Kidney function undergoes a slow, progressive decline over a lifetime. The kidneys filter waste products from the blood and maintain the body’s balance of fluids and electrolytes. This natural aging process begins long before any symptoms appear. It is important to understand the difference between this normal decline and an accelerated, disease-driven loss of function.
The Biological Reality of Aging Kidneys
The gradual decrease in filtering capacity is directly tied to structural changes within the kidney tissue itself. The most significant change is the slow, continuous loss of nephrons, which are the millions of microscopic filtering units contained within each kidney. This process of nephron attrition begins around the age of 40 and can result in the loss of up to half of the original filtering units by the time a person reaches their seventies.
The physical loss of nephrons decreases the overall mass and size of the kidneys. The blood vessels supplying the kidneys can also stiffen with age, reducing renal blood flow. This blood flow can decrease by approximately 10% per decade after middle age. A diminished blood supply means the remaining filtering units receive less blood to clean, reducing the organ’s efficiency.
How Kidney Function is Measured
Doctors quantify the decline in kidney function primarily through a measure called the Glomerular Filtration Rate, or GFR. The GFR represents the volume of fluid the kidneys can filter from the blood each minute. Because directly measuring this rate is complex and impractical for routine checks, clinicians rely on an estimated GFR, or eGFR.
The eGFR is calculated using a formula that incorporates a patient’s age, sex, and the level of a substance called serum creatinine in the blood. Creatinine is a waste product generated by the normal wear and tear of muscle tissue. Healthy kidneys efficiently remove this creatinine from the bloodstream, meaning that a lower level generally indicates better muscle mass and kidney clearance.
If the kidneys are not filtering effectively, the level of creatinine in the blood rises. The eGFR calculation translates this creatinine level into an approximate filtration rate, with a result of 90 milliliters per minute per 1.73 square meters of body surface area or higher typically considered normal for a younger adult. This metric provides a simple, trackable number that allows healthcare providers to monitor kidney performance over time.
Distinguishing Normal Decline from Disease
It is important to differentiate between the expected, slow, age-related decline and the accelerated damage caused by Chronic Kidney Disease (CKD). CKD is a pathological state defined clinically by an eGFR that falls below 60 mL/min/1.73m² and persists for three months or more, often accompanied by other signs of kidney damage.
A significant issue arises because the age-related decline can push an elderly person’s eGFR into the range that technically meets the criteria for CKD, even in the absence of traditional disease markers. Experts note that an eGFR between 45 and 59 mL/min/1.73m² in a person over 70 may reflect normal aging rather than a true disease state, particularly if there are no signs of protein in the urine, known as albuminuria. Albuminuria is a much stronger indicator of genuine kidney damage, as healthy nephrons should retain blood proteins.
Kidney function decline is accelerated far beyond the normal aging rate by two pervasive chronic conditions: hypertension and diabetes. High blood pressure is a leading cause because it damages the delicate blood vessels within the kidneys, impairing their filtering ability. Similarly, consistently high blood sugar levels associated with diabetes scar the kidney’s filtering units over time. These conditions introduce pathological injury that accelerates decline toward kidney failure.
Strategies for Maintaining Kidney Health
While some decline is inevitable with age, several practical strategies can help preserve function and slow the rate of loss. Managing chronic conditions is paramount, particularly keeping blood pressure and blood sugar levels within target ranges set by a healthcare provider. Effective management of these conditions significantly reduces the stress placed on the filtering units.
Consistent hydration is also beneficial, as drinking enough water helps the kidneys flush out waste products efficiently. Older adults should be mindful of staying hydrated even if they do not feel particularly thirsty, since the body’s natural thirst response can diminish with age. Additionally, caution should be exercised with certain over-the-counter pain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen, because long-term or excessive use can be toxic to the kidneys.
Adopting a healthy lifestyle that includes regular physical activity and a balanced diet low in processed foods and excessive sodium also supports kidney function. For those with established kidney issues, a healthcare professional or renal dietitian can provide specific guidance on modifying protein, potassium, and phosphorus intake.