...From the pages of Agricultural Research magazine
Selenium's Secrets Probed in New Study
Chemist Chris Hawkes prepares
a hair specimen from a
volunteer to analyze its
selenium content. Hair can
provide a history of dietary
selenium intakes from a couple
of weeks to many months in
Tomorrow's breads, pastas, and other flour-based foods might be specially
enriched with seleniuman essential nutrient. But more research
into the activity of selenium in our bodies needs to be done before
the United States embarks on fortifying foods with this trace element.
That's why ARS research chemist
Chris Hawkes is leading an innovative investigation of moderately high
doses of selenium. He is looking at the effects on human cardiovascular
health, immune function, and reproductive health. Hawkes is at the ARS
Western Human Nutrition Research Center at Davis, California.
The selenium experiment, now in its second phase, will provide new,
detailed information about this mineral. More than 30 healthy men aged
18 to 45 are participating as volunteers in this study.
As part of a study on selenium's
At regular intervals, the men will visit the center to provide samples
of blood, urine, semen, and other specimens for laboratory tests. They
will also receive tests of cardiovascular function and several other
health indicators. In addition, they will turn in detailed records of
their exercise, general health, and the foods they have eaten during
specific 3-day periods.
"This multiphase, multiple-variable experiment will give us a
more detailed look at selenium's activities over a longer period than
the first phase of our study," says Hawkes. The first phase included
11 volunteers who lived at the center for 120 days and ate meals specially
prepared for them. In the current phase of the study, volunteers live
at home with a free choice of what to eat. They come to the center only
Seafoodand grains and meats from regions with selenium-rich soilsare
good sources of this mineral. Other sources include dairy products and
Scientists have known for years that selenium is needed for proper
growth and reproduction in animals. This work with animals has also
indicated that selenium is critical to keeping the thyroid active and
functioning properly. Too, it is a powerful antioxidant that protects
cells from oxidation byproducts known as peroxides. But selenium still
For example, Hawkes says, recent studies, done elsewhere with laboratory
animals raised on selenium-deficient feed, have suggested that selenium
helps fight cardiovascular disease. Arteries in those animals did not
properly expand and contract. Arteries are the stretchy vessels that
carry oxygenated blood away from the heart, out to the rest of the body.
That expansion and contraction, or vascular responsiveness, is vital
for maintaining a healthful flow of blood. "In our study, we are
measuring the changes in vascular responsiveness of these volunteers
by regularly monitoring the diameter and flow rate of the brachial artery
in the upper arm," says Hawkes. "This is a standard test of
"We use an inflated blood pressure cuff on the forearm to temporarily
block the flow of blood. Then we release the cuff and use an ultrasound
device to see and measure the response of the artery. In a person with
good vascular tone, the artery will quickly expand once the cuff is
removed. We think a selenium-containing enzyme may be involved in signaling
the artery to expand."
For these cardiovascular tests, Hawkes is collaborating with Lawrence
Laslett, M.D., a cardiologist at the University of California at Davis
School of Medicine.
Says Hawkes, "Selenium is already being tested by medical professionals
to fight AIDS. But the exact interaction between selenium and the immune
system in healthy peoplesuch as those in our studyisn't
In phase one of Hawkes's study, he found that selenium increased the
antibody response to vaccinations and improved the growth of lymphocytes,
a type of white blood cell. Hawkes did that work with research chemist
Darshan S. Kelley of the Western Human Nutrition Research Center.
In this newest phase of the study, Hawkes is monitoring a comprehensive
panel of indicators of immune function in the blood to track selenium's
effects. He is also collecting data from skin sensitivity tests for
a variety of allergens and is asking volunteers to keep a personal "sniffle
diary" to document colds and other respiratory infections.
He is analyzing the volunteers' reproductive health because the first
phase of the study indicated that a high-selenium regimen might lower
sperm motilitythat is, the ability of sperm to move or swim.
"We want to see if the same effect occurs in volunteers who are
living at home instead of at our research facility," says Hawkes.
Studies at other institutions have shown that very high levels of selenium
result in lower sperm motility in laboratory animals. But results from
human studies have been inconsistent, Hawkes says. His collaborator
for the sperm motility studies is urologist Paul J. Turek, M.D., at
the University of California at San Francisco.
Another apparent effect of high selenium that occurred in the first
phase of the study was a small but statistically significant average
weight gain of approximately 2 pounds. The weight gain, Hawkes says,
accompanied a 25-percent decrease in active thyroid hormone. That's
why, in this phase of the study, Hawkes and his co-researchers are monitoring
changes in weight, thyroid hormones, and body compositionthe relative
amount of fat and lean tissue (muscle, bone, and water). He is doing
this work with exercise physiologist Marta D. Van Loan and with research
chemist Nancy L. Keim, both of the nutrition center.
Hawkes expects to see variations in the way the healthy men in his
study respond to selenium. Genes likely play a significant role in these
variations. So Hawkes and pathologist Jeffrey P. Gregg, M.D., of the
University of California at Davis Medical Center, are analyzing genetic
material in the volunteers' blood samples. Each sample is analyzed for
"We are looking for differences in the expression of genes due
to selenium," says Hawkes. "This work could provide valuable
clues to the inner workings of selenium."By Marcia
Wood, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program
(#107) described on the World Wide Web at http://www.nps.ars.usda.gov.
|"Selenium's Secrets Probed in New Study" was published in the March 2002 issue of Agricultural Research magazine.|