This decline is similar to the somewhat larger decrease in cholesterol levels among adults during the same time period. The overall downward trend in cholesterol levels accompanies a simultaneous decline in saturated fat and cholesterol intake among both adolescents and adults in the U.S.
"This impressive drop in cholesterol levels among U.S. adolescents gives us hope for their future heart-health. Today's children with high cholesterol tend to be tomorrow's adults with raised levels, and the higher the cholesterol, the greater the risk of atherosclerosis and heart disease," said Dr. Claude Lenfant, Director of the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health.
The new analysis is based on data from the third National Health and Nutrition Examination Survey (NHANES) conducted by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention, between 1988 and 1994. Trend information was based on NHANES III and earlier versions of the survey.
In the period 1966-1970, the average total cholesterol level in adolescents was 167 mg/dL. By 1988-1994, the level had dropped to 160 mg/dL. The average total cholesterol level in adults declined by 10 mg/dL (from 213 to 203 mg/dL) from 1976-1980 to 1988-1994, and by 17 mg/dL (from 220 to 203 mg/dL) from 1960-1962 to1988-1994. The reason for the greater drop in adults is unclear, according to the authors of the study, but may be partially due to the fact that adolescents start at lower total cholesterol levels and experience changes in HDL (good) cholesterol and other lipids in conjunction with puberty.
At the same time as the decline in cholesterol levels, adolescents were improving their diet. Average saturated fat consumption of 12-to-17 year olds declined from 14 percent of calories in 1971- 1974 to 12 percent of calories in 1988-1994. During the same years, total fat intake dropped from 37 to 34 percent of calories and daily cholesterol intake fell from 350 mg to 265 mg.
Adults have also reduced their consumption of saturated fat, total fat, and cholesterol. This improvement in diet -- and the resulting drop in cholesterol levels -- have been important contributors to the decline in deaths from heart disease. Since 1972, deaths from coronary heart disease have fallen by nearly 53 percent.
"The prevention of heart disease begins in childhood – so the importance of dietary changes in young people is clear," said Dr. James Cleeman, coordinator of the National Cholesterol Education program (NCEP), which is administered by the NHLBI. "If these children can maintain lower cholesterol levels into adulthood, they will postpone or prevent the onset of coronary disease -- an important health achievement," he said.
However, Dr. Cleeman, who is a coauthor of the latest study, noted that more progress is needed. "Only one in six children and adolescents are fully meeting dietary recommendations for fat and cholesterol," he added.
The NCEP's recommendations call for all healthy Americans over age 2 to limit saturated fat intake to less than 10 percent of calories, total fat intake to 30 percent of total calories or less, and cholesterol to less than 300 mg per day.
"Today's youth also need to be more physically active–only about half of today's adolescents are getting enough exercise," said Dr. Cleeman. "This ties into the increase in overweight among children and adolescents in the U.S. -- and the need for better weight control," he said.
Dr. Edward J. Sondik, Director of the National Center for Health Statistics, said, "It is essential to have this array of data to track positive change, identify remaining problems, and better understand the complex relationship between diet, exercise and health." For example, he noted, "the next NHANES survey–to start soon–will continue to report on dietary behaviors and health measures but will also tell us how much time kids spend before the TV and on the computer and will include new tests of cardiovascular fitness."
Although the new analysis found that total cholesterol levels decreased in all race/sex groups studied, black adolescents experienced a smaller decline compared to whites – 8 mg/dL in white adolescents and 5 mg/dL in black adolescents. In general, total cholesterol levels were about 5 to 7 mg/dL higher in non-Hispanic black adolescents compared to non-Hispanic whites and Mexican Americans. Of all the groups, black females continued to have the highest total cholesterol (168 mg/dL) and experienced the smallest decrease over time – 4 mg/dL. The finding of higher total cholesterol levels in black adolescents differs from the pattern in adults, in whom blacks have lower total cholesterol than whites.
The authors did not speculate about the racial differences in adolescents, but they noted the higher prevalence of overweight among non-Hispanic black adolescents compared with non-Hispanic white and Mexican-American children and adolescents.
For more information on cholesterol, visit the NHLBI's website at http://www.nhlbi.nih.gov.