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Exposure to phthalates -- a type of endocrine-disrupting chemical -- was linked with a higher incidence of type 2 diabetes among women, but only those who were white, researchers reported.

In a study of over 1,300 women without diabetes, certain phthalate metabolites were associated with a higher incidence of diabetes during 6-year follow-up in a crude model, reported Sung Kyun Park, ScD, MPH, of the University of Michigan School of Public Health in Ann Arbor, and colleagues.

However, these associations disappeared after adjusting for age, race and ethnicity, location, education, menopausal status, physical activity, smoking status, and dietary energy intake, they noted in the .

But when broken down into three racial groups -- white, Black, and Asian women -- the risk for incident diabetes remained significant for white women only, even after adjustment.

Park's group found that for white women, each doubling of the concentration of five types of phthalates was linked with a 30% to 63% higher incidence of type 2 diabetes:

• Mono-isobutyl phthalate: HR 1.63 (95% CI 1.18-2.25)
• Monobenzyl phthalate: HR 1.57 (95% CI 1.18-2.09)
• Mono(3-carboxypropyl) phthalate: HR 1.50 (95% CI 1.06-2.12)
• Mono-carboxyoctyl phthalate: HR 1.43 (95% CI 1.05-1.95)
• Mono-carboxyisononyl phthalate: HR 1.30 (95% CI 1.03-1.65)

These are all considered high-molecular-weight phthalates, with the exception of mono-isobutyl phthalate, which is a low-molecular-weight phthalate.

Low-molecular-weight phthalates are commonly found in personal care products like perfume, nail polish, hair care, and feminine hygiene products, while high-molecular-weight phthalates are often used as plasticizers, such as for vinyl flooring, food packaging, and even clothing.

"Our research found phthalates may contribute to a higher incidence of diabetes in women, especially white women, over a 6-year period," said Park in a statement. "People are exposed to phthalates daily increasing their risk of several metabolic diseases. It's important that we address endocrine-disrupting chemicals now as they are harmful to human health."

"Our research is a step in the right direction towards better understanding phthalates' effect on metabolic diseases, but further investigation is needed," he added.

A slew of prior studies have linked exposure to this class of endocrine-disrupting chemicals to poor health outcomes, ranging from all-cause death, attention deficit-hyperactivity disorder, and shorter gestation, to name a few.

For this study, Park's group followed 1,308 women from the from 1999-2000 through 2005-2006. At baseline, median age was 49.4, and median body mass index was 25.5. The women resided in one of five metropolitan areas: Detroit, Boston, Los Angeles, Pittsburgh, or Oakland, California. About half where white, 20% were Black, 13% were Chinese, and 15% were Japanese.

In total, 11 phthalate metabolites were measured in spot urine samples. Over the 6-year follow-up, 4.7% of women developed incident diabetes. Park's group noted that around 2000, the prevalence of diabetes was about 4.2% for white women, but 11.4% for Black women, suggesting a potential selection bias.

"It is unclear what might explain such racial/ethnic differences," they wrote. However, they pointed out that because the sample only included women free of diabetes at baseline, all of whom were at midlife, this excluded those with pre-existing diabetes. It's possible that those who were excluded had higher levels of past phthalate exposure, the authors suggested.

"Because Black women are generally exposed to higher levels of phthalates and develop diabetes at a younger age than white women, this selection bias may have affected Black women to a greater extent, resulting in greater attenuations in the HRs for incident diabetes," they explained.

Because of this, more research is warranted to further investigate these racial differences, they said.

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