Teenage boys are at a greater risk of developing heart disease than girls because of certain natural changes during their development, researchers at the University of Minnesota Children's Hospital in Minneapolis, have found.
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.
"Women's protective advantage against heart disease starts young," said Antoinette Moran, M.D., lead author of the study and professor and division chief of pediatric endocrinology and diabetes at the University of Minnesota Children's Hospital in Minneapolis.
In adults, a constellation of factors increases the risk of heart disease. They include high blood pressure, smoking, obesity, physical inactivity, abnormal cholesterol levels and insulin resistance (a pre-diabetic condition in which the body can't use insulin effectively).
Researchers found no gender difference in two other cardiovascular risk factors, total cholesterol and low-density lipoprotein (LDL or "bad") cholesterol.
"By age 19, the boys were at greater cardiovascular risk. 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," Moran said.
Although girls gained cardiovascular protection when their proportion of body fat was increasing, excess fat is still a cause for concern.
"Obesity trumps all of the other factors and erases any gender-protective effect. Obese boys and girls and men and women all have higher cardiovascular risk," Moran said.
The researchers said further studies are needed to better understand the development of cardiovascular protection during adolescence.
"That the protection associated with female gender starts young is fascinating and something that we don't understand very well. That this protection emerges during puberty and disappears after menopause suggests that sex hormones give women a protective advantage. There's still a lot that needs to be sorted out in future studies - estrogen may be protective or testosterone may be harmful," Moran said.
Moran noted that this is normal physiology and not something that is influenced by lifestyle factors.
The study is published in Circulation: Journal of the American Heart Association.