DALLAS, June 17 -- A new study on growth patterns in children and teenagers confirms striking fluctuations in blood cholesterol levels, suggesting that normal cutpoints for testing may need to be re-examined, says Darwin Labarthe, M.D., Ph.D., the report's lead author.
"There was evidence that cholesterol levels fluctuated, but it was not emphasized before and our study suggests that we may need to re-examine the National Cholesterol Education Program (NCEP) pediatric panel guidelines," says Labarthe.
The researcher's report appears in today's American Heart Association journal Circulation. "Project HeartBeat!" is a study of 678 young people ages 8 to 18 in suburban Houston. The project is providing the closest look yet at how blood cholesterol levels, blood pressures and other factors that may adversely influence heart health later in life change as children and teenagers mature, say University of Texas Houston Health Science Center (UTHHSC) investigators.
Another major finding is that boys' body fatness levels tend to swoop downward, roughly parallel to the drop in their cholesterol levels, as they mature. In the girls, body weight increases during puberty, but the percentage of body fat changes very little across the whole age range from 8 to 18 -- even as their average cholesterol levels are dropping in roughly similar fashion to those of boys. In boys, body weight also increases, but the weight gain is due to mainly muscle, not an increase in fat tissue.
"This raises some fascinating questions about our belief that the key to preventing high cholesterol is to modify diet and physical activity for the purpose of limiting body fatness as the necessary link," Labarthe says. "Body fatness isn't the culprit, apparently, at least for girls.
"So this suggests a new insight into ways to think about preventive strategies at least during this age period," he continues. The researchers will further analyze a wide variety of data that includes dietary information, sex hormone and physical activity levels, "to see, at least for girls, if fat isn't the explanation for the change in cholesterol, what is?" he says.
"These observations suggest that the percent of body weight that is fat is not closely related to the change in cholesterol for girls, in this age range," Labarthe says. But that is not to suggest, he cautions, that Americans should stop striving for proper balance in diet and physical activity to avoid excess weight gain.
In future reports, the researchers expect to detail individual variations in each of the major cardiovascular risk factors taking into account age, sex, ethnicity, sexual maturation and other components.
NCEP is a joint effort by the National Heart, Lung and Blood Institute and over 30 other health organizations to promote cholesterol screening and to develop guidelines for physicians in their testing of their patients' blood cholesterol levels. The American Heart Association, one of the 30 participating groups, recommends that physicians continue to use the current guidelines until this and other new research can be evaluated.
Richard Deckelbaum, M.D., member of the NCEP and AHA's Nutrition Committee, says that the NCEP panel selected screening guidelines that best apply to the entire pediatric population. "This research confirms what NCEP's pediatric panel has described in the 'ups and downs' in cholesterol levels among youths and shows gender differences in the relationship between cholesterol levels and body fat. This may provide an opportunity for us to review our recommendations. While this occurs, we recommend that the current guidelines on cholesterol screening be followed.
"While these studies are of high interest, it is important to realize that the NCEP children's guidelines were formulated from information gathered from multiple geographic locations across the United States. More data from other sites and studies would still be needed before implementing new cholesterol guidelines nationwide."
He also points out that the curve and drop in cholesterol levels in adolescence has been well known in both boys and girls for over 15 years. Also contributions to this drop have been recognized to be different between the sexes. "Knowing this the pediatric NCEP panel suggested screening guidelines that apply best to the entire pediatric population, and which would not wrongly over identify children at risk," says Deckelbaum.
Futhermore, the NCEP recognized that for most children, obesity is not the major culprit in elevating cholesterol level, although obesity does contribute in some children.
In the study approximately equal numbers of boys and girls were 8 to 14 years old when they enrolled. Charting the children's cholesterol levels three times each year during the four-year study gave researchers a dramatically different view of changes that occur during years of fast growth and maturation, according to Labarthe.
"By doing the examinations every four months, we were able to show far greater variability in individual cholesterol levels than has been known from previous studies," says Labarthe, who is James W. Rockwell Professor of Public Health at UTHHSC. Most conclusions from those earlier studies, he notes, were based on readings one or more years apart.
So what does it mean if individual cholesterol levels swing rather wildly up and down, while average levels generally trend downward as normal children pass through puberty?
"An important implication is that screening based on a single cholesterol measure is probably less reliable than has previously been thought," Labarthe declares.
NCEP guidelines are based on a cutoff point at which youths with cholesterol levels in the top 25 percent -- above 170 milligrams per deciliter (mg/dl) of blood -- are considered to be abnormally high. In those cases, a repeat measure is needed. If levels are still high, then more tests are needed to measure other blood components.
Similarly, Labarthe says his team's findings suggest that a child with an initially high reading could safely be re-measured for total cholesterol alone before going on to the more costly testing. And the 170 mg/dl flashpoint itself, the researcher says, is based on "old survey data" whose straight-across reference values don't take into account fluctuations in cholesterol at various ages.
"It's obvious that if there is a curving pattern of change in cholesterol with age, a straight line that represents a fixed criterion of 170 milligrams per deciliter for all ages is going to mis-classify a large proportion of children," Labarthe says. Depending on age and sex -- the cholesterol curves for the two sexes don't exactly match. Some children will be either over-diagnosed or under-diagnosed, he says.
From their analysis, the researchers say they can now pinpoint an appropriate cholesterol level at each age, and separately for girls and boys. "A boy age 10 would be considered to have high cholesterol at a certain value, while a boy of 16 would be thought to have high cholesterol at a much lower level," Labarthe says. Blood pressure screening recommendations for children, he notes, already reflect similar patterns of change that have been observed based on age.
Labarthe's co-authors are: Milton Z. Nichaman, M.D.; Sc.D.; Ronald B. Harrist, Ph.D.; Jo Anne Grunbaum, Ed.D.; and Shifan Dai, M.D., for the Project Heartbeat! investigators.
Circulation is one of five journals published in Dallas by the American Heart Association. ### Media advisory: Dr. Labarthe can be reached in Houston by calling (713) 500-9416. Dr. Deckelbaum can be reached in New York by calling (212) 305-4808. Reporters may call (214) 706-1173 for copies of the AHA journal report. (Please do not publish telephone numbers.)