TUESDAY August 20, 2008 (foodconsumer.org) -- A new study by researchers at the Johns Hopkins Bloomberg School of Public health suggests that inorganic arsenic in drinking water may be a risk for developing type 2 diabetes.

The observational study showed that high levels of arsenic were more likely to be found in the urine of people with type 2 diabetes than those without.

The study titled "Arsenic Exposure and Prevalence of Type 2 Diabetes in US Adults" was released in the August 20, 2008 issue of the Journal of American Medical Association.

"Our findings suggest that low levels of exposure to inorganic arsenic may play a role in diabetes," said Ana Navas-Acien, MD, PhD, lead author of the study and assistant professor with the Bloomberg School's Department of Environmental Health Sciences.

"While prospective studies are needed to establish whether this association is causal, these findings add to the existing concerns about the long-term health consequences of low and moderate exposure to inorganic arsenic."

Inorganic arsenic is found commonly yet naturally in rocks and soils. Soil and irrigation water and drinking water can be contaminated with this toxic metal element.  

Most exposure in the U.S. to inorganic arsenic comes from contaminated drinking water, according to a press release by the Johns Hopkins.

The maximal tolerance for arsenic in drinking water set by World Health Organization is the same as the one by the U.S. Environmental Protection Agency, 10 parts per billion (PPB).    The EPA standard not long ago was 50 ppb, which had drawn criticism.

An estimated 13 million people in the United States live in areas where the concentration of inorganic arsenic in the public water supply exceeds standards of the EPA, particularly in the West, Midwest and Northeast regions, according to the Johns Hopkins press release.

For the current study, the researchers tested for the level of arsenic randomly selected urine samples from 788 U.S. adults age 20 or older who participated in a 2003 to 2004 National Health and Nutrition Examination Survey. And then they associated arsenic levels with risk of type 2 diabetes.  

After adjusting for diabetes risk factors such as body mass index and for organic arsenic compound found in seafood, the researchers found subjects in the top one-fifth of total urine arsenic levels (16.5 micrograms per liter) had 3.6 times the odds of having type 2 diabetes as those in the lowest one-fifth (3.0 micrograms per liter).

They also found subjects in the top one-fifth of dimethylarsinate levels (6.0 micrograms per liter) were 1.5 times as likely as those in the lowest one-fifth (2.0 micrograms per liter) to develop diabetes. Dimethylarsinate is a metabolite of inorganic arsenic before excretion.

The authors explained in their report that "The potential role of arsenic in diabetes development is supported by experimental and mechanistic evidence." Insulin-sensitive cells could be less efficient at metabolizing glucose after exposed to insulin and sodium arsenite compared to cells exposed only to insulin. Arsenic could also affect genetic factors to interfere with insulin sensitivity and other physiological processes.

In light of given widespread exposure to inorganic arsenic from drinking water worldwide, the finding of the association between exposure to inorganic arsenic and increased risk of type 2 diabetes may provide some suggestion as to what can be done to help prevent the health condition that affects nearly 20 million people in the U.S. alone.

Arsenic is best known for its carcinogenic effect.   It is less known for its association with diabetes.   In addition to drinking water, arsenic is also present in foods or products.

For instance, rice produced in California has high levels of arsenic.   A study led by researchers at the University of Aberdeen and published in the August, 2005 issue of Environmental Science and Technology found 260 parts per billion (ppb) of arsenic in US rice compared with 5 ppb in Indian basmati rice.

In the U.S., arsenic in organic form is commonly used to treat pressured wood, which is used to make wood stuff such as decks and wood fences to protect molds from "eating up" the wood.    Children who touch those arsenic treated wood products can get quite some arsenic in hands, according to early studies.

Also in the U.S., arsenic is used in poultry to prevent parasites from growing, a way to promote growth of chicken.    But research found the arsenic level in certain parts of chicken is two or three times higher than the level deemed to be safe.

Regardless, further studies are needed to prove or disprove that the association between arsenic and diabetes is a cause and effect relation.  The study per se did not mean to say high exposure to arsenic causes diabetes.