Compound in Plastics Linked to Increased Risk of Insulin Resistance in Adolescents
Exposure to urinary metabolites of the phthalate compound di-isononyl phthalate (DINP), which is increasingly used in the manufacturing of consumer products, was linked to an increased risk of diabetes in adolescents enrolled in a cross-sectional analysis reported in the May issue of the Journal of Clinical Endocrinology and Metabolism.
“Our research adds to growing concerns that environmental chemicals might be independent contributors to insulin resistance, elevated blood pressure, and other metabolic disorders,” said study lead investigator Leonardo Trasande, MD, Associate Professor of Pediatrics, Environmental Medicine, and Population Health at NYU Langone Medical Center, New York, NY. A second study by the same authors showed a significant association between DINP and di-isodecyl phthalate (DIDP) metabolite concentrations and an increased risk for hypertension, as reported online in the July 8 issue of Hypertension.
Given evidence suggesting health risks related to exposure to plastics containing di-2-ethylhexylphthalate (DEHP), manufacturers voluntarily replaced DEHP with alternative compounds—commonly the phthalates DINP and DIDP—over the last decade, noted Dr. Trasande and coauthor Teresa M. Attina, MD.
Cross-Sectional Analysis of NHANES Data
To examine the effects of DEHP, DINP, and DIDP on insulin resistance, the authors examined data from 356 fasting adolescents age 12 to 19 years who participated in the 2009-2012 National Health and Nutrition Examination Survey (NHANES). Insulin resistance was defined as homeostatic model assessment of insulin resistance (HOMA-IR), using a cut point of 4.39 to define insulin resistance.
Each log increase in DINP metabolite was linked to a 0.08 increase in HOMA-IR (P=0.001), after adjusting for demographic and behavioral factors, diet, age, body mass index, and urinary creatinine. Patients in the third tertile of DINP urinary metabolite concentration had a significantly greater adjusted prevalence of HOMA-IR compared to patients in the first tertile (34.4% vs. 23.4%; P=0.033). In addition, the third tertile of DEHP urinary metabolite concentration was linked to a significantly higher adjusted prevalence of HOMA-IR compared with the first tertile (37.7% vs. 20.5%; P=0.003).
The authors note that future longitudinal studies are needed to confirm these associations and noted that causation cannot be inferred from a cross-sectional study. “An alternative explanation would be that insulin-resistant children have unhealthy eating behaviors, including more packaged food consumption, and thus have higher urinary levels,” the authors wrote. They plan to study the long-term effects of exposure to DIDP and DINP, in particular, during pregnancy and early childhood.
Association May Not Be Causal, Says the American Chemistry Council
“A great quantity of research has been conducted on phthalates by universities, government agencies, manufacturers, and independent laboratories. This research indicates that phthalates break down into metabolites within minutes after entering the body,” according to a statement to SpineUniverse.com from the High Phthalates Panel of the American Chemistry Council (ACC). “And, information collected by the Centers for Disease Control and Prevention over the last 10 years indicates that exposure from all sources combined is extremely low—much lower than the levels established as safe by scientists at regulatory agencies,” according to the panel.
“Although NHANES biomonitoring data are used to conduct cross-sectional studies (ie, correlating measured exposures with specific health effects); they are not appropriate for examining causal associations, especially for children across such broad age ranges, as in the present study. These age ranges represent very different patterns of metabolism, growth, development, activity and behaviors—all of which may confound either the results or their interpretation,” the ACC panel stated.
“At most, the study shows an association, not a causal relationship. The study fails to show that exposure to phthalates causes any particular effect, and the alleged statistical correlation was not even particularly strong,” the ACC panel stated.
July 23, 2015