It always pays to read the study! It really does, because popular accounts often misinterpret what researchers actually found and end up raising undue alarm. Of course it is raising the red flag of alarm that gets attention, and these days, with all sorts of bloggers scooting around to popularize their websites hoping to recruit advertisers, getting attention is what it is all about. Let's get down to a study that generated the headline: “Don’t Microwave Those Vegetables; It Could Lead to Diabetes.” As one would expect, that headline ricocheted around the Internet spawning all sorts of comments about the evils of microwave ovens and plastic dishes. First of all, the study referred to was not about microwaving leftovers, and second, the word diabetes was never mentioned. What researches did was to take some data about phthalate metabolites found in urine as measured on a single occasion to see if there was any association with blood pressure. They did find an association, albeit a weak one. There was a difference of 1-2 mm Hg in systolic blood pressure between low and high levels of phthalate metabolites, which is essentially insignificant for an individual but could have significance across a population.
Where do the phthalates come from? These chemicals are used extensively as "plasticizers" to soften hard plastics such as polyvinyl chloride (PVC) which is commonly used in food production equipment, floor tiles, blinds, furniture and packaging. So given the ubiquitous nature of PVC, it isn't surprising that trace amounts of phthalates end up in the urine. But microwave containers are not made of PVC; they are made of polyethylene or polypropylene which contain no phthalates. While some commercial plastic wraps are made of PVC, home plastic wraps and sandwich bags are usually made of polyethylene with no phthalates in sight.
There are other issues here too. Associations cannot prove cause and effect. Indeed, there may actually be reverse causation. People may have higher blood pressure because they eat a lot of processed foods which may harbour phthalates, but the increase in blood pressure may be due to other components such as salt or fat. Phthalates may be just a marker for processed food consumption. Furthermore, there are many kinds of phthalates and they have very different properties. Also, single measurements of substances in urine are always a problem because they may not be reflective of average values.
The bottom line here is that this study has nothing to do with microwave dishes or with diabetes. The only way any connection can be made to diabetes is through suggesting that high blood pressure can increase the risk of diabetes. But most assuredly, in spite of the headlines it generated, this study does not show that using plastics in a microwave oven could lead to diabetes.
