Posted: Dec 5, 2011 8:55 PM
Dec. 5, 2011 -- On the heels of new revelations about arsenic in grape and apple juice, a new study shows that rice may be a significant source of arsenic in the diets of pregnant women.
Exposure during pregnancy is a concern, experts say, because arsenic is able to cross the placenta and may harm a developing baby.
For the study, researchers measured arsenic levels in the urine of 229 pregnant women in New Hampshire, a state where 40% of people get their water from wells. Well water sometimes has higher levels of arsenic than water from municipal systems, which must meet federal safety standards.
Researchers checked the women's tap water for arsenic. They also asked the women to write down what food they had eaten in the three days before their urine tests.
Even after accounting for arsenic in drinking water, researchers found that women who had recently eaten rice had slightly higher levels of inorganic arsenic -- the toxic form -- in their urine, compared to women who had not eaten rice.
"Rice, which I think a lot of people would think of as very healthy, may be a real source of exposure to inorganic arsenic, above and beyond drinking-water arsenic," says Michael S. Bloom, PhD, an assistant professor at the University at Albany in New York.
Bloom is studying the health effects of chronic arsenic exposure. He was not involved in the current research.
For the average person, that means "you may be receiving an additional daily dose through rice. It adds to the cumulative burden of inorganic arsenic exposure," Bloom says.
Researchers calculated that women who ate just a half cup of cooked rice each day -- the average amount eaten in the study -- would be getting just as much arsenic as if they drank a liter of tap water at EPA's maximum allowable limit for arsenic.
In a statement, the USA Rice Federation says that comparison is misleading because it fails to recognize that the arsenic in water is all inorganic, the toxic form. Some of the arsenic found in rice is organic, a kind that is believed to be harmless.
Each gram of rice the women ate was associated with a 1% increase in their arsenic levels. A gram of rice is about 48 grains.
What does that mean for health? Researchers aren't sure.
"Our study is really about exposure. We're not studying a health outcome. At least in this report," says Margaret R. Karagas, PhD, a professor of community and family medicine in epidemiology at Dartmouth Medical School in Lebanon, N.H.
"Whether or not this is a health threat is a really big question," Bloom says.
Studies have linked high arsenic levels in pregnant women to an increased risk of miscarriage. Exposure to arsenic in the womb has also been associated with lower birth weights in children and an increased risk of infant mortality.
Most of those studies were in developing countries, however, where women had arsenic levels that were 50 to 200 times higher than those seen in this study.
In fact, Bloom says, the levels of arsenic seen in the women in this study are on par with those found in the general U.S. population.
"Obviously, people don't eat rice and drop dead the next day. You're looking at probably a chronic effect on health," says researcher Tracy Punshon, PhD, a research assistant professor in the department of biological sciences at Dartmouth College.
Studies have shown, for example, that people with long-term exposure to arsenic have higher rates of skin, lung, and bladder cancers. Arsenic has also been linked to higher rates of cardiovascular disease.
"Here in New Hampshire, where I live, we have natural arsenic in the ground water, and what you see in people who don't test their water and filter out their arsenic, that has translated into a higher-than-average risk of bladder cancer in this state," Punshon tells WebMD.
She says much larger, longer studies will need to be done before the health effects are better understood.
"We're frantically studying what this means," she says.
In the meantime, experts say the findings will be most important to policy makers, who can take steps to help ensure public safety.
"Our findings, along with those of other studies, highlight the need to regulate arsenic in food and in rice," Karagas says.
"We don't want to stop people from eating rice, because a rice-based, sort-of Asian diet is much better for your overall health than, say, eating McDonald's and fries every day," says Punshon, who has tested different varieties of rice for arsenic.
She says people should be choosy about the kinds of rice they eat, though, and make sure it's not the only grain in their diet.
Rice grown in the United States, for example, has been shown to have higher arsenic levels than jasmine or basmati rice grown in Thailand or India.
Her studies have found that brown rice contains higher levels of arsenic than white rice, because arsenic concentrates in the outer layer of rice bran.
"What really worries me is that the gluten-free movement is using a lot of rice, specifically brown rice," Punshon says. Brown rice turns up in a lot of products like cereal, rice syrup, baking mixes, and crackers.
"If you replace all the grains in your diet with brown rice, you're putting yourself in a very unique exposure window," for arsenic, she says.
Other experts agree that a balanced approach is key.
"We don't want to scare people off rice," Punshon says. "It's still a healthy food."