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DAVID GREENE, Host:

It's MORNING EDITION, from NPR News. Good morning. I'm David Greene, sitting in for Renee Montagne.

STEVE INSKEEP, Host:

And I'm Steve Inskeep.

Today in Your Health, we'll ask about the best way to relieve pain, although first, we look at why children have a love affair with sugar and how it can help lessen their pain. Gretchen Cuda-Kroen reports.

GRETCHEN CUDA: Ask a child if they like sweets, and the conversation is bound to go something like this...

What kinds of sweet things do you like?

KEELY MCGINTY: Toast with sugar on it, ice cream, cookies.

CUDA: Would you, for example, ever put sugar on your Frosted Flakes, or anything like that? Would you put more sugar on it?

MCGINTY: Yes.

CUDA: Most kids, like eight-year-old Keely McGinty, love sugar. And according to researcher Julie Menella of the Monell Chemical Senses Center, that sweet-tooth is biologically hard-wired into us from birth.

JULIE MENELLA: We know that the baby - the newborn can detect sweet and will actually prefer sweeter solutions to less sweet ones. So, the basic biology of the child, they don't have to learn to like sweet or salt. It's there from before birth.

CUDA: Unlike adults who often find overly sugary things unpleasant, Menella says kids simply taste things differently.

MENELLA: They actually are living in different sensory worlds when it comes to these 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.

CUDA: A preference for sweet, caloric substances during rapid growth may have given children an evolutionary advantage when calories were scarce. The fact is that sugar just doesn't taste good to children, it actually makes them feel good, too. Menella's research has shown that sugar is a natural pain reliever in babies, 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.

MENELLA: So it's much more powerful than we can imagine when it comes to sweets in children.

CUDA: In order to better understand the power of sugar, Menella and others actually measured this preference for sweet tastes in the laboratory. They gave adults and children of all ages water mixed with various amounts of sugar, and asked them which ones they preferred. And while adults prefer sugar concentrations similar to that of a can of soda, children prefer at least twice that concentration. And when it comes to younger children, the more the better.

Is there anything that's too sweet for you, that you say, oh, that's just too much sugar?

UNIDENTIFIED CHILD: No.

CUDA: Never?

CHILD: Mm-hmm.

SUE COLDWELL: You really can't find a point at which the sugar solutions are too sweet. You can keep putting sugar in to the point where you can't dissolve it in the water anymore, and they still like it.

CUDA: That's Sue Coldwell, a researcher at the University of Washington who's studies sweet preferences in children. She says that a child's tastes change about age 15 or 16 when children go through puberty.

She was curious why that was, so she and her colleagues gave the same 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, and those whose growth had already stopped had taste preferences similar to adults.

COLDWELL: So we found support for that old notion that our grandmothers had that when you're growing rapidly, your preference for these highly sweet, caloric substances increases, and then as your growth slows down, the preference drops.

CUDA: 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 appetite, and even directly bind to the tongue where they affect the preference for sweet tastes. And Coldwell suspects that the hormones from growing bones may be doing the same thing.

COLDWELL: I don't know for sure, but I'm 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.

CUDA: 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. And if the goal is to get children to reduce their intake of sugar, understanding the biology behind their cravings is a first step.

For NPR news, I'm Gretchen Cuda-Kroen, in Cleveland.

INSKEEP: And for more on sugar's effects, check out NPR's new food blog, which is ironically called The Salt. It's at npr.org.

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