ROCKVILLE, Maryland, September 17 A major study links a chemical widely used in plastic products, including baby bottles, to health problems in humans like heart disease and diabetes, but US regulators said on Tuesday they still believe it is safe. The chemical bisphenol A, or BPA, is commonly used in plastic food and beverage containers and in the coating of food cans. Until now, environmental and consumer activists who have questioned the safety of BPA have relied on animal studies.But the study by British researchers in the Journal of the American Medical Association found that among 1,455 US adults, those with the highest levels of BPA were more likely to have heart disease, diabetes and liver-enzyme abnormalities than those with the lowest levels. US Food and Drug Administration officials said they would review the new findings commenting