Hydration - the real fountain of youth

‍Highlights:

• Proper hydration reduces the risk of kidney stones, urinary tract infections, hypertension, fatal coronary heart disease and other diseases
• Non-regulatory drinking causes excess calorie intake and poses a risk for obesity development
• Knowing what and how much to drink and spotting the signs of dehydration is crucial for longevity

Introduction

Hydration is an important topic in pursuit of longevity. Water is quantitatively the most important nutrient. Without water we would not survive for more than a few days but even a mild dehydration is a cause for concern as it can increase the risk of diseases. It is important to be able to recognize signs of dehydration as well as to know how to prevent it from happening. The modern western diet introduced a host of caloric beverages that promote drinking for reasons other than hydration. This poses yet another issue through excess calorie intake. The right choice of what to hydrate with is essential for longevity.

Dehydration promotes disease

Kidneys are the most directly impacted organs in the body when it comes to hydration. There is strong evidence showing that good hydration reduces the risk of kidney stones. In fact, a study looking at the French healthcare system found that if all patients adhered to fluid intake recommendations, it could prevent 11,572 new kidney stones and save €49 million in treatment costs (1). Unfortunately, the effects of sub-optimal hydration are not limited to kidneys. Here is an overview of the most notable issues associated with dehydration.

• Kidney function – Increased kidney stones risk.
• Gastrointestinal function – Increased risk of chronic constipation.
• Cognitive performance – Symptoms range from decreased concentration, alertness, and short-term memory to lower arithmetic ability, visuomotor tracking, and psychomotor skills.
• Physical performance – Increased risk for exercise induced asthma, reduced endurance, altered thermoregulatory capability, reduced motivation, and increased perceived effort.
• Headache – Dehydration increases the risk of headaches.

On the flip side, proper hydration is associated with a reduction in urinary tract infections, hypertension, fatal coronary heart disease, venous thromboembolism, and cerebral infarct (2).

Non-regulatory drinking poses a serious risk

Drinking that happens in response to signals of water deficit, such as physiological thirst, is called regulatory drinking. Its purpose is to regulate fluid balance in the body. People living in temperate climates such as North America or Europe often experience a second type of drinking which can be described as non-regulatory, its purpose is not to quench thirst. Non-regulatory drinking includes consuming fluids as components of everyday foods such as soup or milk, using them as mild stimulants like tea or coffee, and for pleasure and social interaction like alcohol, soda, and other sweetened beverages. An important thing to note is that many of these sources of fluid are high in calories and sugar. For example, a glass of full-fat milk has 12 g of sugar and 148 calories, a can of soda typically contains around 33 g of sugar and 138 kcal, a can of beer contains even more energy with 154 kcal. Plain black coffee contains virtually no calories but popular coffee-based beverages that include a lot of sugar and cream can carry as much as several hundred calories in one serving.

The increase in non-regulatory drinking that we are seeing in the developed western world may be advantageous because it allows water losses to be replaced before thirst-producing dehydration takes place. Unfortunately, it carries some disadvantages. Regular drinking of caloric fluids can contribute to an energy excess. Research confirms that water, when consumed in place of sugar-sweetened beverages, juice, and milk, is linked with reduced energy intake (2). Chronic caloric excess is the necessary prerequisite for weight-gain and subsequent development of obesity, metabolic syndrome, and type 2 diabetes.

Sports drinks are a special case, they can be considered part of regulatory drinking, they are used to optimize hydration. But they share similar risks with non-regulatory drinking. They have a very high sugar and calorie content and are commonly overused by amateur athletes. In excess, they pose an increased risk for tooth cavities, and could even contribute to metabolic problems.

Is the 8x8 rule evidence-based?

It is clear that preventing dehydration is important when low disease risk and longevity are the goals. Using non-regulatory drinking might be an effective solution but the unintended side-effect of increased calorie intake is too costly. This leaves people to follow the general recommendations for how much to drink. The 8x8 rule is probably the most recognizable one in the US. It tells people to drink 8 glasses containing 8 oz of water per day. In Europe, there is a similar general recommendation to drink about 2 liters of water daily. How accurate are these recommendations?

Based on available evidence, we can say that women need about 2.7 liters and men 3.7 liters of fluids per day. This includes fluids from water, other beverages, and from food. The assumption is that people get 20-30% of water from food. This means that women should be getting somewhere between 1.9 and 2.2 liters of fluids from water and men 2.6 to 3 liters. So, the 8x8 rule and 2-liter recommendations capture the minimum requirements relatively well. Research confirms that the 8x8 rule can be considered evidence-based (3). It is important to keep in mind that there are several factors that can change these water requirements. Nutritionists are well-placed to help their clients adjust these general recommendations to best fit their individual situation. These are the most important factors to consider.

• Diet – Eating a lot of fresh fruits and vegetables and soups can increase the proportion of fluid intake through food. High intake of salty, spicy, and sugary foods can increase the water intake requirements.
• Environment – Depending on season and daily temperatures and time spent outdoors, fluid requirements can change dramatically.
• Activity – Exercise as well as non-exercise activity such as walking or standing increase requirements.
• Health – People with acute conditions such as infection, fever, vomiting, or diarrhea will have increased requirements. Chronic conditions such as diabetes and taking drugs that promote glucosuria, such as gliflozins, also increase the amount of water needed.
• Pregnancy – Pregnant and breastfeeding women have increased fluid requirements. Depending on the age of the baby it could be more than 700 ml per day.

Some symptoms of dehydration are not well-known

Outside of exercise, it is generally ok to follow thirst signals as hydration cues. But not everyone is aware of all the symptoms to watch out for. Studies show that people living in hot climates are good at recognizing well-known signs of dehydration such as dry lips, dry tongue, dark yellow and strong-smelling pee, and thirst. But even they are not very good at recognizing the lesser-known symptoms including fatigue, lack of focus, headaches, dizziness, muscle weakness, rapid breathing, and muscle cramps (4).

On the other hand, it is good to keep in mind that overhydration is also dangerous. The literature documented deaths that have occurred as a result of overhydration, with resultant hyponatremia and cerebral edema. The reassuring thing is that all of those cases were associated with up to 20 liters of water intake within a few hours (5). It is unlikely that this would happen under normal conditions. In case of heavy sweating periods, it is safe to take in 1-1.5 liters of water per hour. It is essential to replenish electrolytes, mainly sodium, if sweating lasts for multiple hours.

Older people are at a higher risk of dehydration

Older people are more likely to run into issues with hydration even if they know how much and what they should be drinking (6). That is because they have lower thirst sensations and tend to drink less compared to younger adults (7). Research shows that young people take in almost twice as much fluid as old people following water deprivation, even though the older subjects have a much higher serum osmolality. Osmolality measures the concentration of dissolved particles in the blood. It’s used as a marker of dehydration because it reliably shows fluid loss when particle concentrations increase. It is important to urge older adults to drink water even when they are not thirsty. It is also helpful for them to limit beverages such as soda, coffee, and alcohol, which can worsen dehydration.

Conclusions

Proper hydration can significantly contribute to longevity through disease risk mitigation. It has been shown to reduce the risk of kidney stones, urinary tract infections, hypertension, fatal coronary heart disease and other diseases. It can improve quality of life through better cognitive and physical performance. The key to unlocking these benefits is focusing on sufficient water intake while reducing non-regulatory drinking of caloric beverages. Nutritionists are well-placed to help their clients identify their individual optimal water intake and reinforce the habit, especially in older individuals who are at a higher risk for chronic dehydration.

References

1) Y Lotan, I Buendia Jiménez, I Lenoir-Wijnkoop, M Daudon, L Molinier, I Tack, M J C Nuijten. Increased water intake as a prevention strategy for recurrent urolithiasis: major impact of compliance on cost-effectiveness. J Urol . 2013 Mar;189(3):935-9. doi: 10.1016/j.juro.2012.08.254.

2) Barry M. Popkin, Kristen E. D’Anci, Irwin H. Rosenberg. Water, Hydration and Health. Nutr Rev. 2010 Aug; 68(8): 439–458. doi: 10.1111/j.1753-4887.2010.00304.x

3) Jodi D Stookey, Stavros A Kavouras. Water Researchers Do Not Have a Strategic Plan for Gathering Evidence to Inform Water Intake Recommendations to Prevent Chronic Disease. Nutrients. 2020 Oct 31;12(11):3359. doi: 10.3390/nu12113359.

4) Naila A. Shaheen, Abdulrahman A. Alqahtani, Hussam Assiri, Reem Alkhodair, Mohamed A. Hussein. Public knowledge of dehydration and fluid intake practices: variation by participants’ characteristics. BMC Public Health . 2018 Dec 5;18(1):1346. doi: 10.1186/s12889-018-6252-5.

5) John W. Gardner. Death by Water Intoxication. Military Medicine, Volume 167, Issue 5, May 2002, Pages 432–434, https://doi.org/10.1093/milmed/167.5.432

6) Miyuki Shimizu et al. Physical signs of dehydration in the elderly. Intern Med. 2012;51(10):1207-10. doi: 10.2169/internalmedicine.51.7056. Epub 2012 May 15.

7) Robert D Meade, Sean R Notley, Maura M Rutherford, Pierre Boulay, Glen P Kenny. Ageing attenuates the effect of extracellular hyperosmolality on whole-body heat exchange during exercise-heat stress. J Physiol. 2020 Nov;598(22):5133-5148. doi: 10.1113/JP280132. Epub 2020 Sep 29.

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