Dangers of dehydration from popular foods and drinks

By Naveed Saleh, MD, MS
Published October 29, 2020

Key Takeaways

Although dehydration is common, the dangers that it poses are likely underappreciated. It’s linked to health risks such as thromboembolism, infectious disease, urolithiasis, and obstipation. These risks are most pronounced in the elderly.

Lack of thirst, changes in body mass, decreased renal function, drug interactions, and disturbances in water/sodium balance can all contribute to dehydration risk. Also, what you eat or drink can actually make things worse. 

Here are four foods and drinks that dehydrate, thus exacerbating alterations in water/sodium balance. Plus, there’s one that many people think causes dehydration, but actually doesn’t. 

Sugar-sweetened beverages

Recurrent dehydration, which is common among manual laborers in hot climates, can lead to chronic kidney damage induced by the effects of hyperosmolarity. More specifically, this hyperosmolarity activates both vasopressin and aldose reductase-fructokinase pathways, with sugar sweetened-beverages like soft drinks likely responsible for triggering the latter pathway, according to authors of a study published in American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.

In this preclinical study, the researchers recurrently dehydrated rats for 4 weeks by exposing them to heat (36°C/96.8°F) for 1 hour daily, which was followed by 2 hours of access to plain water, an 11% fructose-glucose solution (similar in composition to a soft drink), or Stevia-sweetened water. They then analyzed plasma and urine samples, and assessed the kidneys for markers of oxidative stress, injury, and inflammation.  

“Rehydration with 11% [fructose-glucose] solution, despite larger total fluid intake, resulted in greater dehydration (higher osmolarity and copeptin levels) and worse renal injury, with activation of aldose reductase and fructokinase, whereas rehydration with stevia water had opposite effects,” the authors wrote.

“In animals that are dehydrated, rehydration acutely with soft drinks worsens dehydration and exacerbates dehydration associated renal damage. These studies emphasize the danger of drinking soft drink-like beverages as an attempt to rehydrate following dehydration,” the authors concluded.

Alcoholic beverages

Alcoholic beverages have long been known to cause diuresis, which can, in turn, lead to dehydration. These effects could be due to small metabolites passing through the renal glomerulus and causing osmotic diuresis in the urine. Alternatively, alcohol can inhibit the release of the antidiuretic hormone vasopressin, according to a classic JAMA study.

Publishing in Nutrients, researchers examined the diuretic effects of moderate-alcohol consumption in elderly men. Moderate consumption was defined as fewer than 21 alcoholic drinks per week, at 10 g of alcohol per drink. They assessed the effects of both weak and strong alcoholic beverages on dehydration biomarkers.

“Only moderate amounts of stronger alcoholic beverages (≥13.5%) resulted in a temporary diuretic effect compared to their non-alcoholic counterparts,” they noted. “AB [alcoholic beer] and NAB [non-alcoholic beer] did not differ at any time point in terms of the urine output, osmolality, and sodium and potassium concentration.”

“This suggests that the consumption of moderate amounts of a weak alcoholic beverage such as beer is safe in terms of hydration for elderly men,” they wrote. “Taking the results of previous studies into account, it seems that moderate amounts of weak alcoholic beverages do not negatively influence hydration status, but when the alcoholic strength and serving size increases, so does the acute diuretic effect.”

In other words, in older men drinking only moderate amounts of stronger alcoholic beverages, dehydration risk is minimal and short-lived. More excessive drinking, however, will likely dehydrate to a greater extent, they concluded.

Protein

The popularity of high-protein diets has climaxed in recent years, but high-protein intake could lead to dehydration.

Researchers assessed the relationship between protein intake and hydration indices in a 3-month crossover study published in the Journal of the American Dietetic Association to evaluate effects on endpoints including blood urea nitrogen, plasma osmolality, urine-specific gravity, and estimates of fluid balance. 

They found that in male athletes on eucaloric diets, although measures of fluid intake/balance and fluid status were no different, blood urea nitrogen and plasma osmolality were higher for athletes consuming a high protein diet (3.6 g/kg/day) than those consuming moderate protein (1.8 g/kg/day) or low protein (0.8 g/kg/day) diets. Furthermore, urine-specific gravity was higher for high protein vs moderate protein diets.

“Based on our findings, we believe that it is important for athletes and non-athletes alike to increase fluid intake when consuming a high protein diet, whether they feel thirsty or not, because our study subjects said they did not feel a difference in thirst from one diet to the next,” said corresponding author Nancy R. Rodriguez, PhD, RD, associate professor in the Department of Nutritional Sciences, University of Connecticut.

Coconut water

Drinking some cool coconut water while exercising may sound refreshing. But this beverage choice may be dehydrating—and not for the reasons you may think.

In a small experimental study published in the International Journal of Sport Nutrition and Exercise Metabolism, researchers examined rehydration markers in cyclists completing 60-min of submaximal cycling followed by a 10-km time trial on two occasions. Although markers including body mass and urine osmolality did not change after hydration with either pure or coconut water, cyclists found coconut water was less palatable and elected to drink less during the experiment. 

Lesson here: Save your money and cut down on calories by ditching the coconut water in favor of plain old water, which likely tastes better.

Caffeine

Caffeine found in beverages and foods have a well-known diuretic effect, so coffee-drinkers and other caffeine consumers are often warned to consume less at times when fluid balance may be compromised—such as working outside for long hours or running 10 miles on a hot day. 

It turns out, such warnings may be unnecessary. 

According to a review article published in the Journal of Human Nutrition and Dietetics, consuming caffeine equivalent to the amount found in 2 or 3 cups of coffee (or 5-8 cups of tea) does cause a short‐term increase in urine output—but only in people who haven’t had any caffeine for several days or weeks. 

“A profound tolerance to the diuretic and other effects of caffeine develops, however, and the actions are much diminished in individuals who regularly consume tea or coffee,” the authors wrote. In fact, regular caffeine consumption at “standard servings” appears to have no diuretic action.

“The most ecologically valid of the published studies offers no support for the suggestion that consumption of caffeine‐containing beverages as part of a normal lifestyle leads to fluid loss in excess of the volume ingested or is associated with poor hydration status. Therefore, there would appear to be no clear basis for refraining from caffeine containing drinks in situations where fluid balance might be compromised,” the researchers concluded. 

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