Rice consumption linked to higher arsenic levels in pregnant women.

Feb 14, 2012

Gilbert-Diamond, D, KL Cottingham, JF Gruber, T Punshon, V Sayarath, AJ Gandolfi, ER Baker, BP Jackson, CL Folt and MR Karagas. 2011. Rice consumption contributes to arsenic exposure in U.S. women. Proceedings of the National Academy of Sciences http:dx.doi.org/10.1073/pnas.1109127108.

Synopsis by Renee Gardner

U.S. women who reported eating average-sized portions of rice had higher levels of arsenic exposure compared to women who didn’t eat rice, indicating that food may provide potentially harmful levels of arsenic.

Eating even relatively modest levels of rice - about a half a cup of cooked rice a day - can significantly contribute to arsenic exposure in the U.S. population, reports a study of pregnant women who live in New Hampshire.

Women who were exposed through both eating rice and drinking water had on average twice the level of arsenic in their urine than women who did not eat rice and were exposed only through water.

The results show the rice portions reported in the study contributed about the same levels of arsenic as drinking a liter of water containing 10 micrograms of arsenic. Ten micrograms per liter (μg/L) is the U.S. Environmental Protection Agency's (EPA's) upper limit for arsenic in drinking water.

It is unclear whether these levels of arsenic exposure would affect the health of the pregnant women or their developing children. But, to be safe and avoid unnecessary exposure in this vulnerable population, the researchers urge better monitoring of the rice sold in the United States.

Arsenic levels in food are not currently regulated in the United States. This means there is no limit on the amount of arsenic that rice or rice products sold in the United States – and also in Europe – can contain. In contrast, China has set levels for the maximum amount of arsenic allowed in rice sold there.

A toxic element, arsenic is associated with increased rates of cancer, diabetes and cardiovascular disease. Exposure during pregnancy is linked with increased rates of miscarriage and increased frequency of respiratory infections during infancy in Bangladesh, a part of the world with very high arsenic exposures.

Because groundwater dissolves arsenic that occurs naturally in soil, contaminated drinking water is a major source of exposure.  Arsenic "hot spots" – where groundwater contains high concentrations – occur all over the world due to geologic variation. Areas in the northeast and southwest United States are considered hot spots. Some plants – particularly rice – can take up arsenic from the soil.

In the United States, the average amount of cooked rice eaten per person per day is a half a cup. Hispanics, Asian-Americans and people affected by Celiac disease – who eat more rice because they can’t digest the gluten found in wheat – eat on average between two and three cups of cooked rice per day.

In this study, scientists investigated sources of arsenic exposure among pregnant women in New Hampshire, a state where high arsenic concentrations in well water are known to be a problem. Women near the end of their second trimester participated. The scientists measured arsenic in the women’s drinking water and in their urine. Arsenic passes through the body and into urine within a day. They also asked the women to report what they had eaten in the previous two days.

Fourteen percent of the women had levels of arsenic in their drinking water above the current EPA drinking water standard of 10 μg/L.

Of the 229 women participating in the study, 73 reported consuming rice within the previous two days. The women reported eating an average portion of 0.56 cups of cooked rice, similar to the country's national average.

The average arsenic concentration in the women’s urine was 4 μg/L. Women who reported eating rice in the previous two days had on average 2 μg/L more total arsenic in their urine compared to women who did not report rice consumption. These women also had a higher concentration of the most toxic form of arsenic – inorganic arsenic – in their urine. The scientists calculated that each gram of rice (about 1/100th of a cup of dry rice) consumed was associated with a 1 percent increase in the concentration of arsenic in the urine. 

Further studies are necessary to confirm these results and investigate if these levels affect health. For now, the association between eating rice and levels in the women's urine found in their study as well as the ability of rice to concentrate arsenic "highlights the need to regulate arsenic in food," the authors say in the published paper.

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