Diabetes Linked to Phthalates

Phthalates, which are found in common plastics, cosmetics, and even some pharmaceuticals and medical devices, have been associated with the development of diabetes among seniors in Sweden, according to a study published online April 12 in Diabetes Care.

The investigators found that the 3 phthalate metabolites they studied were associated with a 25% to 30% increase in the risk for diabetes.

P. Monica Lind, PhD, associate professor of environmental medicine at the Section for Occupational and Environmental Medicine, Uppsala University, Sweden, and colleagues analyzed records of 1016 people aged 70 years or older who were involved in a study named the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) between 2001 and 2004.

During the PIVUS study, researchers asked participants about their medical history, exercise and smoking habits, and education. In addition, during mornings after overnight fasts, the participants gave blood samples for analysis of blood fat and glucose levels. For the purposes of the study, the researchers defined diabetes as a history of diabetes or a fasting glucose value higher than 7.0 mmol/L.

Of the 1016 participants, 119 had diabetes, and 88 of them had a history of diabetes for a mean of 8.9 years. Four participants reported having diabetes for more than 20 years.

When researchers in this study analyzed the serum levels of phthalate metabolites for the participants, they found that 4 of 10 metabolites were detectable in at least 96% of the people with diabetes, and that the 4 phthalate metabolites are commonly used in personal care fragrances. The metabolites are mono(2-ethylhexyl) phthalate, monoethyl phthalate (MEP), monoisobutyl phthalate (MiBP), and monomethyl phthalate (MMP).

After adjusting for sex, body mass index, smoking and exercise, cholesterol and triglycerides, and education, the researchers found that 3 metabolites were associated with a higher prevalence of diabetes (MEP: odds ratio [OR], 1.28; 95% confidence interval [CI], 0.97 - 1.7; P = .089; MiBP: OR, 1.30; 95% CI, 1.10 - 1.55; P = .003; and MMP: OR, 1.21; 95% CI, 1.00 - 1.46; P = .052 after multiple adjustments). They also found that MEP and MiBP were significantly related to diabetes prevalence after adjusting for sex only (OR, 1.30 [95% CI, 1.00 - 1.69] and 1.25 [95% CI, 1.07 - 1.46], respectively), and that MiBP's significance remained after the multiple adjustments.

The metabolites are related to either poor insulin secretion or insulin resistance, which are independent risk factors for developing diabetes. Phthalate metabolites are known to affect glucose stability in humans, the researchers write, and could be disrupting the biological pathways that contribute to glucose metabolism.

"Although our results need to be confirmed in more studies, they do support the hypothesis that certain environmental chemicals can contribute to the development of diabetes," Dr. Lind said in a news release.

"However, to find out whether phthalates truly are risk factors for diabetes, further studies are needed that show similar associations. Today, besides the present study, there is only one small study of Mexican women. But experimental studies on animals and cells are also needed regarding what biological mechanisms might underlie these connections," she added.

The researchers note that their study was limited to a sample of elderly white people and may not apply to other ethnic or age groups. They also note that a possibility of reverse causation exists, and that urinary analysis of phthalates is more common than the serum measurements used in this study.

However, for seniors at normal levels of exposure to chemicals such as phthalates, this "study showed that several phthalate metabolites are related to diabetes prevalence, as well as to markers of insulin secretion and resistance," the researchers conclude.