The University of Rochester Medical Center study was published yesterday in the online edition of the journal Environmental Health Perspectives.
The research adds to the growing body of scientific evidence linking phthalates to health problems. The resulting regulatory and consumer fallout could eventually force food packagers to search for alternatives.
Previous scientific studies on humans have found that phthalates are associated with poor semen quality in men and subtle changes in the reproductive organs in baby boys.
This connection between phthalates and testosterone helped to establish a basis for the Univeristy of Rochester study, said Dr. Richard Stahlhut, the lead author.
The new research raises the suspicion that low-dose exposures to phthalates and other common chemicals may be reducing testosterone levels or function in men, and thereby contributing to rising obesity rates and an epidemic of related disorders, such as Type 2 diabetes, he said.
"Substantial declines in testosterone levels and sperm quality have been observed in the United States and other countries over the last several decades which and it urgently requires explanation," Stahlhut said. "While we can't say yet that phthalates are a definite cause, I am certain they are on the list of chemicals that demands careful study."
Stahlhut's research team hypothesised that phthalates might have a direct link to obesity, since low testosterone appears to cause increased belly fat and pre-diabetes in men.
They analyzed urine, blood samples and other data from the National Health and Nutrition Examination Survey (NHANES), a large, multi-ethnic, cross-section sampling of the US population.
The data is acquired routinely by the Centers for Disease Control and Prevention. Researchers reviewed data from 1999 to 2002, the most recent years that phthalates levels were available.
Of the adult men studied in NHANES, data had been collected on phthalate exposures for 1,451, including obesity and waist circumference.
Of these men, data was collected on 651 who had fasting glucose and insulin levels required to calculate insulin resistance.
More than 75 percent of the United States population has measurable levels of several phthalates in their urine, according to the study.
"Unfortunately, there's still a lot to learn about phthalates," Stahlhut said. "The more difficult issue is what combinations of common low-dose chemical exposures might be contributing to these problems."
The phthalate family of chemicals is used in a variety of products from cosmetics, shampoos, soaps, lotions, lubricants, paint, pesticides, and plastics.
Phthalates are a class of compounds used most commonly as a softener for products made with polyvinyl chloride (PVC). In the food industry phthalate compounds are most commonly used for plastic packaging materials. The most commonly used phthalate is DEHP.
Food contamination occurs because of the use of PCV in wrapping materials.
The European Food Safety Authority has regularly been assessing phthalates. In 2005 the agency re-evaluate five phthalate chemical compounds used in plastic packaging, resulting in the raising, lowering or maintainence of acceptable daily intake limits.
Last year Danish-based Danisco produces the plasticiser from hardened castor oil and acetic acid. It is colourless, odorless and completely biodegradable.
The plasticiser, which is being marketed under the brand name Grinsted Soft-N-Safe, can be used for PVC food and beverage packaging without the need to modify equipment, Danisco stated.
The class of chemicals have also been a key ingredient in fragrances and in nail polish. One kind of phthalate fixes the fragrance in perfumes and lotions, shampoos, make-up, nail polish and hairsprays.
Another type is used in nail polish to help prevent chipping and breaking.
In 2005 the European Parliament banned six phthalate softeners in PVC toys and childcare articles that can be placed in children's mouths.
A previous University of Rochester study found the chemical may harm the genital development of unborn baby boys.