More Muscle Means Better Regulation of Blood Pressure, Study Finds

[Guest guest]

More Muscle Means Better Regulation of Blood Pressure, Study Finds

24 Nov 2004 http://www.medicalnewstoday.com/medicalnews.php?newsid=16819

People with more muscle than fat have increased ability to regulate

their blood pressure in response to stress, according to a Medical

College of Georgia study.

“Fitness facilitates the ability to regulate blood pressure; fatness

impedes your ability to regulate blood pressure through your ability to

regulate sodium,” says Dr. Harshfield, hypertension researcher

and second author on the study in the November issue of the American

Journal of Hypertension.

“When you are under stress, your blood pressure should go up and when

the stress is over, it should come back down,” says Martha ,

research manager and the study's lead author. “Look at the Olympic

athletes. Certainly their pressures are up when they are swimming or

running or doing gymnastics, but I'm sure their pressures come back down

relatively quickly afterward.”

Previous studies have made the seemingly odd link between lean body mass

and higher blood pressure in adults and children. And when the MCG

researchers started analyzing their data on how 127 young adults with

normal blood pressure responded to stress, they found the same thing. “I

thought the data was wrong,” says Dr. Harshfield.

What might be wrong is the notion that an increase in blood pressure is

bad. “If you think about it, that concept doesn't make sense,” Dr.

Harshfield says. “If you are in a stressful situation, your blood

pressure should go up. If it doesn't, then you do have a problem,” he

says, referencing the natural fight-or-flight mechanism that enables

more blood and oxygen to get to the body during stress.

When the researchers looked at the percentages of fat and lean tissue on

their study participants and looked at their ability to excrete sodium -

the primary mechanism for dropping blood pressure back to normal - they

found those with more fat had a decreased ability to excrete sodium.

MCG researchers say lean body mass may have gotten a bad rap because

previous studies looked at casual blood pressure and did not factor in

fat's contribution. Not unlike building muscle in response to lifting

heavier weights, the body also builds more lean tissue to support more

fat. “The argument was that you have to have greater lean mass to carry

the greater fat mass, so it was really the greater fat mass that was the

culprit,” Dr. Harshfield says. “I am sure this is true, particularly in

adults.”

Fat, especially abdominal fat, secretes angiotensin which makes

angiotensin II, a powerful vasoconstrictor that also directs the kidneys

to absorb more sodium so blood vessels retain more fluid volume, says

Dr. Harshfield, who is principal investigator on a separate National

Institutes of Health grant looking at how fat contributes to high blood

pressure. Research he published in 2003 in Hypertension also shows that

overweight boys have greater blood pressure increase in response to

stress than their female peers and decreased ability to return to

normal.

For the newly published study, researchers measured the blood pressure

of study participants every 15 minutes throughout a two-hour baseline

period, an hour of competitive video games and a two-hour recovery

period.

They found that while blood pressure increased an appropriate average of

5 percent in response to the stress of video games, participants who had

more lean muscle mass than fat were better able to return to normal

levels through this sodium excretion process called natriuresis.

Previous studies by Dr. Harshfield have shown that race also contributes

to elevated pressures following stress because of blacks' reduced

ability to excrete sodium. The new study shows that high body fat is

another independent predictor of the abnormal response.

“The major finding of this study is that body composition is related to

the pressure natriuresis response to mental stress,” the researchers

write. “Specifically, (lean body mass) was associated with higher (blood

pressure) during stress. In contrast, greater body fat was associated

with a slower natriuretic response to stress as well as slower

natriuresis during stress, which is in part related to (angiotensis

II).”

Those findings point back to the adage that fitness is good and should

start early in life, Mrs. says.

The research was funded by grants from the NIH.