Ask a child if they like sweets and the answer is almost universally a resounding "Yes!" It's no surprise to most parents that kids love candy, cookies, sweetened drinks, and some kids have even been known to add sugar to a bowl of Frosted Flakes. But don't blame the kids, say researchers, it's biology.
Scientific evidence shows that children not only have a stronger preference for sugar than adults – but that sweet-tooth is hardwired from Day One.
"We know that the newborn can detect sweet and will actually prefer sweeter solutions to less sweet ones. The basic biology of the child is that they don't have to learn to like sweet or salt. It's there from before birth," explains Julie Mennella of the Monell Chemical Senses Center.
Unlike adults, who often find overly sugary things unpleasant, Mennella says kids are actually living in different sensory worlds than adults when it comes to basic tastes.
"They prefer much more intense sweetness and saltiness than the adult and it doesn't decrease until late adolescence, and we have some evidence they may be more sensitive to bitter taste," Mennella says.
A reason for this may be that a preference for sweet, caloric substances during rapid growth may have given children as an evolutionary advantage when calories were scarce. That notion is supported by the fact that sugar doesn't just taste good to children -– it actually makes them feel good too.
Mennella's research has shown that sugar is a natural pain reliever in children, and many hospitals even put a sweet tasting liquid in a baby's mouth during circumcisions or heel stick procedures to help lessen the pain.
When researchers gave adults and children water mixed with various amounts of sugar, adults preferred sugar concentrations similar to that of a can of soda, while finding higher concentrations too sweet. By comparison, children preferred at least twice that concentration, and younger children had virtually no limit.
"You can keep putting sugar in to the point where you can't dissolve it in the water anymore and they still like it," says Sue Coldwell, a researcher at the University of Washington who has studied kids and sweets.
But there seems to be an age limit on the super-sized sugar preference.
Coldwell and her colleagues suspected that sugar preferences changed during adolescence. They checked a bunch of indicators, like body image and hormones, and then they checked bone growth. They gave the sugar-water test to adolescents while simultaneously measuring a marker of bone growth in their urine. What they found was that kids who were still growing preferred sweets. While those whose growth had already stopped –- around age 15 or 16 — had taste preferences similar to adults.
Exactly how this all works is still somewhat of a mystery, but Coldwell says that one important clue lies in the discovery that growing bones actually secrete hormones that can influence metabolism. Other well-known metabolic hormones like leptin and insulin have been shown to act on brain areas that control cravings and appetites, and even directly bind to the tongue where they affect the preference for sweet tastes. Coldwell suspects that hormones from growing bones may be doing the same thing. In other words, it's not your kid's fault he raided the cookie jar – the hormones from his growing bones made him do it.
"I don't know for sure but I am very suspicious that the bones are somehow telling either the brain or the tongue that there is energy needed for their growth and signaling for that preference to increase," says Coldwell.
That's not to say a kid can't overdo it. In a modern world of calorie overload and childhood obesity, cravings for sugar are no longer the evolutionary advantage they once might have once been. But if the goal is to get children to reduce their intake of sugar, researchers say understanding the biology behind their cravings is the first step.