Bill was in his mid-30s when he came to my office complaining of fatigue, digestive issues, and skin problems. His doctor had told him that his thyroid numbers suggested low thyroid function.

One of the things Bill kept emphasizing was that he had been extremely healthy and vital throughout his twenties. Back then, he had plenty of energy. He worked long hours, slept little, exercised hard, and, by his own admission, partied hard as well. Then, around age 35—seemingly out of nowhere—things began to fall apart.

Other patients shared similar stories. They came in with frequent colds, low libido, poor stress tolerance, brain fog, or nagging health issues that never quite resolved. Like Bill, many of them were confused.

It didn’t make sense to them—but from a Chinese medicine perspective, this pattern makes a lot of sense, as the Kidney system plays a central role in all of these symptoms.

What the “Kidneys” Mean in Chinese Medicine

At first glance, this may sound surprising. The kidneys?

When Chinese medicine refers to an organ—such as the Kidneys—it is not referring only to the anatomical kidneys that filter blood and produce urine. In Chinese medicine, organs are best understood as code words for entire physiological systems (which include the actual anatomical organ as well).

The Kidney system governs growth and development, maturation and aging, reproduction and fertility, stress tolerance, brain function and memory, immune resilience, and recovery from illness and exertion.

We often refer to the substance that “runs” the Kidney system as Kidney Essence. This refers to our deep reserves of vitality, resilience, and biological strength—what you might think of as primal grit.

Some people are born with more of this reserve than others. Some people seem naturally robust, resilient, and energetic throughout life, while others struggle with health issues and fatigue from an early age. No one, however, has unlimited reserves.

What You’re Born With and What You Build

Chinese medicine distinguishes between two types of Kidney Essence, which helps explain why people with similar genetics can age and function very differently.

Prenatal Essence is the vitality we inherit from our parents at conception. It shapes our basic constitution and sets the framework for how resilient we are, how we handle stress, and how we age. Once prenatal essence is used, it cannot be fully replaced. This is why protecting it is considered central to longevity.

Fortunately, we are not limited to what we are born with.

Postnatal Essence is derived from how we live: what we eat, how well we sleep, how we breathe, and the physical and emotional demands placed on us. Postnatal essence supports and supplements the prenatal reserve, providing the Kidney system with the raw materials it needs to sustain vitality over time.

In other words, lifestyle choices can either protect our reserves—or accelerate their depletion.

Western Parallels

While Chinese medicine uses different language, there are clear parallels in Western physiology. Kidney essence is not a mystical concept, but a useful framework for talking about interconnected physiological processes.

The Kidney system overlaps with the endocrine system (particularly hormones involved in reproduction and stress response), systems that regulate growth and aging, neurotransmitter balance and cognitive resilience, and immune strength and recovery capacity.

From a Western perspective, people with a strong “Kidney system” show stable hormonal function, good stress tolerance, strong recovery from illness or exertion, healthy libido, and sustained mental clarity.

When this system becomes taxed—through chronic stress, sleep deprivation, under-nutrition, or overstimulation—the results are familiar: fatigue, burnout, low libido, brain fog, and reduced resilience.

How the Kidney System Gets Depleted

The Kidney system is gradually used over a lifetime. But it can be drained much faster when someone repeatedly expends energy without adequate recovery.

Common contributors include chronic high stress without rest, prolonged sleep deprivation, skipping meals or under-eating, excessive reliance on stimulants, and pushing through fatigue instead of restoring energy.

You’ve probably seen this: someone takes on a high-pressure job, sleeps poorly, relies on caffeine, and keeps going on willpower. A few years later, they look markedly older, feel depleted, and struggle to recover. In Chinese medicine, this is understood as burning through Kidney reserves.

Nourish Before You Expend

A central principle in Chinese medicine is simple but often overlooked: You must nourish energy before you spend it. You cannot run a depleted system on willpower alone.

This means eating regular, nourishing meals, sleeping enough to recover from stress, resting after intense periods of work or illness, and listening to early signs of fatigue instead of overriding them.

For women, this principle is especially important after childbirth, when the body has expended enormous resources. A gradual return to work and activity allows the system to rebuild rather than collapse later.

Certain lifestyle factors also draw on these reserves, which is why moderation and recovery matter—especially during periods of stress or low energy.

This is why Bill—who had a habit of “burning the candle at both ends” through overwork, stimulants, and weekend partying—began to experience so many health problems seemingly out of nowhere in his 30s. I see a similar pattern in many women who had several childbirths in their 20s and returned to work without allowing adequate time for recovery.

Protecting Your Kidneys

Whether someone is born with strong reserves or more modest ones, everyone benefits from protecting this system through eating enough and not skipping meals, prioritizing sleep, allowing recovery after stress or illness, avoiding chronic overstimulation, and tuning into fatigue rather than ignoring it.

People who maintain these habits tend to age more gradually, recover more fully, and maintain resilience longer.

The Bigger Picture

The Kidney system reminds us that health is not just about treating symptoms—it’s about preserving the foundations that allow the body to function well over time.

Think of your body like a car. If you take a new car on repeated cross-country trips without proper maintenance, it’s not surprising when problems show up later. Likewise, many midlife health issues aren’t sudden failures, but the result of years of unrecognized depletion.

The good news is that when people begin respecting their limits, nourishing themselves properly, and restoring balance, they often regain energy, clarity, and resilience they thought were gone for good.

As for Bill, after a year of treatment during which he learned to take better care of his body, he shared that he got married and soon after had a baby—something he knew would require energy and a better understanding of how to maintain his health.

Until next time, stay well—and take care of your reserves.