Cross-sectional age- and sex-specific distributions of plasma lipids and lipoproteins are described for 1402 white children ages 6-19 yr. These children were part of a random sample examined at seven lipid research clinics (LRC) during the LRC Prevalence Study, which was established to determine the prevalence of hyperlipidemias and to describe the distribution of lipids and lipoproteins in diverse populations. These populations were not selected to be representative of the entire North American pediatric population. Nonetheless, the large numbers of children in the seven LRC populations and their socioeconomic and geographic diversity do permit analytical and comparative studies of physiological and sociodemographic variables in school-age children. This report of their lipid and lipoprotein levels is one in a series of such studies. Examination of the distribution of plasma lipids and lipoproteins showed that total cholesterol (TCH) and low-density lipoprotein cholesterol (LDL-c) were lower in males than females in most age groups studied. The difference in LDL-c is most marked in the younger age group (ages 6-9 yr) and accounts for most of the difference in TCH concentration at this age. During the adolescent period (ages 10-14 yr) a decline in high-density lipoprotein cholesterol (HDL-c) concentration occurs in the males, but not in the females. This decline continues throughout the postadolescent (ages 16-19 yr) period. The resulting difference in HDL-c mainly accounts for the higher TCH observed in the 16-19 yr-old females. Our study confirms the fall in TCH concentration at about adolescence described previously. However, it highlights the different mechanisms responsible in the two sexes. Whereas in the males the decline in TCH is mainly the result of reduction in the concentration of HDL-c, in the females it is due mainly to a gradual decline in LDL-c.
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