Diabetes: Phthalate exposure may increase risk in some women

• Phthalates are chemicals widely used in food packaging, cosmetics, and children’s toys.
• Research suggests they can interfere with hormone function, and that they are associated with obesity, allergies, and other health concerns in both children and adults.
• Phthalates may also increase insulin resistance, raising the risk of diabetes.
• Now, a study in women has shown that increased exposure to phthalates over a prolonged period may contribute to a higher risk of diabetes.

Plastics are everywhere, and they are extremely useful. They package our food and drink, they are in many of our clothes, and are also in our personal care products. They are even in the water we drink and the air we breathe in the form of microplastics.

While they may be useful, increasing scientific evidence is suggesting that some components of plastics may be harmful to human health.

Top of the potentially harmful list are phthalates, chemicals added to many plastics to make them flexible. Phthalates have been implicated in many health concerns, including endocrine disruption, obesity, allergies, and reproductive issues.

One hormone likely to be affected by phthalates is insulin, which controls blood glucose (sugar) levels and makes glucose available to cells. A study in adolescents found that increased urinary phthalate levels were associated with increased insulin resistance, which is often a precursor to type 2 diabetes.

Another study made similar observations in older adults, finding that exposure to one particular group of phthalates, diethylhexyl phthalates (DEHP), increased oxidative stress and insulin resistance.

Now, a longitudinal study published in The Journal of Clinical Endocrinology & Metabolism has found that women exposed to high levels of phthalates have an up to 63% increased risk of developing diabetes.

“The study subjects were chosen from a larger longitudinal study of midlife women to evaluate an association between phthalates in the urine and [the] development of diabetes. The study found an association between higher levels of certain phthalates and development of diabetes in white women, but not the other races studied — Black and Asian.”

– Dr. Ishita Prakash Patel, board-certified endocrinologist, Texas Diabetes and Endocrinology, not involved in the study

6-year study

Researchers from the University of Michigan School of Public Health studied 1,308 women from the Study of Women’s Health Across the Nation (SWAN) for 6 years.

All the women were aged between 42 and 52 years (median age 49.4 years), and not taking any exogenous reproductive hormones for the last 3 months — such as the birth-control pill or hormone replacement therapy (HRT) — when they enrolled in the study in 1996–’97.

The study looked at phthalate exposure and incident diabetes in these women in the 6 years between 1999–2000 and 2005–2006.

At the start, and in 2002–2003, all the women gave urine samples in PET (polyethylene terephthalate) tubes. PET is a plastic that does not release phthalates when stored at cool temperatures. The researchers froze the urine samples at -80 degrees Celsius until analysis in 2017–’18.

Using mass spectroscopy (HPLC-MS), the researchers measured the concentration of 12 different phthalates and phthalate metabolites in the urine samples.

Diabetes and phthalates

The women attended nine follow-up visits during the study. Researchers classified diabetes if a woman reported using antidiabetic medications, had a doctor’s diagnosis of diabetes, and/ or had fasting blood glucose greater than 126 milligrams per deciliter (mg/dL) for two consecutive visits.

In the 6 years of the study, 61 women (4.7%) developed diabetes. These women had significantly higher concentrations of all except two phthalate metabolites than women who did not develop diabetes.

“Our research is a step in the right direction towards better understanding phthalates’ effect on metabolic diseases, but further investigation is needed,” says co-author Dr. Sung Kyun Park, of the University of Michigan School of Public Health in Ann Arbor, MI.

No effect in Black or Asian women

When the researchers stratified their results by race/ethnicity, they found a positive association between phthalate metabolites and incident diabetes in white, but not Black or Asian women. The authors state that it is “unclear what might explain such racial/ethnic differences”.

Dr. Patel agreed that the reasons for this finding were unclear, telling Medical News Today that “[t]he findings could have been skewed by a selection bias — for example, missing many cases of earlier onset diabetes.”

“Another possible reason could be that products were administered differently, leading to some forms causing more harm than others,” she hypothesized.

The researchers note that those who were younger, Black, current smokers, or obese generally had higher concentrations of phthalate metabolites. They also note that of the women who developed diabetes, 89.9% had overweight or obesity at the start of the study.

Study strengths and limitations

Because it was a longitudinal study, the researchers could demonstrate that phthalate exposure occurred before diabetes diagnosis, suggesting a causative effect.

Also, the population of women in the study was diverse, with white, Black, Chinese, Japanese, and Hispanic women participating. However, the researchers noted that “given inconsistent associations across racial/ethnic groups and phthalate metabolites, a causal relationship between phthalates and diabetes remains uncertain.”

The researchers note several limitations of their study. First, phthalate concentrations in single urine samples may not reflect habitual exposure to phthalates.

Secondly, they relied on fasting glucose to diagnose diabetes. Thirdly, the follow-up time was relatively short, and the sample was relatively small. And fourthly, other environmental factors may have affected the results.

Mindful of these limitations, they call for more research into the impact of phthalates on glucose homeostasis and diabetes, saying that, “[g]iven widespread exposure to phthalates and the enormous costs of diabetes to individuals and societies, ongoing investments in the research on phthalates’ metabolic effects are warranted.”

Should you avoid phthalates?

Although this study cannot prove that phthalates cause diabetes, it does raise the possibility, and phthalates are known to have other health effects. The European Chemicals Agency states that they can “interfere with our hormonal systems and cause allergies.”

But avoiding phthalates is not always easy, as they are found in many plastics. However, some steps are being taken to reduce people’s exposure to phthalates.

Many countries have limited the use of phthalates in children’s toys and other products, as there is evidence that exposure in childhood may adversely affect normal development.

Recently, the Food and Drug Administration (FDA) limited the use of phthalates in food packaging, reducing the risk of these chemicals being absorbed into foods

And some cosmetic manufacturers are now using other ingredients in place of phthalates. People can check whether plastics contain phthalates by looking at the recycling information.

So perhaps, to be on the safe side, we should follow the advice of Dr. Patel:

“It is probably best to limit exposure to chemicals like phthalates, which can be absorbed through the skin or digestive system, as much as reasonably possible.”

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