Staying adequately hydrated is critical for maintaining kidney health and overall well-being. The kidneys are vital organs that filter waste from the blood, regulate blood pressure, and produce essential hormones. Dehydration can impair these functions, leading to various health issues.

The kidneys act as a continuous, high-tech water filter for the blood. They process up to 150 quarts of blood every 24 hours to produce 1-2 quarts of urine. Proper hydration is essential for this filtration process to function efficiently. When the body is dehydrated, the kidneys must work harder to filter waste, potentially leading to damage over time.
Waste Removal:Â Kidneys filter metabolic waste products from the blood. When you are dehydrated, waste products can accumulate in the blood and cause symptoms like weakness, shortness of breath, confusion, and abnormal heart rhythms.
Kidney Stone Prevention:Â Proper hydration helps dilute urine, reducing the concentration of substances that form kidney stones. When urine is more alkaline, stones are less likely to form.
Blood Pressure Regulation: The kidneys play a role in regulating blood pressure. Dehydration can affect blood volume and, consequently, blood pressure.
Overall Kidney Health:Â The diets that are healthiest for our hearts, centered around unprocessed plant foods, may be the best way to prevent and treat kidney disease.
How Dehydration Impacts the Kidneys
Dehydration can have several detrimental effects on kidney health:
Reduced Filtration Efficiency:Â When the body is dehydrated, the kidneys may struggle to filter blood effectively, leading to a buildup of toxins.
Increased Risk of Kidney Disease:Â Chronic dehydration can contribute to the development and progression of kidney disease. A national survey found that only 41% of Americans tested had normal kidney function, a drop from 52% a decade earlier.
Kidney Damage:Â Dehydration may force the kidneys into a state of hyperfiltration, which is a dramatic increase in workload. Over time, this unrelenting stress can lead to a decline in kidney function.
Metabolic Acidosis: Dehydration may be linked to metabolic acidosis, which is often attributed to a diet high in meat. This can cause damage to the urine-making tubes in the kidneys.
Increased Risk of Kidney Stones:Â When you don't drink enough water, the urine becomes concentrated, which may lead to kidney stones. Kidney stones are hard mineral deposits that form when the concentration of certain substances in the urine is high.

Recognizing Dehydration
It is important to be able to recognize the signs of dehydration:
Urine Color:Â The color of urine can be an indicator of hydration levels. The gold standard for hydration is the color of straw, a light yellow. A darker yellow or brownish color may indicate dehydration. However, this method may not be reliable in older adults.
Fatigue and Missed Drinks:Â In older adults, the combination of experiencing fatigue and missing some drinks between meals is an indicator of dehydration.
Body Signals:Â If you drink water and your body quickly eliminates it, you are likely well-hydrated. If your body holds onto most of the water, you may be dehydrated.
Formal Dehydration Assessment:Â A formal assessment can be done by emptying the bladder, drinking three cups of water, and then checking how much is urinated within an hour. If less than one cup is urinated, then dehydration is likely.
Brain Shrinkage: When you become dehydrated, your brain actually shrinks.
How Much Water is Enough?
General Recommendations:Â Authorities from the World Health Organization and the U.S. Institute of Medicine recommend about 8 to 11 cups of water a day for women and 10 to 15 cups a day for men.
Water from all sources: These recommendations include water from all sources, not just beverages. We get about four cups of water from the food we eat and what our body produces. This translates to a daily recommendation of 4-7 cups of water for women and 6-11 cups for men, assuming moderate physical activity.
Individual Needs:Â Water needs can vary based on factors such as age, activity level, and climate.
Avoid Overhydration: The kidney capacity of older individuals is approximately three to four cups per hour. Avoid exceeding this limit to avoid diluting electrolytes in the brain.
Five Glasses a Day:Â It is generally recommended to drink five glasses of water a day.
Water From Other Beverages:Â Water can also be obtained from other drinks, such as coffee and tea, but the health benefits seen in studies are mostly associated with increased consumption of water. Stronger alcoholic drinks like wine can actually dehydrate you.
Additional Tips for Staying Hydrated
Drink Throughout the Day: Do not wait until you feel thirsty to drink water. Drink water consistently throughout the day.
Tap Water: Choose tap water when possible. It is less expensive and may have less chemical and microbial contamination than bottled water.
Avoid Sugary Drinks: Limit consumption of sugary drinks, such as soda and juice.
Monitor Fluid Intake:Â If you have a condition such as heart or kidney failure, or your doctor advises you to restrict fluid intake, follow their recommendations.
Eat Hydrating Foods:Â In addition to drinking water, consume foods with high water content such as fruits and vegetables.
Hydration and Cognitive Function: Staying hydrated may elevate your mood and improve your thinking. Dehydration can cause the brain to shrink, which can impair function.
Dehydration and Other Health Issues
In addition to kidney health, dehydration can affect other bodily functions:
Increased risk of falls and fractures.
Heat stroke.
Heart disease.
Lung disorders.
Bladder and colon cancer.
Urinary tract infections.
Constipation.
Dry-eye disease.
Cavities.
Decreased immune function.
Cataract formation.
May decrease alertness, happiness, and clarity of thought.
The Myth of "Eight Glasses a Day"
The oft-quoted recommendation to drink at least eight glasses of water a day has little scientific evidence to support it. This recommendation can be traced back to a 1921 paper that measured one person's urine and sweat output, and then used that to make a generalization about water needs. Current recommendations are based on better evidence.
Water and Mortality
Some studies have shown a link between increased water consumption and decreased mortality, while others have not. This means the connection is still unclear. However, drinking five or more glasses of water a day may cut your risk of dying from heart disease in half. Also, a high intake of water may reduce the risk of bladder cancer by about 50%.
Special Considerations for Older Adults
Older individuals may only be about 50% water, compared to 70% for newborns. They have smaller fluid reserves, a diminished sense of thirst, and a reduced ability of their kidneys to concentrate urine, which makes them particularly vulnerable to dehydration. It is also difficult to assess hydration in older adults, because common methods like urine color may not be reliable.
Conclusion
Staying adequately hydrated is essential for maintaining healthy kidney function and overall well-being. Proper hydration helps the kidneys efficiently filter waste, prevents kidney stone formation, regulates blood pressure, and supports numerous other bodily functions. By drinking enough water throughout the day and being aware of the signs of dehydration, you can take proactive steps to protect your kidneys and improve your overall health.
ReferencesÂ
Greger, M., & Stone, G. (2015). How not to die: Discover the foods scientifically proven to prevent and reverse disease. Flatiron Books.
Greger, M. (2023). How not to age: The scientific approach to getting healthier as you get older. Flatiron Books.
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