The proportion of young people ages 6 to 19 with high total cholesterol dropped 28 percent between the two time periods sampled in the report, from 11.3 percent in 1988-94 down to 8.1 percent in 2007-10, the new study found.
At the same time, the average American teen's levels of "good" HDL cholesterol, "bad" LDL cholesterol and triglycerides -- dangerous fats that circulate in the bloodstream and slowly clog arteries -- improved too.
Scientists said they weren't sure what had led to the encouraging changes reported Tuesday in the Journal of the American Medical Association. Use of cholesterol-lowering drugs remains rare among children, they noted. Their best guess is that some environmental factor - perhaps lifestyle changes - may be driving down cholesterol, and several surmised that the improvements were rooted in reduced rates of smoking and the success of campaigns to lower fat and cholesterol in the diet.
The findings "cannot be interpreted as anything but good news," said Dr. Rae-Ellen Kavey, a specialist in children and cholesterol at the University of Rochester in New York. Kavey acknowledged that she found some of the changes inexplicable, but said she did not question their significance, since improvements were seen in kids of all ages, ethnic backgrounds and even among children who were already obese.
Study lead author Dr. Brian K. Kit, a researcher with the Centers for Disease Control and Prevention's National Center for Health Statistics, said that the apparent good news was qualified by the finding that 1 in 10 American children still has cholesterol readings that raise his or her risk for developing heart disease.
Still, the findings may temper a tide of gloom over the prognosis for the nation's youths, whose obesity rate has tripled over the last three decades. A recent projection by the American Heart Association estimated that the increase would translate into a 16.6 percent rise in heart attacks by 2030.
The trends found in the latest study "may portend improved . outcomes for the future," wrote Dr. Sarah D. de Ferranti, a specialist in heart disease prevention at Boston Children's Hospital, in an editorial accompanying the article.
Given the high rates of obesity and diabetes among children and their well-chronicled sedentary behavior, it is unlikely that children are adopting heart-healthy habits, de Ferranti added. More plausibly, she said, what has improved is the nutritional profile of foods that children are offered at school and home or that they can easily buy for themselves.
During the decades studied, a growing awareness of the dangers of a diet high in saturated fat led many parents to switch from whole milk to reduced-fat or fat-free milk, and food manufacturers reformulated many products to reduce their saturated fat content.
And starting in 2003, a public health campaign ultimately led to the removal of most trans-fatty acids - which raise heart risk even more than saturated fats - from packaged foods sold in the United States. From 2000 to 2009, the level of trans-fatty acids in the average middle-aged American's bloodstream had plummeted 58 percent, according to a February report in the Journal of the American Medical Association.
But de Ferranti cautioned that the changes in foods on the American market could have a dark side: In reducing saturated fat and removing trans fats, many manufacturers have pumped up the sugar and carbohydrate content. That may help explain why obesity among children and adults continued to grow through much of the study period, even as cholesterol readings improved.
Though complex, cholesterol measures have become one of medicine's strongest predictors of a person's risk of cardiovascular disease. Researchers have long linked obesity to rising levels of dangerous cholesterol and an increased likelihood of heart attacks and strokes.
The study underscores that cholesterol is "not completely driven by obesity," said Dr. Stephen R. Daniels, pediatrics chief at Children's Hospital Colorado. As researchers unravel which other factors most influence cholesterol profiles, children across all weight classes can learn how to protect themselves from developing cardiovascular disease, Daniels said.
©2012 Los Angeles Times
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