Providing your body with optimal hydration in the form of pure water is one of the simplest steps you can take to improve your health. It’s such a powerful tool that research published in the Journal of Clinical Investigation suggests 3 million fewer people in the U.S. would develop degenerative diseases if they improved hydration throughout life.1
It makes sense, since your body is made up mostly of water. At birth, body weight is 75% water, dropping to 55% in the elderly.2 Keeping an optimal balance between water intake and output is essential for survival, which is why if you become dehydrated, your body will activate a number of hormonal and neuroregulatory mechanisms to save your life.
Among them, you’ll begin to feel thirsty, reminding you to drink some water, while your kidneys hold onto water, so your urine output decreases.3
Researchers looked into the effects of long term subclinical hypohydration, or chronically losing more water than you take in, in mice and humans, finding evidence that even subtle changes in hydration levels led to “profound” effects on long-term health, and stating, “[W]e provide evidence from mouse and human studies that maintaining optimal hydration throughout a person’s lifetime provides protection from the development of age-dependent chronic disorders.”4
Restricted Water Intake Shortens Lifespan in Mice
For the first part of the study, mice had their water mildly restricted for a lifetime. While they easily adapted to the slightly lower water intake and showed no signs of distress, further testing revealed a state of chronic mild dehydration. Compared to mice with optimal hydration, the water restricted mice had a shortened lifespan and metabolic changes that led to increased food intake and energy expenditure.
During the first 12 to 14 months of life, the study also found that the water restricted mice had increased low-grade inflammation and coagulation, which could accelerate aging and act as indicators of age-related degenerative disease. By 14 months, the water restricted mice had faster declines in motor coordination.5 Further, the researchers noted:6
“We demonstrate that restricting the amount of drinking water shortens mouse lifespan with no major warning signs up to 14 months of life, followed by sharp deterioration.
Mechanistically, water restriction yields stable metabolism remodeling toward metabolic water production with greater food intake and energy expenditure, an elevation of markers of inflammation and coagulation, accelerated decline of neuromuscular coordination, renal glomerular injury, and the development of cardiac fibrosis.”
Not Enough Water Leads to Accelerated Aging and Degeneration
In the second part of the study, researchers analyzed data from 15,792 adults, using serum sodium concentration as a measure of hydration status and lifelong hydration. Participants whose serum sodium concentration was close to the upper end of normal had increased levels of risk factors for age-related morbidity and mortality.
Further, a strong association was found between serum sodium concentration in middle age and markers of coagulation and inflammation and the development of age-dependent degenerative diseases.
Like mice, humans with less-than-optimal hydration status had increased inflammation and other factors associated with degenerative diseases, including cognitive impairment, dementia, heart failure and chronic lung disease. High blood pressure and diabetes were also associated with hydration status.7 According to the study:8
“By analyzing disease prevalence, we showed that a serum sodium level below 142 mmol/L greatly reduced the risk for the development of many degenerative diseases including heart failure (HF), dementia, and chronic lung disease (CLD).
These findings indicated that serum sodium levels in the upper half of the ‘normal range’ should be treated as a clinical risk factor that prompts recommendation for modification of water and salt intake.”
Proper Hydration Could Spare Millions From Disease
Maintaining optimal hydration status during your life could lead to significant health benefits, but it’s difficult to define a set hydration level for everyone, since fluid needs vary according to activity levels, nutrition, health status and environment. However, the featured study suggested “a clear threshold of 141.5 mmol/L for serum sodium concentration,” above which the risk of age-related diseases goes way up.9
If everyone in the U.S. with sodium concentrations above this level were to decrease them by drinking more water, reaching the 140 to 141.5 mmol/L range, 3 million cases of related diseases could be spared. The researchers noted impressive benefits from improved hydration on a population-wide scale. Specifically:10
“These calculations predicted that the prevalence of dementia in people aged 70–85 years would decrease by 48%, HF by 24%, CLD by 20%, CKD by 10%, diabetes mellitus by 11%, high BP by 7%, and stroke by 3.1%. To estimate how many people would not develop these diseases as a result of such a preventive strategy, we extrapolated the results … to the whole population of the United States …
The calculations predicted that there would be about 342,000 fewer people with dementia, 353,000 fewer with HF, 597,000 fewer with CLD, 422,000 fewer with CKD, 442,000 fewer with diabetes mellitus, 822,000 fewer with high BP, and 59,000 fewer with stroke, in total decreasing the number of people aged 70–85 years with these diseases by 3,000,000 in the United States alone.”
Mental and Physical Health Risks of Dehydration
Your body needs water for blood circulation, metabolism, regulation of body temperature and waste removal. If you’re dehydrated, even mildly, your mood and cognitive function may suffer. In a study of 25 women, those who suffered from 1.36% dehydration experienced worsened mood, irritability, headaches and lower concentration and perceived tasks to be more difficult.11
A 2013 study in which 20 healthy women in their mid-20s were deprived of all beverages for 24 hours also showed the mental repercussions of too little water. While no clinical abnormalities were observed in the biological parameters (urine, blood and saliva), thirst and heart rate did increase and urine output was drastically reduced (and became darker).
As for mood effects, the authors noted, “The significant effects of [fluid deprivation] on mood included decreased alertness and increased sleepiness, fatigue and confusion.”12 This may be one reason why, in another study, dehydrated drivers were found to make twice the amount of errors during a two-hour drive compared to hydrated drivers.13
The No. 1 risk factor for kidney stones is also not drinking enough water, and there is research showing that high fluid intake is linked to a lower risk of certain types of cancer, such as bladder and colorectal.14
Even the risk of fatal coronary heart disease has been linked to water intake, with women who drank five or more glasses of water per day reducing their risk by 41% compared to women who drank less. Men, meanwhile, reduced their risk by 54%.15,16 Other symptoms of mild and severe dehydration include:17
|Mild to Moderate Dehydration||Severe Dehydration|
Dry, sticky mouth
Sleepiness or tiredness
Irritability and confusion
Dry skin that doesn’t bounce back when you pinch it
Low blood pressure
Few or no tears when crying
No tears when crying
Dry, cool skin
Little or no urination, and any urine color that is darker than usual
In serious cases, delirium or unconsciousness
Are You Drinking Enough Water?
Both children and adults often fail to drink enough water,18 and it’s estimated that 20% to 30% of older adults are dehydrated,19 often due to water deprivation and the fact that people naturally have a lower volume of water in their body as they get older.20
How much water is optimal varies depending on your age, health status, activity levels and more, but you might have heard the advice to drink eight 8-ounce glasses of water a day (known as the 8×8 rule).
This is not necessarily the best amount for everyone, as there is no one-size-fits-all water quota for humans. In fact, in a review published in the American Journal of Physiology, Heinz Valtin of Dartmouth Medical School in Lebanon, New Hampshire, could find no scientific basis for the 8×8 rule, which is more aptly described as a myth.21
Toby Mündel, senior lecturer at the School of Sport and Exercise, Massey University, New Zealand,22 recommends another method for monitoring your hydration levels: keeping track of your body weight. First thing in the morning when you get out of bed, weigh yourself for three mornings in a row, then calculate the average of your weights.
This is your normal baseline weight, and you should stay within 1% of that if you’re adequately hydrated (assuming other factors haven’t influenced your weight). Simply using thirst as a guide to how much water you need to drink is another way to help ensure your individual needs are met on a daily basis.
Optimal Hydration May Protect Your Health
You can also use the color of your urine as a guide. If it is a deep, dark yellow then you are likely not drinking enough water. A pale straw color or light yellow is typically indicative of adequate hydration. If your urine is scant or if you haven’t urinated in many hours, that too is an indication that you’re not drinking enough.
What is clear is that your body depends on a precise fluid balance to stay optimally healthy, and even slight changes in this balance can affect your physical and mental health. Even if you are only skimping on water slightly, it could be leading to accelerated aging or increasing the risk of degenerative disease, if the featured study is confirmed.
That doesn’t mean you need to stress over the proper amounts of water or force yourself to drink large quantities. Just be conscious of replenishing your body with pure water regularly, and definitely take a large drink if you’re feeling thirsty. Keep in mind that during strenuous physical activity, in hot climates and on long airplane flights,23 you may need more water than normal, so plan to keep your (reusable) water bottle handy.
Further, if you can’t remember the last time you’ve drank a glass of water, especially if you ordinarily reach for soda, energy drinks or fruit juice instead, make a point to switch your fluid of choice to pure water, and enjoy the health gains that follow.