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September 26, 2011
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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.
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FILE - In this Dec. 28, 2001 file photo, John Matheny sits during one of his three weekly sessions at the Morgantown Dialysis Center where he receives his kidney dialysis treatments, near Granville, W. Va. A major study to be published on Thursday, Sept. 22, 2011 challenges the way diabetics and others with failing kidneys have been treated for half a century, finding that three-times-a-week dialysis to cleanse the blood of toxins may not be enough. Deaths, heart attacks and hospitalizations were much higher on the day after the two-day interval between treatments each week than at other times, the federally funded study found. (AP Photo/Dale Sparks, File)
LOS ANGELES (AP) — A major study challenges the way diabetics and others with failing kidneys have been treated for half a century, finding that three-times-a-week dialysis to cleanse the blood of toxins may not be enough.Deaths, heart attacks and hospitalizations were much higher on the day after the two-day interval between treatments each week than at other times, the federally funded study found.The president of the National Kidney Foundation said she was "very troubled" by the results published in Thursday's New England Journal of Medicine."We could be doing a better job for our dialysis patients" and that might mean doing it more often, said Dr. Lynda Szczech, a Duke University kidney specialist who had no role in the study.Kidneys rid the body of waste and fluids. Most of the 400,000 Americans with failing kidneys stay alive by getting their blood purified by a machine three days a week at dialysis clinics — usually on Mondays, Wednesdays and Fridays or on Tuesdays, Thursdays and Saturdays. In both cases, there's a two-day break between the last session of the week and the next one.The three-day dialysis schedule has been around since the mid-1960s and gives patients a weekend break from the grueling hours of being hooked up to a machine.However, doctors have suspected that the two-day hiatus between treatments was risky, and smaller studies have found more heart-related deaths on the day after the gap."All the fluids and toxins are built up to the highest extent on Monday morning right before dialysis," said Dr. Anthony Bleyer of Wake Forest Baptist Medical Center in North Carolina, who has done similar studies.The latest research, funded by the National Institutes of Health, is the largest yet. It was done by Dr. Robert Foley of the University of Minnesota and colleagues. All reported receiving fees from dialysis clinics and suppliers.The team analyzed medical records of 32,000 people who had in-center dialysis three times a week from 2005 through 2008. The average age was 62 and a quarter had been on dialysis for a year or less. After about two years of follow-up, 41 percent had died, including 17 percent from heart-related causes.Monday was the riskiest day for people on a Monday-Wednesday-Friday schedule. For those on a Tuesday-Thursday-Saturday schedule, the riskiest day was Tuesday.Researchers found a 22 percent higher risk of death on the day after a long break compared with other days of the week. Put another way: For every 100 people on dialysis for a year, 22 would die on the day after the long interval versus 18 on other days.Hospital admissions for stroke and heart-related problems more than doubled on the day after a long break than on other days — 44 versus 20 for every 100 people treated.Fixing this problem, however, could be daunting for patients, busy dialysis centers and insurers and it would require a rethinking of how dialysis is currently delivered.Medicare covers the cost of dialysis, regardless of age, spending about $77,000 annually per person. It covers thrice-weekly treatment, but people can get a fourth session if needed.Dr. Paul Eggers of the National Institute of Diabetes and Digestive and Kidney Diseases said adjusting how dialysis is done "would require some fairly convincing evidence. I'm not sure this one study would be sufficient to change" standard practice.Kidney expert Dr. Eli Friedman of SUNY Downstate Medical Center in New York, said he's in favor of every-other-day dialysis or even daily dialysis. But it would mean "a multibillion dollar change," said Friedman, who launched the country's first federally funded dialysis center.A clinic operator said increasing treatments would require additional staff. And patients also would have to be willing to come in more often."They don't even like coming in three times a week. It's completely understandable. It's not fun," said Dr. Allen Nissenson, chief medical officer at DaVita, which runs more than 1,600 clinics around the country.There has been recent interest in more frequent dialysis after studies hinted that it made people feel healthier.This year, Medicare started giving clinics a financial incentive to teach patients to do dialysis at home, allowing them to cleanse their blood more often. But this option is not for everyone. It requires intense training and patients need a helper at home.Unless rules change, Wake Forest's Bleyer said people can take simple steps to reduce their risk by not drinking too much fluid between long dialysis breaks and eating a healthy diet."Patients must be a little more careful on the weekend than on other days of the week," he said.Carol Thomas, who has been on dialysis since 2007, watches her water intake especially on weekends and avoids dairy, beans and nuts, which are high in certain nutrients that can cause complications.Thomas, of Sacramento, Calif., said home dialysis is not an option because she doesn't have someone to help her. Would she make the trip for dialysis more often if given the choice?"It's an inconvenience, but probably if it meant lengthening my life," the 69-year-old said.___Online:New England Journal: http://www.nejm.orgKidney disease information: http://kidney.niddk.nih.govNational Kidney Foundation: http://www.kidney.orgAmerican Association of Kidney Patients: http://www.aakp.org___Alicia Chang can be followed at: http://twitter.com/SciWriAliciaAssociated Press 
