Bisphenol A (BPA), already known to affect hormone activity in the body, may also increase a person’s risk of diabetes.

BPA has been used in the making of plastic containers, as well as linings of metal food and drink cans, for decades. In fact, most people have some amount of BPA in their blood, research suggests.

Its effects in humans are unknown, but animal studies have hinted that BPA may be linked to some cancers, heart disease and birth defects. In 2008, study participants with higher BPA levels also showed a higher risk of diabetes. Then, a Chinese study found no link between BPA and diabetes.

Now, a federal study conducted between 2003 and2008 among 4,000 U.S. adults, found that study subjects with the highest urinary BPA levels were also more likely to have diabetes. The findings were recently reported in the Journal of Clinical Endocrinology & Metabolism. Still, none of the findings to date prove that one causes the other.

"Since BPA measurements as well as diabetes diagnosis were conducted at the same time, we cannot say for sure that BPA exposure preceded diabetes development," said lead researcher Dr. Anoop Shankar, of the West Virginia University School of Medicine.

Long-term studies with diabetes-free adults are needed, according to Shankar.

People worried about BPA should avoid canned foods and food containers made of polycarbonate plastics -- especially when reheating food, since small amounts of BPA may leech out of the plastic and into the food during the heating process, experts say. Polycarbonate plastics can usually be identified by the recycling code "7." Manufacturers have discontinued using BPA in children's drinking cups.