Many popular sports drinks and other thirst-quenchers spell trouble for athletes’ mouths. John Banky explains.
Any athlete performing at a high level understands the importance of maintaining good hydration. In practice this can sometimes be hard to impossible to achieve: the wrong combination of heat, humidity and tough competition can undermine the most meticulous preparation. One notable hot, humid night in Melbourne in 2001 provided exhausting and punishing conditions for the semifinal match of the Australian Tennis Open between Pat Rafter and Andre Agassi. Rafter, a super-fit serve-volleyer, was reduced to a walk by severe cramps during the match and was rehydrated afterwards with a saline drip.
The more intense and sustained the activity, the greater the need for fluid replacement. Apart from tennis, endurance events such as marathon, triathlon, some cycling events and even cricket matches can all last several hours, requiring participants to replace fluid loss by drinking at frequent intervals.
Sports drinks which are widely available today were initially made to help with hydration and nutrient balance. The body absorbs water and nutrients (1) in the upper part of the small intestine. Nutrients such as glucose, which is cotransported with sodium, increase the intestine’s water absorption, but the main determinant of how rapidly water and nutrients are absorbed is gastric emptying, which is affected by the volume of fluid in the stomach.
During physical activity a large volume of fluid is lost which is hard to replace in one go by drinking. Sport supplement drinks now often contain additives that speed up their absorption in the digestive system. These drinks are an increasingly popular choice for athletes to help them maintain good hydration; but their use comes at a price: dental erosion.
Tooth surface damage occurs as a result of acid in contact with the tooth surface. When this contact is frequent, the tooth surface may be damaged permanently. Acid in contact with the tooth surface (2) can be from:
The relationship between acid levels (pH) at the tooth surface and time following consumption of food and drink is shown in what is known as the Stephan Curve (3) (see fig 1 below). A low pH indicates acidic conditions; a high pH shows alkalinity. When the pH at the tooth surface is below 5.5 (critical pH) tooth surface damage occurs.
The Stephan Curve shows an increase in acid accumulation at the tooth surface (a drop in pH) immediately after we eat or drink something. After swallowing, saliva dilutes what remains in the mouth, reducing the potential for tooth surface damage. It takes approximately 20 minutes for the saliva to do its job of diluting and washing away the erosive liquid in contact with the tooth surface until the pH exceeds 5.5.
Frequent drinking during exercise is the best protection against net fluid loss. But the Stephan Curve also shows that frequent drinking/eating prolongs the period of time that the pH at the tooth surface remains below the critical value of 5.5. And the risk to teeth is compounded if the flow of saliva is reduced for any reason. This can be a short-term effect of dehydration or certain medications; or a long-term consequence of habitual mouth-breathing or damage to a salivary duct or gland.
There are three main ways in which the risk of dental erosion is greater among athletes trying to maintain good hydration levels than among the general population (2,4,5,6). These are:
We know from research that the pH level of a drink has a minimal effect on the body’s capacity to absorb it (1). So why do most sport drinks and carbonated drinks have a pH of 2.4-4.5? The answer is that the acidity improves the taste and increases the shelf life of the products. Another way to reduce the risk of dental erosion would be to add calcium (7), but this also tends to reduce the pleasantness of the taste (10).
|Isostar (sports drink)||2.38||5|
|Maxim (sports drink)||4.46||5|
|Gatorade (sports drink)||3.3||11|
John Banky is a general dental practitioner with an interest in dental injury and injury management away from the dental surgery. He is a member of Sports Medicine Australia and The Autsralian Dental Association