image: Dr. Gregory Harshfield, director of the Medical College of Georgia's Georgia Prevention Institute, and Martha Castles, research manager. view more
Credit: Medical College of Georgia
Using a model that mimics common life stressors, researchers found estrogen levels drop during stress in healthy black girls but remain consistent in whites, said Dr. Gregory Harshfield, director of the Medical College of Georgia's Georgia Prevention Institute.
"Estrogen, which helps blood vessels dilate, is good for your blood vessels and if you lose that protection during periods of stress in the day it may contribute to the early development of heart disease we typically see in black women," says Dr. Harshfield.
Research being presented during the 21st Annual International Interdisciplinary Conference on Hypertension and Related Cardiovascular Risk Factors in Ethnic Populations in Atlanta June 23-26 looked at 48 mostly female teens with normal blood pressure.
Researchers found the greatest changes in blood pressure response to stress in black girls and blood samples taken before, during and one hour after playing a competitive video game showed their estrogen levels dropped during stress and went back up afterward.
"Conventional thinking tells us estrogen is not normally a major player in regulating blood pressure during stress," says Dr. Harshfield. "This tells us sex hormones do play a role in regulating blood pressure but, unfortunately, it's a bad one in black females."
Estrogen influences blood pressure by releasing nitric oxide, a vasodilator, and by blunting the response of the sympathetic nervous system – the fight or flight response – as well as angiotensin II, a vasodilator. Estrogen is believed to be one of the main reasons women have lower rates of heart disease than men until after menopause, says Martha Castles, research manager, who is presenting the research.
"We are now thinking that when black girls are under stress, they are losing all the protective effects of estrogen," Dr. Harshfield says. "In whites under stress, their estrogen levels are consistent so they are secreting vasodilators, they are blocking angiotensin and the sympathetic nervous system so the stress is not affecting them as much." In fact, black girls in the study also showed the greatest change in angiotensin levels in response to stress.
The prevalence of hypertension is increasing in females, he says, particularly in black females whose prevalence is greater than black males and overall death rate from hypertension is more than twice that of white females.
Dr. Harshfield notes that little is known about mechanisms underlying racial differences in blood pressure. His previous work has shown that, compared to their white peers, healthy black girls and boys also have reduced ability to secrete sodium following stress, which leaves their blood pressure elevated for longer periods and may help explain why blood pressures don't decrease as much during sleep. "Estrogen is probably another mechanism through which the blood pressure is staying elevated," he says.
The work was funded by the National Institutes of Health.