and cognitive abilities to read an instruction label.

Using Evidence-Based Interventions to Help

The science of aging, known as gerontology, offers an encouraging insight: we can influence how quickly or slowly we age through various lifestyle choices and interventions. It doesn't matter if you're 50 or 90 when you start making these changes; even small adjustments can significantly impact your quality of life in later years.

These changes can delay the onset of disability, allowing you to live your later years more actively, rather than being confined to a bed or a nursing home. The key is to start making these changes, no matter how minor they may seem, as soon as you can.

For example, adopting sedentary habits at age 45, like becoming less active due to an injury or lifestyle change, can accelerate your progression towards disability. This might mean facing mobility issues or being confined to a wheelchair much earlier instead of enjoying mobility into your 80s or 90s. The graph below illustrates the impact.

But the good news is that the process works both ways. Just as negative lifestyle choices can hasten aging, positive ones can slow it down. Even simple actions, like walking regularly, can maintain muscle mass and delay the decline associated with aging. This is akin to making a small "course correction" early enough to avoid a major problem later on.

Furthermore, it's never too late to start making these adjustments. Studies have shown that older individuals, even those at risk of falling or who have already suffered falls and fractures, can benefit from interventions like resistance weight training. These activities can lead to improved muscle strength, decreased rates of falling and fracturing, and a delay in the onset of disability. This emphasizes the importance of making even positive changes to improve overall health, proving that it's possible to enjoy a higher quality of life for longer, regardless of when you start.

Getting Started

The idea here is pretty straightforward: small improvements in things like muscle strength can make a big difference, helping you avoid severe mobility issues without needing to achieve extraordinary fitness levels. The goal is to enhance daily functioning and quality of life, not to achieve a complete cure for all ailments.

This approach can feel at contrast with our traditional medical education, which often focuses on curing diseases at all costs. Many medical students enter their training aiming to cure diseases, influenced by a healthcare culture that emphasizes dramatic medical interventions and cures.

At times, this mindset can lead to either over-treatment or neglect of older patients, whose conditions are often chronic and not curable in the traditional sense. Instead, geriatric medicine focuses on managing these chronic conditions to improve the quality of life, even if a complete cure isn't possible. In other words, it’s important to not overlook the value of simpler interventions that can significantly improve a patient's life.

Improvements in care for older adults or those with chronic conditions don't necessarily come from high-tech solutions. Instead, they’re sometimes found in basic, "low tech, high touch" methods that address the practical aspects of daily life. For instance, reducing the need for pain medication or decreasing the frequency of urinary accidents can vastly improve a patient's quality of life, even though these improvements don't represent cures.

When it comes to aging, sometimes the use of advanced technology in medicine has overshadowed the importance of simple, effective care that enhances daily living. This approach to healthcare, focusing on practical improvements rather than cures, harks back to a time when doctors relied more on direct patient care and less on technology. It's a reminder that in the face of chronic conditions and aging, enhancing quality of life is as valuable, if not more so, than curing disease.