Article: Radke EG, Galizia A, Thayer KA, Cooper GS. 2019. Phthalate exposure and metabolic effects: a systematic review of the human epidemiological evidence. Environment International. DOI: https://doi.org/10.1016/j.envint.2019.04.040.
There has been a lot of controversy recently about a group of chemicals that are found, well, nearly everywhere: phthalates (pronounced tha-leit). Their ubiquitous presence in our environment combined with their toxic effects observed in lab studies, have fueled concerns that they might be negatively impacting our health.
What are phthalates, how are we exposed, and how can they harm us?
Phthalates are synthetic liquid chemicals that are used to make consumer and building products flexible and resilient. Phthalates can migrate from plastic containers, cosmetics, detergents, raincoats, vinyl flooring, etc. and enter humans when they consume or touch these products. Correspondingly, phthalates have been found in the blood and urine of many people, but they also leave the body quickly. They are believed to increase production of fat cells by interacting with a specific cell receptor. They are also known to disrupt the hormonal system.
In the U.S., three phthalates (DEHP, DBP, and BBP) have been banned from children’s products.
What’s our relationship with phthalates?
Recently, scientists at the U.S. Environmental Protection Agency collected to-date information on phthalates and rated the quality of all relevant studies published in the literature to determine if phthalates are contributing to diabetes, obesity, and kidney diseases in humans. Using something called an “odds ratio”, which informs the strength of association between the chemical and disease, the research team evaluated the risk associated with these chemicals. An odds ratio of 1 means there is no association between chemical and disease. A number greater than 1 indicates that the presence of the chemical increases the odds of the disease occurring (greater the number, greater the odds), and a number lesser than 1 indicates the opposite is true. In many of the studies that were analyzed, people were divided into four groups. Group 1 had the lowest exposure to phthalates and Group 4 had the highest exposure. The scientists determined the odds ratios of people in Groups 2, 3, and 4 by comparing their incidences of lifestyle diseases with that of people in Group 1.
Following exposure to two phthalates, DBP and DIBP, people in Group 4 typically had an odds ratio between 2 to 3 for type 2 diabetes and insulin resistance (which was determined by looking at glucose and insulin levels in blood). These chemicals produced an odds ratio of less than or equal to 1 for gestational diabetes (i.e., diabetes in pregnant women). Following exposure to phthalate DEHP, people in Group 4 had an odds ratio between 2 to 3 for insulin resistance but there was no significant association between phthalate concentrations and type 2 and gestational diabetes. People in Group 4 exposed to phthalate DEP had an odds ratio from 1.7 to 7.2 for gestational diabetes, and an odds ratio below 1 for type 2 diabetes and insulin resistance. Exposure to increasing levels of the phthalate BBP did not seem to increase incidences of type 2 diabetes, gestational diabetes, or insulin resistance.
The authors also ascertained there was inadequate evidence currently to conclude whether phthalates increased our risk of obesity or kidney diseases.
Important things to keep in mind
As with any paper, there are some nitty gritty details that need to be kept in mind. Though increased exposure to phthalates often coincided with increased disease incidences, in a few instances, the opposite was seen. As there are no biological mechanisms to explain this, it shows that one needs to be cautious when interpreting correlation data. Also, humans in the group with highest exposure could have developed lifestyle diseases from exposure to other chemicals or due to other factors that were not properly accounted for (for e.g., genetics, dietary/exercise choices, and better healthcare options).
In fact, the authors stated that only a few studies controlled for the diet of the human subjects. Regularly eating more-than-necessary food can increase diabetes risk. Similarly, regularly eating packaged and processed food (which are often unhealthier) also increases odds of developing diabetes and, since phthalates enter food from plastic packaging and containers, it can be difficult to separate the effect of food from phthalates. And in many instances, positive associations between increasing phthalate levels and diabetes risks were only seen in adults, not adolescents. Hence, before drawing conclusions, it is always better to verify correlation results by looking at other pieces of information: for example, do lab animals and cell cultures exposed to phthalates show similar responses?
Fortunately for us, the authors looked at this (i.e., compared the human data described above with published lab data) to determine if the evidence was strong enough to say phthalates contributed to increased diabetes risk. They concluded that there was “moderate” evidence to say that DEHP, DBP, and DIBP exposures increased diabetes risk. The evidence was “slight” for BBP, DEP, and DINP. They believed more research is needed to further clarify the relationship between phthalates and lifestyle diseases.