A recent study of 3,400 Chinese adults, age 40 and over, has found that exposure to bisphenol A is not associated with an increased risk of developing diabetes. Bisphenol A is a chemical used in plastics that has been surrounded by controversy since some claimed it was responsible for health problems. The findings were published in the journal “Annals of Internal Medicine.”

The results of the study found that there was no correlation between levels of bisphenol A (better known as BPA) in the urine of study participants and their chances of having diabetes.

The 25% of the study participants with the highest urinary levels of BPA were found to have a higher risk of diabetes than those with a lower concentration of the chemical. However, the researchers did not find a “dose-response” relationship between BPA and diabetes — meaning that they did not discover any evidence that risk of developing diabetes increased as urinary BPA levels increased. The researchers said that, ultimately, they are unable to conclude whether there was a connection between BPA and diabetes.

Despite the research team’s findings, many are not convinced that they have put the issue to rest. Researchers outside the team have questioned the conclusions that they reached.

BPA is an endocrine disruptor: a chemical that can have a negative impact on normal hormonal activity in the human body. It’s also hard to get away from — it has been used for decades in the manufacture of hard plastics and linings for metal food and drink containers. Previous research has suggested that the large majority of Americans — about 95 percent — have some level of BPA in their blood.

Studies conducted recently on animals have suggested that BPA could contribute to certain types of cancer and heart disease and that it could affect neural development in children. Since the controversy around the chemical arose, the major manufacturers of bottles and cups for infants have stopped using it in the manufacture of those products.

Still, the effect of BPA on humans is unknown and remains controversial. In two large studies, elevated levels of BPA were found to be linked to increased risk of heart disease, while a study conducted in 2008 showed that individuals with higher BPA concentrations were at a higher risk of developing diabetes. Despite the associations, however, a causal relationship between the chemical and those conditions has not been proven — only a correlation.

The study analyzed data from 3,423 men and women; 32% of the participants had Type 2 diabetes. The participants were divided into four groups according to the levels of BPA in their urine. The group with the highest percentage of BPA was 37% more likely to have diabetes than the group with the lowest levels of BPA. However, the group with the second-highest concentrations of BPA showed no increased risk of diabetes while the next lowest group did show an increased risk.

Dr. Guang Ning with Shangai Jiao-Tong University School of Medicine, head of the study, stated that there was no “clear, monotonic relationship” between the presence of BPA and an increased risk of diabetes. “The evidence was not sufficient enough to declare an association,” said Ning.

However, an editorial published along with the study stated that the approach the researchers took was “idiosyncratic” because it all but dismissed the group with the highest levels of BPA and the highest risk of diabetes.

“It would be great to see the data released to the wider scientific community,” said Tamara Galloway, professor at the University of Exeter in the United Kingdom and an editorial writer for the study.