Rice Bran Lowers Blood Pressure in Rats

Thousands of years ago, humans began discarding the outer layer of long-grain rice, preferring the polished white kernel beneath. Scientists in Japan have shown that this waste product of rice processing, called rice bran, significantly lowers blood pressure in rats whose hypertension resembles that of humans.

The team reports their findings in the March 8, 2006 issue of the Journal of Agricultural and Food Chemistry, published by the American Chemical Society, the world’s largest scientific society.

A commonly prescribed class of drugs called ACE inhibitors dilates the arteries of hypertensive patients and thus decreases their risk of stroke, heart attack and kidney disease. But the drugs can also carry side effects: chronic cough, allergic reactions, dizziness, even kidney problems.

What if some component of our diet could work in similar fashion, with few or no side effects? Researchers at Tohoku University and Japan’s National Research Institute of Brewing demonstrated that adding rice bran to the diets of hypertensive, stroke-prone rats lowered the animals’ systolic blood pressure by about 20 percent and, via the same mechanism, inhibited angiotensin-1 converting enzyme, or ACE.

"There’s much work being done on various bran fractions to nail down any health benefits," says the journal’s editor, James Seiber, Ph.D., who is also director of the U.S. Department of Agriculture’s Western Regional Research Center in Davis, Calif. "This particular paper caught my attention for two reasons: the potential of bringing a waste product like rice bran into beneficial use, and the way the group went about their study with good controlled experiments using an appropriate model."

It’s still not clear whether simply eating more brown rice, which retains some of its bran, would reduce the risk of heart disease. However, previous research in humans, as well as animals with high cholesterol, does suggest that certain fractions of rice bran can lower levels of unhealthy LDL cholesterol.

The Tohoku study adds anti-hypertensive activity to the picture, along with a host of other biochemical markers that track blood glucose (implicated in diabetes), lipid profile, kidney function and the harmful effects of free radicals.

For example, high levels of a marker called 8-OHdG indicate biological stress and genetic damage due to oxygen-based free radicals. The researchers found that rice bran, which contains various forms of the antioxidant Vitamin E, markedly lowered the rats’ levels of the peptide 8-OHdG.

"Oxidative stress plays an important role in the initiation and progression of cardiovascular diseases," explained lead author Ardiansyah, a Ph.D. candidate at the university’s School of Agricultural Science.

He added one more element to the research that is new: using enzymes to clip components of rice bran from its cell walls, rather than extracting a fraction with ethanol. "I think enzymatic treatment will be more suitable for applications if we’d like to use rice bran as a functional food," he said.

The researchers’ next step is to elucidate the mechanisms by which specific components of rice bran inhibit ACE and lower cholesterol.

The American Chemical Society - the world's largest scientific society - is a nonprofit organization chartered by the U.S. Congress and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.