Researchers have found that boys' natural developmental processes put them at a greater risk for heart disease.
Scientists followed more than 500 schoolchildren in Minneapolis, Minn., from the ages of 11 to 19. Over the course of the study, readings of known risk factors for heart disease were different between boys and girls. The study found:
- Triglyceride (fat that is found in the blood) levels increased in males and decreased in females.
- High-density lipoprotein (HDL, the so-called "good" cholesterol) decreased in males and increased in females.
- Systolic blood pressure (the first number of the blood-pressure reading, which measures when the heart contracts) increased in both boys and girls, but more so in boys.
- Boys became more insulin-resistant than girls.
"By age 19, the boys were at greater cardiovascular risk," said lead author Antoinette Moran, M.D., in a statement.
"This is particularly surprising because we usually think of body fat as associated with cardiovascular risk, and the increasing risk in boys happened at the time in normal development when they were gaining muscle mass and losing fat," said Moran, professor and division chief of paediatric endocrinology and diabetes at the University of Minnesota Children's Hospital in Minneapolis.
The study was published in Circulation: Journal of the American Heart Association.
The study found no difference in cholesterol readings, or in low-density lipoprotein (LDL, so-called "bad" cholesterol) readings, between boys and girls.
At the beginning of the study, the boys and girls had similar body composition and blood pressure. During adolescence, both boys and girls gained weight. As puberty set in, body composition grew increasingly different, as boys became leaner and girls' body fat increased.
It is common knowledge that heart-disease risk factors in adults include high blood pressure, smoking, obesity, physical inactivity, abnormal cholesterol levels and insulin resistance.
The researchers concluded that more work needs to be done to investigate how the developmental processes during adolescence influence these heart-disease risk factors.
Abstract:
Changes in Insulin Resistance and Cardiovascular Risk During Adolescence. Establishment of Differential Risk in Males and Females
Steffen PhD, James S. Pankow PhD, Ching-Ping Hong MS Antoinette Moran MD, David R. Jacobs Jr PhD, Julia Steinberger MD, MS, Lyn M., and Alan R. Sinaiko MD
Background: Developmental changes in insulin resistance and cardiovascular risk were studied in youths 11 to 19 years of age.
Methods and Results: A cohort was randomly selected after blood pressure screening of Minneapolis, Minn, school children. Studies were done 3 times on this cohort and once on their siblings (996 observations on 507 individuals from 363 families). Insulin sensitivity was determined by euglycemic clamp. Body mass index and waist circumference increased similarly in both sexes from ages 11 to 19 years. Body fat decreased in males and increased in females (P<0.001). Lean body mass increased at a steeper rate in males (P<0.0001). Insulin resistance was lower in males at 11 years but increased steadily to 19 years (P=0.003); in contrast, it did not increase in females. Thus, despite being less insulin resistant at 11 years and decreasing in fatness during puberty, males became more insulin resistant than females by 19 years of age. Triglycerides increased in males and high-density lipoprotein cholesterol decreased, whereas the opposite pattern was seen in females, which resulted in higher triglycerides and lower high-density lipoprotein cholesterol in males at 19 years. No gender difference in low-density lipoprotein or total cholesterol was seen. Systolic blood pressure increased in both sexes but at a greater rate in boys (P=0.03).
Conclusions: During the transition from late childhood through adolescence, insulin resistance in males increased in association with increased triglycerides and decreased high-density lipoprotein cholesterol, despite a concurrent reduction in body fatness, whereas the opposite occurred in females. These gender-related developmental changes in insulin resistance, which were independent from changes in fatness, total cholesterol, and low-density lipoprotein cholesterol, are consistent with an early role for insulin resistance in the increased cardiovascular risk found in males.
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