Arsenic is odourless, tasteless and colourless and is a naturally occurring poison and carcinogen, it is found in ground water and is easily soluble in water.

Arsenic from inorganic sources is highly toxic and causes cancer in humans. Millions of individuals worldwide are exposed to drinking water contaminated with inorganic arsenic.

While exposure to high concentrations of the element in drinking water and in the workplace has been shown to be associated with diabetes, little is known about the effect of lower levels on diabetes risk.

Researchers suggest small amounts of arsenic may sicken people over a period of time.

In a study involving almost 788 American adults over the age of 20, participants with type 2 diabetes had a 26 percent higher level of total arsenic in their urine than those without the disease.

The participants had their urine tested for arsenic levels as part of a wider government health and nutrition survey.

The researchers from Johns Hopkins University in Baltimore say there was a "relatively strong" association between commonly found levels of arsenic in urine and type 2 diabetes and they suggest there may be no safe level of arsenic.

Dr. Ana Navas-Acien and colleagues say the problem is worldwide and as water becomes a scarce resource, additional sources will be needed.

Dr. Navas-Acien says arsenic raises the risk for cancers of the bladder, lung, kidney, skin and, possibly, the prostate, and 20% of the study participants who had the most arsenic in their bodies, had 3.6 times the risk of developing late-onset diabetes.

The study found levels of arsenic were 26% higher in people with late-onset, or type 2 diabetes than those without the disease.

The researchers say U.S. government limits for drinking water are 10 micrograms of arsenic per liter, which is exceeded in the water consumed by 13 million Americans living mostly in rural areas that rely on wells to bring up ground water.

This applies to many other countries and arsenic contaminates drinking water for millions of people in Bangladesh, parts of Central Europe, Chile, Argentina and the western United States, where ground water is the source of drinking water and the land has higher concentrations of arsenic.

Estimates suggest that 7.8 percent of Americans have diabetes, although some do not know it and at least 90 percent of cases are the type 2 variety and Dr. Navas-Acien says arsenic may play a significant role in diabetes incidence.

Arsenic can accumulate in the body, and can affect the body's ability to use insulin and perform the vital task of converting blood sugar into energy by blocking receptors, which allow glucose to enter the cells.

The research is published in the Journal of the American Medical Association.