August 2007 — Exercise cannot reduce a
sodium-retaining hormone in African Americans which is known to
potentially cause hypertension, found Michael D. Brown, Ph.D., the
senior author of a study in the September issue of Experimental
Physiology. Brown is an associate professor of kinesiology at Temple
University’s College of Health Professions.
The hormone, aldosterone, influences the kidney’s regulation of
blood pressure, but too much of it can contribute to the development of
hypertension because it causes the kidney to retain salt. Aldosterone,
released by the adrenal glands on top of the kidneys, plays a role in
the complex system used by the body to regulate blood pressure.
"Although the results are discouraging for African Americans and
hypertension, it’ll point us in other directions that may have more
potential and could be the key to reducing hypertension," said Brown,
who has a background in exercise physiology.
Many African Americans develop the salt-sensitive form of
hypertension. Approximately 40 percent of African Americans have
hypertension — the highest rate of any racial or ethnic group in the
United States — but there is little data about what makes them more
susceptible to this condition, Brown said.
This study is based on the premise that the prevalence of blood
pressure sensitivity to salt is extremely high is African Americans.
Alterations in aldosterone regulation may play a role because
aldosterone causes the kidney to retain salt. Brown said he wanted to
find out if exercise could lower the levels.
In the study, he found that the level of aldosterone was related to
how the two racial groups distributed body fat. Caucasians generally
stored fat in the abdomen area, whereas African Americans had fat
distributed throughout the body in a layer under the skin. The
six-month study involving 35 Caucasians and African Americans with
hypertension found that aerobic exercise training program reduced
aldosterone levels in Caucasians by 32 percent, but levels for African
Americans were reduced by only 8 percent. Total body fat was reduced
only in Caucasians, which might be a clue to the drop in aldosterone.
"The kidneys help to regulate blood pressure by changing the levels
of salt and water in our body. Sometimes the kidneys reset at a higher
blood pressure level if it has retained too much salt," Brown said.
While the study showed exercise did not lower aldosterone in African
Americans, exercise still has many other benefits for this population,
"Exercise has the capacity to affect so many things. It’s a way for the body to correct itself," he added.
Brown will continue his research in this area with a $3.5 million
National Institutes of Health grant awarded earlier this year. In
September, Brown will recruit African Americans with hypertension for a
study on how exercise can improve the blood vessel condition. The study
will also take an in-depth look at how genes can contribute to
"Solving the cause of hypertension is similar to solving a big
puzzle. Each piece of the puzzle represents a contributing factor to
hypertension. Each of these pieces, or possible causes of hypertension,
needs to be studied in a systematic way," Brown said.
Source : Temple University