Higher levels of a chemical often found in plastic food and drink packaging are associated with cardiovascular disease and diabetes, a study has suggested.
The group with the highest levels of Bisphenol A (BPA) in their urine were found to be more than twice as likely to have diabetes or heart disease.
But the Journal of the American Medical Association research did not show that Bisphenol A caused the conditions.
And a UK toxicology expert stressed the study's findings were "preliminary".
Over two million tonnes of BPA were produced in 2003, although usage of the chemical is starting to decline.
As well as being present in packaging, people are exposed to BPA through drinking water, on their skin and in household dust.
Previous research in the US found detectable levels of BPA in more than 90% of the population.
Animal tests had raised concerns about the possible effects in humans - such as disruption to hormone production - but were inconclusive because people process the chemical differently.
The study by researchers from the UK's Peninsula Medical School in Exeter looked at BPA levels in the urine of 1,400 US adults, and whether they had ever been diagnosed with one of eight major diseases, including arthritis, stroke and thyroid disease.
No strong link was found aside from that with cardiovascular disease and diabetes, although higher BPA concentrations were associated with clinically abnormal concentrations of three liver enzymes.
People who were obese, and therefore already at a higher risk of cardiovascular disease and diabetes, had higher BPA levels - and the researchers said it was possible that eating more was simply linked to a higher intake of the chemical.
But they said the link between higher levels of the chemical and the conditions remained true, even when they took body mass index levels and waist measurements into account,
Dr David Melzer, who led the study, said: "These findings add to the evidence suggesting adverse effects of low-dose BPA in animals.
"Independent replication and follow-up studies are needed to confirm these findings and to provide evidence on whether the associations are causal."
He added: "Given the substantial negative effects on adult health that may be associated with increased BPA concentrations and also given the potential for reducing human exposure, our findings deserve scientific follow-up."
The study is being published to coincide with a hearing on BPA by the influential US Food and Drug Administration (FDA).
A spokesperson from the UK's Food Standards Agency said an expert panel was keeping the safety of BPA under review.
"The FSA will continue to closely monitor scientific reports about the health effects of BPA in the body and will take action to further protect consumers if it becomes necessary."
Professor Alan Boobis, a toxicology expert based at Imperial College in London, said the study did not fit with previous research into the chemical.
"It's an interesting finding, which we can't ignore. But it is preliminary, and requires following up."
He added: "It may be that the association is the inverse of what they are suggesting; not that the BPA is causing cardiovascular disease and diabetes, but that these diseases result in a higher level of BPA, or that there may be a common cause - like something going wrong with the kidneys.
"Or it could be a chance finding."
Professor Richard Sharpe, of the University of Edinburgh, said for some people a raised risk of cardiovascular disease and diabetes could simply be down to drinking too many high sugar canned drinks.
These people would also be exposed to higher levels of BPA from the lining of drinks cans - but that could be purely incidental.
He said more research was needed to tease out the truth before BPA could be labelled as the prime suspect.
In a joint statement, the British Soft Drinks Association (BSDA) and the Food and Drink Federation (FDF) said bisphenol A had been approved as safe for use in food and drink containers by the regulatory authorities, and its use was closely monitored and regulated.
Levels of bisphenol A in food and drink can linings that did include the chemical were well below safety levels set by the European Food Safety Authority.