After exercise, people like to refresh themselves with a soft drink. Not a good idea, as a New York study, showed, because the drinks have been shown to damage the kidneys and lead to ongoing dehydration.
Soft drinks are bad for the kidneys
Soft drinks are anything but healthy. They often contain caffeine, flavorings as well as sugar, fructose-glucose syrup, or sweeteners. In the meantime, they are held responsible for the increasing number of overweight and diabetic people worldwide.
In January 2019, researchers from New York University at Buffalo were able to show that sweet drinks can also impair kidney health if you drink them during or after training. The study appeared in the American Journal of Physiology.
Soft drinks dehydrate
Earlier studies from the 1990s ( 4 ) already showed that exercise – when practiced in summer at high temperatures – increased those blood values that normally only rise when the kidneys have a problem.
At the same time, there were studies (e.g. from July 2016) in which it could be shown in rats that soft drinks with a high fructose content increase the risk of kidney damage if the animals were very thirsty, i.e. already dehydrated.
The New York researchers now linked these two theses in their study. They wanted to find out how soft drinks – compared to water – changed the kidney values of dehydrated athletes during summer training.
Study: How do soft drinks affect exercise?
12 healthy and athletic adults with an average age of 24 made themselves available as participants. They completed a 30-minute workout on the treadmill and then did 15-minute exercises designed to simulate physical farm labor.
After the 45-minute workout, participants rested for 15 minutes while receiving either a popular caffeinated and flavored high-fructose soft drink or water. In total, they repeated this 1-hour routine four times, so the participants trained a total of four times for 45 minutes each and then rested for 15 minutes each time. During the break, there was always the appropriate drink.
A week later the same event took place again, but this time the groups were switched. Those athletes who had previously received the soft drink now drank water and vice versa.
Kidney values deteriorate after soft drink consumption
Blood samples were of course also taken regularly on the training days – before the training, immediately afterward, and also 24 hours afterward. They tested the creatinine levels and the glomerular filtration rate – both are markers that can detect kidney damage. Heart rate, body temperature, body weight, and blood pressure were also checked.
As expected, both kidney-relevant blood values were increased in the soft drink groups. Additionally, soft drink consumers were mildly dehydrated and had higher vasopressin levels. Vasopressin is a hormone that raises blood pressure and at the same time ensures that the body loses as little water as possible in the urine, so increased vasopressin levels also indicate dehydration.
Never drink soft drinks during sports or physical work!
So if you think you can keep yourself hydrated with soft drinks after your summer workout, you’re wrong. Soft drinks do not completely rehydrate, in fact, they leave the body in a dehydrated state.
Of course, these results do not only apply to athletes who train in the heat, but also to people who (have to) do physical work in high temperatures. Basically, you should quench your thirst – no matter which group of people you belong to – preferably with water.
Especially in summer or when you sweat a lot, train a lot or even take part in competitions and sometimes drink a lot of water, you should avoid water that is low in minerals and instead enrich the water with minerals or a little sea or rock salt. Occasionally coconut water can also be used as a high-quality isotonic thirst quencher.
Update September 2022 – Soft drinks damage the kidneys even without exercise
Even without exercise or strenuous work, soft drinks damage the kidneys (if they contain sugar) and increase the risk of chronic kidney failure, as a 2014 review found. The soft drinks were decaffeinated. Artificially sweetened soft drinks did not show an increased risk of chronic kidney disease in this study.