Against the drumbeat of bad news on obesity and diabetes among children, researchers have uncovered a cause for cautious optimism: a steady and significant improvement in the cholesterol profiles of American kids over the past 20 years.

The proportion of young people ages 6 to 19 with high total cholesterol dropped 28% between the two time periods sampled in the report, from 11.3% in 1988-94 down to 8.1% 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 Assn. 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.

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