Soft drinks (carbonated beverages, soda pops) have no significant nutrient value and are high in calories, sugar and contain food additives such as caffeine, colours and flavours. Excessive consumption of soft drinks has been linked to obesity, tooth decay, weak bones and caffeine addiction. However, compared with the data available on tobacco and dietary fat, the scientific evidence on soft drinks is less developed.
A survey of 100 UK children showed that 70% of pre-school and 50% of infant school children never drank plain water. Half of the pre-school children obtained 50% of their recommended daily energy intake from soft drinks.
Soft drinks account for more than a quarter of all drinks consumed in the USA. More than 56,780 million litres were sold in 2000 - equivalent to at least one 1/3 litre can per day for every man, woman and child. Carbonated soda pop provides more added sugar in a typical 2-year-old's diet than biscuits, sweets and ice cream combined. Fifty-six percent of 8-year-olds have soft drinks daily, and a third of teenage boys drink at least three cans (one litre) of soft drink per day. On average, US teenagers drink about half a litre of of carbonated beverages each day.
In 1998, teenage boys and girls in the USA drank twice as much carbonated soft drinks (mainly cola) as milk, whereas in 1968 they drank nearly twice as much milk as soft drinks. About 61 percent of teenagers reported drinking carbonated beverages on any given day (2000), compared with just half who drink milk; only one in every five met the current milk requirement.
A federally funded study of nearly 3,200 Americans 9 to 29 years old conducted between 1971 and 1974 showed a direct link between tooth decay and soft drinks. Numerous other studies have shown the same link throughout the world, from Sweden to Iraq. But in the last 25 years, tooth decay in developed countries has actually declined -- at the same time that soft drink use and obesity have risen dramatically. This has been explained by the importance of other factors in reducing tooth decay, such as improved diet and fluoridated water. The acids in soft drinks etch tooth enamel in ways that can lead to cavities. Acid begins to dissolve tooth enamel in only 20 minutes.
Drinking soda is now considered to be "an independent risk factor for obesity; however explanations of the mechanism by which soda may lead to obesity have not yet been proved, though the evidence for them is strong. For example, a US study showed that 12-year-olds who drank soft drinks regularly were more likely to be overweight than those who did not. For each additional daily serving of sugar-sweetened soft drink consumed during the nearly two-year study, the risk of obesity increased 1.6 times.
Caffeine is a psychoactive substance that affects the brain. It is present not only in colas but a number of other soft drinks, including some fruity ones drunk mainly by children. In one study, 8- to 12-year-old children were given the equivalent of two to three cans of Diet Coke daily for 13 days. Caffeine-free soft drinks were then substituted without telling the children. The children had a significant measurable decrease in attention after 24 hours, a classic symptom of caffeine withdrawal. The larger concern is that caffeine dependence in children may develop into other dependencies as the person ages.
Phosphorus -- which occurs naturally in some foods and is used as an additive in many others -- appears to weaken bones by promoting the loss of calcium. With less calcium available, the bones become more porous and prone to fracture. Animal studies demonstrate that phosphorus, a common ingredient in soft drinks as phosphoric acid, can deplete bones of calcium; there is clear and consistent bone loss with the use of cola beverages. Two human studies suggest that girls who drink more soda are more prone to broken bones by a factor of 3 to 5. Exactly how soft drinks may contribute to bone weakening is not yet known, but may be because consumption of soft drinks often displace more nutritious beverages, including milk.
The phosphoric acid in soft drinks contributes only about two percent of the phosphorus in the typical US diet, with a can of soda pop averaging about 30 milligrams. The National Academy of Sciences has set 3 grams (or 3,000 milligrams) per day as the tolerable upper limit of phosphous for children ages 1 to 8 years, and 4 grams per day for those 9 years and older. To reach that amount would require drinking at least 100 cans of soda pop per day.