The US Agricultural Research Service is launching a study to investigate the potential benefits of fortifying breads, pastas and other flour-based foods with the trace element selenium.
The ARS, run by the US Department of Agriculture, will research moderately high doses of selenium and their effects on human cardiovascular health, immune function and reproductive health.
It is hoped that the project, already in its second phase, will provide new, detailed information about the mineral.
More than 30 healthy men aged 18 to 45 will participate in the study. For one year, half the volunteers will take a daily capsule providing five and one-half times the RDA (recommended dietary allowance) of selenium in the form of high-selenium yeast. The other half will receive a daily placebo - a capsule containing only yeast and no selenium.
Samples of blood, urine, semen and other specimens will be provided for laboratory tests at regular intervals. Participants will also receive tests for cardiovascular function and several other health indicators. In addition, they will complete detailed records of their exercise, general health and the foods they have eaten during specific three-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," said Chris Hawkes, the scientist leading the experiment.
The first phase included 11 volunteers who lived at the ARS centre 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 only use the centre for tests.
Good sources of the mineral include seafood and meats and grains from regions with selenium-rich soils. Dairy products and vegetables can also be sources of the mineral.
Scientists have long been aware of selenium's role in growth and reproduction in animals. Previous research on animals has also indicated that the mineral keeps the thyroid active and functioning properly, and it is a powerful antioxidant.
However, Hawkes said that recent studies done on laboratory animals raised on selenium-deficient feed suggest that selenium helps fight cardiovascular disease.
Arteries in those animals did not properly expand and contract. This expansion and contraction, or vascular responsiveness, is vital for maintaining a healthy flow of blood.
"In our study, we are measuring the changes in vascular responsiveness by regularly monitoring the diameter and flow rate of the brachial artery in the upper arm," said Hawkes. "This is a standard test of vascular responsiveness."
He added: "We think a selenium-containing enzyme may be involved in signalling the artery to expand."
Hawkes noted that selenium is already being tested by medical professionals to fight AIDS, but that the exact interaction between selenium and the immune system in healthy people, such as those in the new study, is not known.
In the first phase of the study, it was found that selenium increased the antibody response to vaccinations and improved the growth of lymphocytes, a type of white blood cell.
In the second phase, Hawkes will monitor several 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 diary to document colds and other respiratory infections.
The volunteers' reproductive health will also be of interest because the first phase of the study indicated that a high-selenium regimen might lower sperm motility.
In addition, the team will monitor changes in weight, thyroid hormones and body composition - the relative amount of fat and lean tissue - as the first phase showed a small but statistically significant average weight gain of approximately two pounds.