Boosting boron could be healthful. (Science News of the week).

It's hard to ignore the body's need for major nutrients--proteins, vitamins, and even fats--but most people give no thought to the diet's large cast of bit players. These include trace minerals, such as boron. Last week, scientists reported why U.S. diets tend to have relatively little boron and described health risks--including cancer--that may stem from overlooking this micronutrient.

Several years ago, Charlene J. Rainey of Food Research in Costa Mesa, Calif., conducted a six-nation comparison of dietary boron for the World Health Organization. Consuming a little over 1 milligram per day, U.S. adults took in 7 to 10 percent less boron, on average, than did people in Britain and Egypt and between 32 and 41 percent less than Germans, Kenyans, and Mexicans did.

Zuo-Fen Zhang of the School of Public Health at the University of California, Los Angeles was curious about whether the low U.S. boron intake might have health effects. He decided to mine data collected from thousands of men and women during a National Health and Nutrition Examination Survey (NHANES).

Zhang's team grouped participants according to the amount of boron in their diets. Key to discerning that amount, explains team member Curtis D. Eckhert of UCLA, was Rainey's new database on boron in foods. The team applied it to what each NHANES participant had eaten over a 24-hour period.

What "unexpectedly popped out" of the analysis, Eckhert says, was a finding that risk of prostate cancer falls as boron intake climbs.

By comparing the diets of 7,651 older men without prostate cancer with the diets of 76 men who had the disease, a strong dose-response trend emerged, Zhang reported last week in Orlando, Fla., at Experimental Biology 2001. The prostate cancer risk for men eating the most boron, at least 1.8 mg/day, was less than a third that of men eating under 0.9 mg/day.

Relatively high quantities of boron offered no protection against other malignancies or chronic diseases tracked, "so the association we observed is very specific to prostate cancer," Zhang says.

At the same meeting, Curtiss D. Hunt and Joseph P. Idso of the Agriculture Department's Human Nutrition Research Center in Grand Forks, N.D., offered animal data showing immune benefits from diets supplying the equivalent of 2 mg of boron in a person's diet per day.

"Inflammation is important in fighting many diseases," Hunt says. But uncontrolled, it "can trigger an immune chain reaction." In autoimmune diseases, such as rheumatoid arthritis, the body can't shut down such a chain reaction, which leads to tissue destruction.

Hunt's group had shown that rats were more susceptible to laboratory-induced autoimmunity if their diets were low in boron. The new data show that adequate boron prevents the activation of T-suppressor and T-helper cells, both of which are important in autoimmune chain reactions. Boron "appears to keep them in a [background] state," says Hunt.

His group has begun a 6-month study of the effect of dietary boron on pain in people with rheumatoid arthritis. During half the trial, people with the disease will eat 2 mg boron/day, an amount routinely consumed by only about 5 percent of U.S. adults. For the other half of the trial, participants will eat 0.2 mg/day.

Because large amounts of boron can be toxic, Hunt recommends aiming for no more than 2 to 3 mg/day. A glass of wine, a handful of peanuts, and a serving of noncitrus fruit--each offers close to 0.5 mg boron, Rainey says. In fact, her data show, it's because U.S. adults eat so few fruits and nuts that their boron intake tends to be low.