People who eat more rice have higher levels of arsenic in their systems, a new study finds. The findings suggest eating rice may expose some people to potentially harmful levels of arsenic.
The study, which was conducted in pregnant women, found that consuming just over one-half of a cup of cooked rice is equivalent to drinking 34 ounces (one liter) of water containing maximum amount of arsenic allowed by the federal limit (10 parts per billion).
The findings suggest some cultural groups may have higher arsenic exposures through rice than others, the researchers say. The average American eats about one-half of a cup of cooked rice per day, while consumption among Asian Americans exceeds two cups per day, the researchers said.
The findings come shortly after the release of test results by Consumer Reports showing potentially unsafe levels of arsenic in apple juice. The results also cited concerns over arsenic levels in rice, particularly the rice in infant cereals.
Chronic exposure to low levels of inorganic arsenic has been linked to increased risks of bladder,lung and skin cancer, as well as Type 2 diabetes and cardiovascular disease, according to the Environmental Protection Agency.
However, it's not yet clear whether the arsenic in rice, juice or other foods is harmful to people.
More research is needed to determine the health impact of exposure to arsenic in rice, the researchers say, but in any case, exposure in pregnant women is particularly concerning because of the potential risk to the unborn fetus.
Currently, the United States limits arsenic only in drinking water. The new study highlights the need to set limits for food, said study researcher Margaret Karagas, professor of community and family medicine at Dartmouth Medical School.
Arsenic in rice
Arsenic is a naturally occurring substance in the environment, and can also be present as the result of human activity, such as the use of arsenic-containing pesticides.
Karagas and colleagues analyzed arsenic levels in the urine of 229 pregnant women at a prenatal center in New Hampshire. Participants also kept track of their rice, water and fish consumption for three days before the urine sample was collected. Seventy-three participants ate rice during this period, eating half of a cup on average.
Women who consumed rice had higher levels of total arsenic and inorganic arsenic in their urine, compared with those who did not consume rice.
Each gram of rice consumed was associated with a one percent increase in total urinary arsenic, the researchers said.
The researchers did not measure arsenic levels in the rice itself, and these levels are known to vary considerably. The study will be published this week in the journal Proceedings of the National Academy of Sciences.
Rice plants are especially efficient at soaking up arsenic from their environment, both because of the plants' physiology and because the flooded areas in which they are often grown make it easier to take up arsenic compounds, Meharg said.
Research by Meharg has shown U.S. rice has some of the highest inorganic arsenic levels in the world.
Still, previous studies have found most arsenic in rice eaten in the United States is in the organic form, said Christopher States, a toxicologist at the University of Louisville in Kentucky who was not involved in the study. Because of this, the arsenic consumed in half a cup of rice suggested by this study "is not considered a hazardous level for an adult exposure," States said.
However, it's still possible that exposure to these levels could contribute to disease, States said. "We really do not know what a truly "safe" level is," States said.
Further, it's not clear how safe organic arsenic actually is.
"[It's] too simplistic to say that all organic arsenic is safe," said Carolyn Murray, an assistant professor of community and family medicine at Dartmouth Medical School. Research done in the late 1990s showed that high amounts of organic arsenic caused cancer in rats, the new study points out.
Exposures to arsenic early in life, as in the prenatal period, are probably more important because this is when humans are particularly vulnerable to disease development, States said. "These early life exposures may be the prime drivers of cancer," he said.
Exposure to arsenic through drinking water may also be a concern for some. Fourteen percent of participants in the had tap water that contained above 10 ppb of arsenic, the researchers said. A large fraction of New Hampshire residents commonly consume water from wells that is unregulated. Because of the risk of arsenic exposure, Karagas recommends people with private wells have their water tested for arsenic.