We need a precautionary principle approach or a lot more of these studies, and soon, in order to protect our children.
A long-running study started in the previous millennium aimed to find an answer to the question of whether exposure to phthalates, parabens and other phenols while in the womb or as a young child affects the age when puberty starts. 338 pregnant women were enrolled in the study in 1999-2000 and their children were followed carefully between ages 9 and 13 to establish the onset of puberty.
A previous study, the National Health and Nutrition Examination Survey (NHANES) in the US, found detectable levels these chemicals in the bodies of more than 96% of women studied. As detection limits have gotten consistently lower, detected does not mean the same thing as hazardous levels - but the prevalence of these chemicals in our lives demands answers defining safe levels and determining where we need to take care.This study, by a team of researchers from the University of California, Berkeley, together with a local pediatrics practice and representatives of the Centers for Disease Control, found no effects on the onset of puberty in young boys. But in the words of lead author, Dr. Kim Harley,
'We found evidence that some chemicals widely used in personal care products are associated with earlier puberty in girls. Specifically, we found that mothers who had higher levels of two chemicals in their bodies during pregnancy – diethyl phthalate, which is used in fragrance, and triclosan, which is an antibacterial agent in certain soaps and toothpaste – had daughters who entered puberty earlier. We also found that girls with higher levels of parabens in their bodies at the age of nine entered puberty earlier. This is important because we know that the age at which puberty starts in girls has been getting earlier in the last few decades."
Importantly, the study was able to find a dose-response relationship in the data: every time the concentration of a chemical in the mother's urine doubled, the onset of puberty shifted earlier at a consistent rate. Demonstrating such a dose response helps support the hypothesis that the chemicals do cause or contribute to the effects. The fact that the chemicals studied mimic female hormones could explain the lack of effects on boys.
These are chemicals known as "endocrine disruptors" - commonly suspected in a growing fertility crisis, linked to obesity and disease, and potentially behind findings of a gender gap in frogs. In short, this is serious stuff.
And yet, the category of "endocrine disruptors" is not effectively regulated. This is mostly because it is hard to prove effects are caused by specific chemicals. In particular, effects may be seen only long after exposure occurred. The European Union currently leads the field in action on endocrine disruptors, including application of the Precautionary Principle, but critics accuse even the EU of not treating the risks with sufficiently aggressive policies.
Consequently, long-running studies have great value. Unfortunately, this study suffers from some serious limitations. First, the study took only a couple measurements of the chemicals; because these chemicals are eliminated from the body quickly the couple samples may not be representative of continuous exposure. Second, the mothers in this study were selected due to potential for exposure to farm chemicals like pesticides; because they represent a specific social strata and community, the results may not be generalizable to all populations.
There are also many naturally occurring endocrine disruptors as well as other potential explanations, so even a long term study like this one must be supported by the weight of a lot more evidence before specific conclusions can be reached - especially if definitive proof of the risk is the standard of regulation, as it is in the USA. Weight of evidence means more studies until the truth is overwhelmingly clear and authorities can take action to protect human health.
Read the full study in the journal Human Reproduction: Association of phthalates, parabens and phenols found in personal care products with pubertal timing in girls and boys (https://doi.org/10.1093/humrep/dey337)