Comprehensive Guide to Optimizing Kidney Function: Enhancing Detoxification Systems

The kidneys are among the most critical organs in the human body. They play a vital role in maintaining homeostasis by filtering waste products from the blood and regulating essential bodily functions. Kidneys serve as filters that remove toxins, excess salts, glucose, urea, ammonia, and other metabolic waste products to maintain the body's water balance and electrolyte levels.

Additionally, they contribute to hormone regulation, muscle contraction, and electrical activity in the heart, ensuring proper bodily functions such as blood pressure maintenance and energy production.

This article explores ways to support kidney health, improve detoxification, and prevent potential issues. Following these steps can help protect kidneys and maintain strong overall health.

The main physiological functions of the kidneys

1. Waste Filtering

The kidneys remove toxic substances such as urea, ammonia, excess salts, glucose, and fatty acids from the body through urine formation (excretion). This system ensures that harmful waste does not accumulate within blood vessels, preventing potential damage to tissues and organs.(1)

Glomerular filtration is the first step in forming urine, driven by hydrostatic pressure across a three-layer filtration barrier that prevents blood cells and large proteins from crossing. The resulting net filtration pressure depends on the balance between fluid pressure in the glomerular capillaries, opposing capsular hydrostatic pressure, and colloid osmotic pressure. Glomerular filtration rate (GFR), which usually ranges from 120 to 125 mL/min, reflects net filtration pressure, membrane permeability, and total surface area.(2)

2. Regulation of Water Balance

The kidneys play a critical role in maintaining proper hydration levels by regulating the balance between water intake and output. They also filter out excess salts and minerals (like calcium), ensuring that body fluids remain isotonic and electrolyte levels are balanced.

Humans have a sensitive physiological thirst mechanism to balance body water but often drink it for non-regulatory reasons such as taste or social context. Though the kidneys can manage short-term water surpluses or deficits, the availability of sweetened or alcoholic drinks in wealthier societies frequently leads to confusion about actual thirst needs.(3)

3. Support for Metabolic Processes

Kidneys support metabolic functions such as energy production, hormone regulation, and muscle contraction:

Hormone Regulation: The kidneys regulate hormones like insulin (GI) and growth hormone, essential for metabolism.(4-5)
Energy Production: During exercise, muscles generate lactic acid, which the kidneys convert into acetic acid to prevent the accumulation of toxic waste products.(6)

4. Urine Formation

The process of urine formation involves complex interactions:(7)

The urogenital system (kidneys) filters blood and produces urine.
The circulatory system supports this process by delivering necessary nutrients.
The autonomic nervous system controls urinary flow, ensuring efficient management of bodily needs.

5. Dehydration Management

Proper hydration is crucial for kidney function.(8) Dehydration can lead to:

Reduced urine output (dysuria)
Depletion of essential minerals and electrolytes in the body
Impaired filtration efficiency

BODY FLUID BALANCE

Approximately 65 % of the human body consists of water. Dehydration by just a few percentage points significantly impairs general performance. Regulation of the body's fluid balance is one of the primary regulation mechanisms.

A human being can survive without food for extended periods, but as little as 3–5 days without fluids is likely to lead to death. Similarly, sufficient fluid intake during and after exercise is paramount. The body can only absorb a relatively small amount of fluid under exertion. This volume varies from 300 to 1,200 milliliters per hour.(9)

According to official guidelines, one should drink at least 1–1.5 liters of water per day, preferably 2–3 liters, depending on daily activity level and air temperature.(10) The daily fluid intake should be increased by at least a liter per hour of exercise. The elderly should also drink more fluids due to the impaired ability of their kidneys to filter urine.(11) A simple indicator of sufficient hydration is the color and volume of urine.

Light-yellow urine and a sizeable urinary volume indicate that the body's fluid balance is correct. Conversely, dark-colored urine and a small urinary volume are indicative of dehydration.(12) On the other hand, entirely colorless urine indicates that the fluid intake is too large in volume or too rapid.

The Role of Diet in Optimizing Kidney Function

Antioxidants in Supporting Kidney Function

Antioxidants neutralize free radicals generated during cellular respiration, protecting the kidneys from oxidative stress caused by environmental factors such as smoke, pollution, and harmful habits like excessive alcohol consumption.(13)

These include:

Berries: Rich in vitamin C and antioxidants (polyphenols, in particular), they protect against chronic diseases while supporting kidney function.
Nuts and Seeds: Contain flavonoids that shield against premature aging and support immune system health, indirectly benefiting kidney function.
Leafy Greens: Such as spinach and kale, are excellent sources of vitamins, minerals, and antioxidants (including vitamins A, C, and E) that help neutralize free radicals in the body. However, eating too much raw kale and spinach may increase the body's oxalate accumulation, which may predispose to kidney stones.(14)
Dark Chocolate: Contains compounds like epicatechin, which combat free radicals while maintaining nutrient balance. Interestingly, dark chocolate use can increase renal medullary oxygenation, leading to better kidney function.(15) However, using too much dark chocolate may increase oxalate burden and the risk of kidney stones.

Protein-Optimized Diets for Optimal Kidney Function

Proteins are vital for muscle repair, nerve signaling, and hormone regulation, all supporting kidney health. In healthy individuals, a high-protein diet is not harmful to the kidneys. However, restricting protein intake reduces the kidney's stress and alleviates the deficiency in individuals already suffering from kidney deficiency.(16-17) In fact, protein has been found to lower blood pressure and thus ease the stress placed on the kidneys.(18)

When improving kidney function through nutrition, the focus is on an anti-inflammatory and nutrient-rich diet.(19) Keeping the intestines in good condition is also important for kidney function. In particular, the leaky gut syndrome may cause toxins to be released into the circulation, potentially causing kidney damage.(20) Studies have found that a pro-inflammatory diet, such as SAD (Standard American Diet), significantly impairs kidney function.(21)

In the event of impaired kidney function, it is recommended to (at least temporarily) limit sodium, potassium and phosphorus intake from food.

The Role of Fiber in Supporting Kidney Health

Fiber contributes to regular bowel function by adding bulk to stool and improving transit time. This reduces constipation and supports the efficient elimination of waste products. Adequate fiber intake also promotes beneficial gut bacteria, known collectively as the gut microbiome, which helps break down nutrients and influences how toxins are processed before they enter the bloodstream.

A well-balanced gut microbiome can lower the production of compounds like p-cresyl sulfate and indoxyl sulfate, which place extra demands on the kidneys. When fewer toxins circulate, the kidneys can focus on filtering usual metabolic byproducts. Short-chain fatty acids from fiber fermentation also help maintain the gut lining, reduce inflammation, and regulate various metabolic pathways that affect kidney health.(22)

Emerging research indicates that the gut and kidneys engage in two-way communication, sometimes called the "gut-kidney axis." A high-fiber diet fosters a positive microbial environment, reducing toxic load and protecting kidney function. By improving nutrient absorption and intestinal barrier integrity, fiber creates a healthier internal environment that indirectly benefits the kidneys.(23)

Foods and supplements that support kidney function include:

Flavonoid-rich foods, in general, support kidney function(24)
Blueberries (rich in anthocyanins)(25)
Cranberries (improve the condition of urinary tracts and ureters and inhibit infections)(26)
Alkaline foods such as vegetables, berries, and fruits (a high dietary acid load impairs kidney function)(27)
Resveratrol (animal tests have found it to reduce inflammation and oxidative stress in the kidneys)(28)
Dandelion(29)
Curcumin(30)
Nettle (lowers blood pressure and acts as a diuretic)(31)
Silybum marianum (Milk thistle)(32)
Reishi (animal tests have found it to inhibit kidney damage)(33-34)
Schisandra (five-flavor berry) (findings from animal tests)(35)
Lemon juice (inhibits the formation of kidney stones)(36)
Vitamin C (human and animal tests have found it to protect kidneys in connection with kidney disease)(37-39)
Excessive vitamin C use may be a predisposing factor for kidney stones (at least in men)(40)
Antioxidants, in general, may be helpful in the early stages of impaired kidney function(41)
Kidney deficiency causes impaired nitric oxide (NO) production; therefore, NO production-boosting foods (and amino acids) may help improve kidney function(42)
- Beetroot
- Arginine
- Citrulline malate

Lifestyle factors improving kidney function include:(43-45)

Avoiding (or quitting) smoking
Moderate exercise that strengthens the circulatory system
Sufficient fluid intake
Good control of blood sugar and avoiding diabetes
Maintaining normal body weight
Maintaining a normal blood pressure level

Monitoring and Testing For Kidney Function

When taking annual lab tests, it is also essential to do comprehensive kidney function tests. These include the following:

Electrolyte levels (Sodium and Potassium): Ensures proper hydration and salt balance.
Blood urea nitrogen (BUN): Measures kidney filtration efficiency.
Creatinine: Indicates kidney disease severity or recovery.
Cystatin-C: A more delicate marker of kidney damage than creatinine.

Sodium

Sodium is the sixth most common element in the earth's crust and one of the primary macrominerals. Its chemical symbol is Na. Sodium occurs in all animals and in many plants as salt or sodium chloride (NaCl). An adult human weighing 70 kg contains approximately 100 g of sodium, 40 % located in the bones and 60 % in the cellular and intercellular fluids.

Sodium (and chloride) function in extracellular fluid by regulating blood pressure and extracellular fluid volume. This includes blood plasma, interstitial (intercellular) fluid, and transcellular fluid (cerebrospinal fluid, synovial fluid, etc.) Regulating this balance is crucial for the cell membrane potential and the sodium-potassium-ATPase pump (see section "Potassium" for more information). The function and number of these pumps vary by physical activity, fasting, age, various hormones, and medication.

Sodium is the major cation in extracellular fluid (cf. potassium being the major cation in intracellular fluid). Its presence outside cells is 10 times higher than inside cells.(46)

HYPONATREMIA

Hyponatremia, or low sodium levels in the blood, may develop for various reasons. Generally, the body strives to maintain a steady sodium level in the blood. Hyponatremia is very rarely caused by insufficient sodium in food. Excess sodium in food does not lead to excessive sodium in the blood, as the kidneys filter the excess sodium.

In practice, hyponatremia can develop in two ways: due to severe sodium loss or excessive water in the body (dilutional hyponatremia). In the latter, all body fluids are diluted, causing a decrease in sodium levels. Usually, hyponatremia is caused by excessive water in the body. Hyponatremia caused by sodium loss may occur after several days of severe diarrhea and vomiting. This usually requires hospital care and intravenous hydration. Hyponatremia is more common in the elderly, particularly in individuals with long-term illnesses such as cardiovascular disease, cancer, or diabetes.(47)

Hyponatremia symptoms include:

Headache
Nausea and vomiting
Muscle cramps
Fatigue
Disorientation
Fainting

Many drugs form a predisposing factor for hyponatremia, particularly when taken in large doses over a long period. These include diuretics, ACE inhibitors, anti-inflammatory drugs, opiate-based analgesics, SSRIs, tricyclic antidepressants, carbamazepine, and lamotrigine. Another predisposing factor for hyponatremia is excessive endurance training, which often involves excessive drinking.(48)

HYPERNATREMIA

Hypernatremia, or high sodium levels in the blood, may develop for various reasons. The blood sodium level increases when the individual is dehydrated, i.e., has insufficient water intake or loses excessive amounts of water through the kidneys. This does not occur in a healthy individual, as the thirst center in the brain activates and dehydration is prevented by drinking water. If the thirst center does not function properly and there is insufficient water intake, the resulting consequences may include dehydration and hypernatremia. This may occur, for example, in elderly individuals with anomalies in brain function.(49) Sometimes, hypernatremia may also occur in connection with severe diarrhea and vomiting, causing excessive water loss.

A significant majority of sodium intake comes from the salt contained in food. However, excessive sodium intake from food does not cause hypernatremia in healthy individuals. This is because sodium-rich food causes thirst, which in turn increases water intake. At the same time, the kidneys filter excessive sodium. Severe hypernatremia involves blood sodium levels over 155 nmol/L (the normal range being 137–145 nmol/L).

SODIUM (SALT) INTAKE FROM FOOD

The official minimum intake guideline for sodium in Finland is approximately 1.5 grams per day. The population-level guideline for the maximum salt intake for adults is up to 5 g/day, the equivalent of 2 g/day in sodium.

The average salt (NaCl) intake for adult Finnish men (aged 25–64) is 8.9 g per day (3.5 g of sodium) and for adult women (aged 25–64) it is 6.5 g per day (2.6 g of sodium). Based on the FinRavinto 2012 study, the recommendation for men is less than 7 g/day (Na 2.4 g) and for women less than 6 g/day (Na 2.8 g) (cf. Current guideline of 5 g/day). The results suggest that Finns consume sufficient (often excessive) salt (NaCl) compared to the guidelines.

It is worth noting that although excessive salt intake (more than 6 g/day) is linked to high blood pressure, low salt intake (less than 3 g/day) is an even greater health risk.(50) Another important factor is that Finns consume too much poor-quality, refined table salt lacking in other minerals. Some individuals are more sensitive to salt than others. According to estimates, approximately 26% of individuals with normal and 51% with high blood pressure are sensitive to salt.(51)

The recommended dietary allowance (RDA) for salt in the United States has been up to 5.8 g/day (equivalent to 2.3 g of sodium). According to studies, guidelines that are lower than these are not helpful and may even be harmful to people with diabetes, kidney disease, or cardiovascular disease.(52)

In 2019, the Food and Nutrition Board (FNB) of the National Academy of Medicine revised sodium's Dietary Reference Intakes (DRIs). The FNB did not find sufficient evidence to determine an Estimated Average Requirement (EAR) and derive a Recommended Dietary Allowance (RDA). Instead, they established an adequate intake (AI) for sodium.(53)

Summary:

Generally, people consume too much poor-quality salt (hidden salt, added refined salt) and insufficient mineral-rich salt. One can consume too much or not enough salt. Excessive salt intake and insufficient potassium intake can harm health.

Upgrade salt to a high-quality one (see the end of the chapter). Consume plenty of vegetables, berries, and fruits to secure optimal potassium intake.

MEASURING SODIUM LEVELS IN THE LABORATORY:

The body-sodium balance is primarily measured from the blood (plasma or serum). Sodium secretion can be assessed by measuring sodium levels in the urine. The sodium in the urine depends on sodium (salt) intake from food. Higher amounts are secreted when the food is high in sodium or the event of damage to the renal corpuscle, adrenal gland deficiency, or due to diuretics. If there is little sodium in the urine despite normal sodium intake from food, the finding may suggest low sodium levels in the body.(54)

Typical reference range (S-Na):

Adults: 137–145 nmol/L

FOODS WITH THE HIGHEST SODIUM CONTENT (source: the Fineli database)

The figures below refer to sodium levels. The salt (NaCl) amount can be calculated by multiplying this by 2.548.

Himalayan rock salt (38,069 mg / 100 g)
Sea salt (37,600 mg / 100 g)
Baking soda (27,360 mg / 100 g)
Mineral salt (21,000 mg / 100 g)
Baking powder (11,800 mg / 100 g)
Pickled herring, preserved in barrel (4,960.9 mg / 100 g)
Anchovies (4,140 mg / 100 g)
Roe, with salt (2,039.5 mg / 100 g)
Olives, on average (1,920 mg / 100 g)
Bacon, fried (1,342.5 mg / 100 g)
Warm-smoked whitefish (1,090 mg / 100 g)
Caviar, sturgeon roe (991.4 mg / 100 g)

Foods rich in poor-quality hidden salt include soy sauce, metworst (salami), many meal replacement products, tinned foods, bread, crackers, biscuits, chips and crisps, mustard, ketchup, processed cheese, deli meat, sausages, and countless convenience foods.

RECOMMENDED HIGH-QUALITY SALT PRODUCTS FOR COOKING:

Kalahari salt & Oryx desert salt
Himalayan rock salt/pink salt/crystal salt
Black salt
Celtic sea salt
Guerande sea salt
Sea salt
- For example, Maldon pure sea salt crystal flakes
Pansalt
- It contains less sodium and more potassium
- Suitable for those with potassium deficiency who also have a problem with excessive sodium

Potassium

Potassium is one of the primary macrominerals in the body. It is a cation (a positively charged ion). The chemical symbol of potassium is K. Potassium is one of the primary minerals in nature. It is essential to both animals and plants.

The human body contains more than 100 grams of potassium. It is an essential electrolyte in the cells and their primary positive cation. This means that potassium maintains, for example, the action potential of neurons used to pass on nerve impulses. Conversely, the major cation outside the cells is sodium (Na+). Potassium is also required for normal protein synthesis in the muscles.

The sodium regulates the transfer of potassium and sodium through the cell membranes-potassium-ATPase pump, which uses an ATP molecule to move three Na+ ions out of the cells and two K+ ions into the cells. This maintains the action potential of the cell membranes. It is estimated that the function of these cell membrane pumps makes up 20–40 % of the resting energy expenditure of an adult human. These pumps regulate, for example, the passage of nerve impulses, muscle contractions, and electrical heart functions. In addition to the abovementioned functions, potassium is required as a cofactor in carbohydrate metabolism pyruvate kinase.(55)

The kidneys are an important part of potassium metabolism and are linked to sodium metabolism. The kidney glomeruli filter approximately 180 liters of blood plasma daily, containing 600 g sodium and 33 g potassium. If the kidneys' filtration process does not function precisely or if the potassium intake from food is insufficient, a potentially dangerous condition called hypokalemia may develop. If left untreated, it can lead to death.

Predisposing conditions for hypokalemia include:(56)

Severe vomiting and diarrhea (potassium loss)
Excessive laxative use
Severe magnesium deficiency
Heart failure
Alcoholism
Continuous use of thiazide diuretics or furosemide
Anorexia or bulimia
Long-term consumption of large amounts of licorice

Hypokalemia symptoms include:

Fatigue and exhaustion
Muscular weakness and cramps
Intestinal paralysis
Heart palpitations
Muscular paralysis (in extreme cases)

According to epidemiological studies, increased potassium intake from food is linked to a lowered stroke risk. This is particularly true of individuals whose potassium intake from food was previously relatively low and who increased the amount of fruits and vegetables in their diet. Sufficient potassium (and magnesium) intake has also been linked to improved bone density, particularly in women and elderly men.(57) Foods containing potassium are generally also rich in bicarbonate, which acts as a pH buffer in the body. Sufficient bicarbonate intake helps balance bone metabolism.(58)

Potassium intake has also been found to affect blood pressure positively; high potassium intake from food is linked to lower blood pressure than significantly lower potassium intake.(59) A daily potassium intake of approximately 4,100 mg was linked to, on average, 2.8/1.1 mmHg (systolic/diastolic) lower blood pressure levels in healthy individuals and up to 7.2/2.8 mmHg (systolic/ diastolic) lower blood pressure levels in individuals with hypertension whose potassium intake from food was only 1,700 mg/day.(60) Potassium supplements may also significantly lower blood pressure levels (-3.11/1.97 mmHg), but a medical expert should approve and monitor any such use.(61)

The use of potassium supplements can have side effects in some cases. These include:

Nausea and vomiting
Intestinal discomfort
Diarrhea

HYPERKALEMIA (ELEVATED POTASSIUM LEVELS IN BLOOD)

Hyperkalemia means excessive potassium intake. This is not likely in terms of potassium from food, but when potassium is taken as a supplement, hyperkalemia is possible, although unlikely. However, a Finnish Duodecim review (2018) states: "The potassium levels in the blood of a healthy individual cannot become excessive even if potassium-rich food or potassium tablets are digested. The excess potassium is excreted into the urine by the kidneys."

On the other hand, it has been found that single doses of potassium supplements over 18 g can cause severe hyperkalemia. In Finland, the maximum recommended potassium supplement dose is 3.5 grams. In the US, the maximum recommended dose is 3,400 mg.

Many types of medication can cause hyperkalemia (including hypertension drugs containing potassium, ACE inhibitors, anti-inflammatory drugs, and some antibiotics such as Trimetoprim-Sulfa, heparin, digitalis, beta and alpha-blockers, and angiotensin receptor blockers).

POTASSIUM INTAKE FROM FOOD

The recommended intake of potassium for adults is typically:

Men: 3,500 mg per day
Women: 3,100 mg per day
Pregnant women: 3,100 mg per day
Breastfeeding women: 3,100 mg per day

The average potassium intake for adult Finnish men (aged 25–64) is 4,100 mg per day; for adult women (aged 25–64), it is 3,400 mg per day. The results indicate that Finnish people get enough potassium from food compared to the guidelines. Whether the guidelines for potassium intake are sufficient for optimal health and well-being is a question worth considering. According to clinical studies, the ideal potassium intake to prevent, for example, stroke, hypertension, osteoporosis or kidney stones is 4,700 mg/day.(62)

The recommended dietary allowance (RDA) for potassium in the United States is 4,700 mg/day for men and women and 5,100 mg/day for pregnant women. On the other hand, in the United States, potassium intake is very low compared to Finland (2,300 mg/day for women and 3,100 mg/day for men).

MEASURING POTASSIUM LEVELS IN THE LABORATORY

The potassium balance and levels can be measured from blood plasma, serum, red blood cells, or whole blood. Potassium levels in the serum or plasma are used to monitor fluid and electrolyte balance and acid-base homeostasis. Elevated levels occur in connection with tissue damage (rhabdomyolysis, hemolysis), kidney deficiency, adrenal deficiency (Addison's disease), acidosis (where potassium is transferred from within cells to the space outside them), shock, tissue hypoxia, insulin deficiency, digoxin poisoning, and treatment involving spironolactone, amiloride or triamterene.

Low potassium levels occur due to the use of diuretics, fluid therapy containing insufficient potassium, dehydration due to diarrhea or vomiting, excessive use of laxatives, kidney disease (nephrites, tubular injury), alkalosis, primary and secondary hyperaldosteronism, Cushing's syndrome (hypercortisolism), excessive insulin intake, and magnesium deficiency.

Typical reference range (S-K):

Adults: 3.6–5.0 nmol/l

THE BEST FOOD SOURCES OF POTASSIUM (source: the Fineli database)

Dried fruits are rich in potassium but also high in sugar. Due to this, they are not included in this list.

Mineral salt (17,880 mg / 100 g), daily intake of 5 g contains 894 mg
Cocoa powder (3,490 mg / 100 g), raw cacao powder is recommended
Nori seaweed, dried (2,840 mg / 100 g)
Dark chocolate 80 % (1,754 mg / 100 g)
Pistachios (1,042 mg / 100 g)
Hemp seed, whole (859 mg / 100 g)
Pumpkin seeds (807 mg / 100 g)
Parsley (770 mg / 100 g)
Almonds (740 mg / 100 g)
Ground chicken meat (8.3 mg / 100 g)
Nettle (670 mg / 100 g)
Raisins (650 mg / 100 g)
Reindeer meat (621.6 mg / 100 g)
Parsnips (590 mg / 100 g)
Beef roast (566 mg / 100 g)
Cashews (565 mg / 100 g)
Golden chanterelles, fried (551.8 mg / 100 g)
Yellowfoot, fried (545.1 mg / 100 g)
Elk venison (535.9 mg / 100 g)
Fresh herbs, on average (501.5 mg / 100 g)
Potato peeled (500 mg / 100 g)
Radish (490 mg / 100 g)
Beetroot, oven-baked (484.3 mg / 100 g)
Rainbow trout (477 mg / 100 g)
Chard and spinach (470 mg / 100 g)
Rosehips (410 mg / 100 g)
Rolled oats (414 mg / 100 g)
Cauliflower (370 mg / 100 g)
Reindeer liver (370 mg / 100 g)
Sweet potato, oven-baked (366.3 mg / 100 g)
Champignon (364 mg / 100 g)
Banana, peeled (358.4 mg / 100 g)
Kiwi fruit, peeled (289.7 mg / 100 g)

Creatinine

Creatinine (Cr) is a waste product created using creatine phosphate in muscle energy production. Creatinine is constantly removed from the body via the kidneys by filtering it into the urine. Due to this, the creatinine levels in the serum are crucial when assessing kidney function.(63) Proper kidney function is critical in waste product removal, red blood cell production, bone metabolism, and blood pressure and fluid balance regulation.(64)

Healthy individuals' creatinine levels are proportional to their muscle mass and protein intake. High levels indicate impaired kidney function, which various reasons may cause. These include infections, autoimmune diseases, kidney inflammation, kidney stones, urinary tract obstruction, and medications such as ACE inhibitors. If the creatinine levels are high, a new blood test should be completed to confirm the result. Even slightly elevated creatinine levels can indicate severe kidney damage or disease.(65) Consistently high creatinine levels require medical treatment and follow-up tests.(66)

Low creatinine levels can indicate a low body muscle mass or protein intake. Insufficient creatinine levels are linked to increased mortality and lower survival rates, particularly for hospitalized patients. Such cases usually involve cachexia, a significant loss of muscle protein.(67)

Slightly elevated levels occur particularly in men with a large muscle mass and high protein intake from food and generally in connection with dehydration, without indicating a pathological change. In such cases, the cystatin-C marker (see later) is more precise when assessing kidney function.(68)

Approximately 10 % of the world's population has a chronic kidney disease of some type.(69) The two main risk factors for kidney deficiency are high blood pressure, hypertension, and diabetes.

Typical reference range (S-Cr):

Men: 60–100 umol/l
Women: 50–90 umol/l

Image: An artistic interpretation of Cystatin C.

Cystatin C

Cystatin-C is a protein produced by most cells in the body and filtered by the kidneys. Once filtered, it is broken down in the kidney's tubules.(70) Because Cystatin-C production is relatively constant and not influenced heavily by muscle mass, measuring Cystatin-C provides a more accurate kidney function assessment than creatinine alone.(71)

Elevated Cystatin-C levels typically indicate reduced kidney filtration. Causes can include infections, autoimmune conditions, kidney inflammation, urinary obstructions, and medication side effects that impair kidney blood flow. If a Cystatin-C test shows high levels, a repeat test can confirm any abnormality.(72) Persistently high Cystatin-C readings warrant medical evaluation and follow-up tests.(73)

Low Cystatin-C levels are usually less concerning than low creatinine levels. However, extremely low levels can reflect potential issues with protein metabolism or very low muscle mass, though this is less common. Additional assessments may be needed in hospitalized individuals or those with severe wasting conditions.

Mildly raised Cystatin-C can occur in older adults or those with mild dehydration. It does not always signify kidney disease. Reviewing hydration, medications, and overall health can help clarify the result's significance.(74)

Approximately 10% of people worldwide have some type of chronic kidney disease. The significant risk factors include high blood pressure and diabetes.

Typical reference range (S-Cystatin-C):

• Adults: 0.60–1.00 mg/L

Blood Urea Nitrogen (BUN)

Blood Urea Nitrogen (BUN) measures the nitrogen portion of urea, a waste product from protein metabolism. The liver converts ammonia, formed during protein breakdown, into urea, which is then released into the bloodstream and filtered by the kidneys.(75) BUN levels rise when kidney filtration declines or when protein breakdown increases. Similar to creatinine and cystatin-C, BUN is commonly used to assess kidney function alongside other markers.(76)

High BUN can indicate reduced kidney performance. Contributing factors include dehydration, high-protein diets, certain medications (like corticosteroids), and conditions that impair kidney filtration. In these instances, repeating the test can confirm whether the elevation persists. Persistently high BUN levels warrant medical follow-up to determine if the issue stems from acute kidney injury, chronic kidney disease, or other underlying problems.(77)

Low BUN levels are less frequent and can occur in malnutrition, severe liver disease, or low protein intake. If BUN is unexpectedly low, further testing is often recommended to examine liver function and overall nutritional status.(78)

Mildly elevated BUN can occur in individuals who consume large amounts of protein or experience temporary dehydration. Examining other kidney markers, such as creatinine or cystatin-C, helps confirm whether the rise is tied to a genuine kidney issue or caused by diet or fluid balance.(79)

Approximately 10-16 % of the global adult population has some form of chronic kidney disease, with significant factors including diabetes and high blood pressure.(80)

Typical reference range (BUN):

• Adults: 7–20 mg/dL (2.5–7.1 mmol/L)

Conclusion

Optimal kidney function relies on balanced fluid intake, mindful nutrient choices and attention to key markers like creatinine, cystatin-C, and blood urea nitrogen. These markers help assess how well the kidneys filter waste, regulate electrolytes, and stabilize blood pressure. When levels shift outside normal ranges, it may signal issues ranging from dehydration to chronic kidney disease.

Lifestyle steps such as moderate protein consumption, eating antioxidant-rich foods and sustaining regular physical activity protect kidney health. Adequate hydration assists in flushing toxins while avoiding harmful substances like smoking and excessive alcohol reduces extra strain. In conjunction, periodic screening allows for early detection of functional changes, helping guide timely interventions.

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