Are sports drinks good for you?
Talking of marathons, today there are many advertisements of sports drinks which claim to re-hydrate you when you run or exercise or play intense sports.
Sports drinks are advertised to replenish glucose, fluids, and electrolytes (sodium, potassium, magnesium, calcium) lost during strenuous exercise. They also claim to enhance endurance. Some brands also contain B vitamins associated with increased energy (not to be confused with energy drinks, which are a different product entirely). What is the verdict on such drinks? Are they really good for you?

What's inside them
Sports drinks usually contain carbohydrate in the form of sugar (e.g., glucose, high-fructose corn syrup, sucrose) or contain no sugar and are flavored instead with low-calorie sweeteners.
Sports drinks can be split into three major types:
. Isotonic sport drinks contain similar concentrations of salt and sugar as in the human body.
. Hypertonic sport drinks contain a higher concentration of salt and sugar than the human body.
. Hypotonic sport drinks contain a lower concentration of salt and sugar than the human body.
Most sports drinks are approximately isotonic, having between 4 and 5 heaped teaspoons of sugar (13-19 grams) per 250ml serving. The specific amount of sugar and electrolytes in sports drinks is intended to allow for quick hydration and absorption when you lose nutrients during intense work-outs. This type of nutrient loss generally occurs only with high-intensity exercise that lasts an hour or more. For the non-athlete, a sports beverage is just another sugary drink!

BOX on Energy drinks versus Sports drinks
Sport drinks are flavored beverages with high calorie content that often contain carbohydrates, minerals and electrolytes and sometimes other vitamins and nutrients. They may have some benefit for the young athlete who participates regularly in endurance or high intensity sports when used in addition to plain water for hydration.
Though sometimes confused with sports beverages, energy drinks are a different product entirely. They are marketed to increase alertness and energy levels, containing significant amounts of caffeine and as much or more sugar as in soda. Many energy drinks pack about 200 mg of caffeine, the amount in two cups of brewed coffee. According to a recent study, some energy drinks can have as much as 14 times the amount of caffeine found in the average cola product. Other substances purported to increase energy may be added, like B vitamins and herbs such as ginseng and guarana. Most concerning is a lack of regulation about the safety of these drinks, as well as aggressive marketing tactics geared toward adolescents.
Sipping a beverage that offers quick energy may appeal to people who feel fatigued or who believe the caffeine can provide an edge when exercising or playing competitive sports. Although statements on the websites of energy drinks warn that these beverages may not be suitable for children, youth are among their largest consumers. An energy drink may be used by adolescents or college students cramming for exams through the night, or by a young athlete before an important game.
Some controlled trials have shown temporary improved alertness and reversal of fatigue after taking energy drinks, as well as enhanced physical performance in young athletes. But the majority of studies show an association with negative health effects. These include increased stress, aggressive behaviors like fighting, alcohol/cigarette abuse, increased blood pressure, increased risk of obesity and type 2 diabetes, poor sleep quality, and stomach irritation.
The amount of caffeine can lead to difficulty sleeping, headaches, difficulty in concentrating, anxiety, and irregular heartbeat. Depending on the amount of stimulant in the beverage, over-use can cause toxicity and even death. There is even the risk for physical dependence and addiction to the stimulants in these beverages. Therefore energy drinks are never recommended for children or adolescents.
END OF BOX

Sports Drinks and Health
Research has shown benefit of sports drinks in adult athletes (though not conclusive as some studies show no benefit), but research in children is lacking. Children sweat at highly variable rates, so it is more difficult to establish an amount of exercise time for which the drinks may be useful.
A study in the USA showed that 26% of sugar-sweetened drinks taken by children and youth are sports drinks. Sports drinks contain less sugar than soda and energy drinks, but still contain simple sugars. For example, a 300 ml cola drink contains about 39 grams of sugar, compared with 21 grams of sugar in a popular sports drink. Drinking too many of these, especially when not performing vigorous exercise, can increase the risk of overweight/obesity and other health problems such as type 2 diabetes, cardiovascular disease, and gout. There is also a risk of dental caries due to the amount of sugar.
Another study in the USA followed more than 4,100 females and 3,400 males for 7 years as part of a Growing Up Today Study. They found that the more frequently sports beverages were consumed, the greater the association with an increased body mass index leading to overweight/obesity. This was true especially for boys, very likely because these drinks are endorsed on social media by sports celebrities. Also, children may drink them excessively, thinking that they are good for health.

Bottom Line
The final word perhaps comes from the Harvard T.H. Chan School of Public Health. They state: "Water that is calorie-free and accessible without cost to most people is the beverage of choice taken with and between meals. A sports drink may be used by people engaging in exercise of vigorous intensity for more than one hour, especially if sweating heavily. Perhaps of greater importance in athletes of any age, but especially youth, is to encourage a balanced diet, snacks as needed, and adequate water that will best enhance physical and mental performance."

Sources: https://www.hsph.harvard.edu/nutritionsource, Wikipedia