What’s your go-to hydration beverage? Good hydration is a must for optimal exercise performance and safety. Even mild dehydration can stymie your exercise performance and impede recovery from exercise. What you rehydrate with matters too. Have you ever reached for a caffeinated soft drink to stave off dehydration? At one time, the maker of Coke claimed their soft drinks are good hydration beverages. However, a new study suggests that caffeinated, sugar-sweetened soft drinks are a bad choice for supplying your body with liquid during a workout, especially if it’s warm outside.
What a Study Showed about Soft Drinks and Kidney Health
Researchers asked a group of healthy adults to take part in an exercise session in a hot environment (temperature of 95 degrees F). During the first 30 minutes, the participants walked on a treadmill for 30 minutes. Then, the participants did 15 minutes of different exercises that required strength and power, such as lifting and swinging a sledgehammer. The goal of the exercise was to mimic the type of work people do on a hot day at a construction site.
After 45 minutes of exercise, the subjects drank 16 ounces of water or a fructose-sweetened soft drink with caffeine. The composition of the beverages was typical of what a soft drink you buy at the supermarket contains. The subjects completed three more sessions and again drank their designated beverage for rehydration. After a week, they switched so that the subjects drink the opposite drink to the one they drank during the first trial. The soft drink drinkers now drank water and vice versa. The researchers measured markers including blood pressure, heart rate, body temperature, and markers of kidney function before and after each trial.
What did they find? Not only did the caffeinated, fructose-sweetened drinks not rehydrate the subjects well, but the participants who drank them also had changes in markers of kidney function. In fact, their kidney function declined temporarily when they rehydrated with the soft drink beverages. These changes were short-term but any change raises red flags. What if you routinely drink these beverages when you exercise in a hot environment? Could the effects long-term be harmful? The results show that we need to study the impact of drinking beverages sweetened with fructose that contains added caffeine on the kidneys during exercise, especially since so many people drink them.
This isn’t the first study to show that soft drinks and other carbonated beverages aren’t good for the kidneys. One study found that people who drank at least 2 carbonated beverages daily excreted more protein into their urine. More protein in the urine is linked to reduced kidney function. In fact, a 2007 study found that drinking 2 or more cola, but not non-cola beverages, was linked with a higher risk of kidney disease. Cola beverages contain more phosphoric acid than non-cola beverages whereas non-cola beverages are higher in citric acid. Phosphoric acid can combine with calcium and form calcium phosphate deposits. These deposits may attach to portions of the kidneys and damage the kidneys.
Avoid Soft Drinks if You Have Kidney Stones
Kidney stone sufferers should also steer clear of soft drinks and other sugar-sweetened beverages. In an Australian study, researchers looked at the association between various types of beverages and the incidence of kidney stones. The study summarized data from three large studies involving over 194,000 participants. The consensus was that drinking even one sugar-sweetened beverage daily boosted the risk of kidney stones by 23 to 33%. The best beverage to drink to lower the risk of kidney stones is water with a squirt of lemon. The citric acid in the lemon lower the pH of the urine and this makes it harder for kidney stones to form.
Need another reason to skip soft drinks? Do it for your bones. As mentioned, darkly colored soft drinks, like colas, contain phosphoric acid. If you consume a higher ratio of phosphoric acid to calcium, it can trigger bone loss. When you throw caffeine into the mix, the impact may be even greater. Some studies suggest that caffeine reduces calcium absorption, another negative for bone health.
It’s likely that energy drinks fall into this category too. Many contain similar ingredients, such as high fructose corn syrup, that soft drinks do. They’re fizzy drinks just like a can of cola! A study showed that, in some people, energy drinks alter conduction through the heart in such a way that it makes irregular heart rhythms more likely to occur. Energy drinks often contain additional herbal stimulants other than caffeine. There have been reports of a variety of adverse effects of energy drinks on the heart, including heart attack, irregular heart rhythms, and even death.
The Bottom Line
There’s no shortage of reasons not to drink soft drinks, but now it appears they aren’t a good rehydration beverage either. At least short-term, they negatively affect kidney function. It’s hard to generalize this to all workouts since the study mimicked conditions of doing manual labor for around four hours in a hot environment. Most workouts are shorter and carried out in a cooler environment. But it does raise questions about popping the tab off a can of cola and using it to rehydrate after a workout.
Unless you’re exercising for 90 minutes or longer. Clean water, possibly with a squirt of lemon, will suffice. If you’re exercising longer, consider sipping on a beverage that contains electrolytes. Even then, go the natural route. Coconut water is a potassium-rich drink and if you add a pinch of salt, you’ll replace lost sodium as well. In fact, coconut water contains more potassium than the average sports drink.
Take hydration seriously but choose your hydration beverage wisely. Now, you know why soft drinks, especially cola drinks and carbonated beverages aren’t a good choice.
References:
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2019; DOI: 10.1152/ajpregu.00351.2018.
WebMD.com. “Soda and Osteoporosis: Is There a Connection?”
Am J Clin Nutr. 2006 Oct;84(4):936-42.
LiveScience.com. “Why Coconut Water Could Replace Your Sports Drink”
Epidemiology. 2007 Jul; 18(4): 501–506. doi: 10.1097/EDE.0b013e3180646338.
Kidney Health Australia. “The Association between Sugar-Sweetened Soft Drink and Chronic Kidney Disease A Position Statement”
Cureus. 2017 Jun; 9(6): e1322.
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