viernes, 12 de julio de 2019

Chemicals in Cosmetics, Soaps, Perfume, and Early Puberty

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By Dr. Liji Thomas, MDReviewed by Dr. Jennifer Logan, MD, MPH

The issue arises because some of the chemicals used in these products are potential or known endocrine disrupters (hormonal disruptors), which act at low concentrations on physiological processes. If so, using chemicals like these, in addition to the inevitable baseline or environmental exposure, could add up to a significant risk.

Women generally use more of these products than men and are a high-risk population on that account, especially cosmetologists and hair dressers. One study found higher odds of infertility among the former set of professionals. However, we do not know which chemicals, if any, may be driving this phenomenon.

A study in the US attempted to answer this question at least in part. They examined the levels of chemicals found in common household products, cosmetics, and hygiene products, in two sets of people: first, in pregnant women, and then in the children born from these pregnancies, at age 9 years.

Image Credit: Seika Chujo / Shutterstock

When the children were 9, they gave a urine sample and had their weight and height recorded. They were then reviewed periodically for signs of puberty from age 9 to 13, including breast development, pubic hair and periods in girls, and testicular development and pubic hair in boys.

What chemicals were involved?

The chemicals measured in this study included the following:

Diethyl phthalate
Triclosan
2,4 and 2,5 dichlorophenol
benzophenone-3
Methyl paraben
Propyl paraben
Triclosan breakdown products

Diethyl phthalates are used in fragranced shampoos, artificial perfumes and deodorants. Di-n-butyl phthalate and di-isobutyl phthalate are found in nail polish and in certain cosmetics, and have estrogenic and anti-androgenic properties as shown in animal studies and in vitro studies.

Parabens are commonly used as preservatives in certain cosmetics. These also have weak estrogenic and anti-androgenic activity in animal models and in vitro.

Triclosan and the dichlorophenols are antibacterial agents incorporated into some hand soaps, shaving creams, acne creams, deodorants and toothpastes. These phenols might cause thyroid hormone changes, or weak estrogenic effects like uterine enlargement, respectively.

Benzophenone-3 is present in some sunscreens, lip balms and cosmetics. In vitro studies with benzophenone-3 have shown it promotes proliferation of human breast cancer cells.

90% of products contained these chemicals, except for triclosan (about 70%).

What did the researchers find?

Girls whose mothers had higher levels while pregnant, or who showed higher levels in their urine by age 9, attained some of these puberty milestones up to 2 months in advance of other girls. In this study, the average age of onset of menstruation was 11.7 years.

Early onset of puberty is important because it is linked with a slightly higher risk of breast and ovarian cancer/testicular cancer in women and in men, respectively.

The following list shows the link between the onset of a physical sign and the chemical involved.

Monoethyl phthalate – pubic hair earlier by 1.3 months
Triclosan – menarche (onset of menstruation) earlier by 0.7 months
Dichlorophenol – menarche earlier by 0.8 months
Methyl paraben – in girls, breast development earlier by 1.1 months, pubic hair by 1.5 months earlier, menarche by 0.9 months
Propyl paraben – in boys, testicular and genital development earlier by 1 month

Was early puberty because of the chemicals?

There is more than one possible explanation for the association between chemical exposure and earlier pubertal development in this study. Rather than the chemicals being the cause of the earlier puberty, it could be that children who mature faster are more likely to use cosmetics and other body care products.

However, the study raises the question whether the ubiquitous use of household products containing these chemicals could be affecting human reproductive hormones. This could form part of the explanation for the early occurrence of pubertal changes in this cohort.

Some limitations were present in this study. Only 3 chemicals were measured in the form of their metabolic products, which are rapidly broken down in the blood, offering room for error. This also means we can’t get a good picture of exposure over the period leading up to puberty. All the children were of the same ethnic group, so the study may not apply to all children.

Phthalates and early puberty

Other chemicals commonly used in personal care products include dibutyl phthalates, talc, butylated hydroxytoluene (BHT), formaldehyde, and polyethylene glycols (PEGs). These do affect ovarian or reproductive function in women, as epidemiological, animal and mechanistic studies show. This supports the possibility that chemical exposure is pushing down puberty age.

Another study measuring high molecular weight (HMW) phthalates in correlation with body size, pubic hair and breast development found that as levels of phthalate diester metabolites rose, pubertal age increased in females. A tenfold rise delayed puberty by 9.5 months on average. Other studies have also shown links between increased HMW phthalates and delay in age at pubertal onset.

However, scientists wonder if the delay in puberty associated with hormonally active chemicals like HMW phthalates is real or apparent. It is possible that the influence of these chemicals on earlier pubertal age is not recognized because of the overriding presence of obesity. Many studies show that obesity reduces the age of puberty in girls.

Phthalate exposure in infancy and early childhood has been linked to obesity in girls beginning between 4 and 6 years. It is also related to a higher kisspeptin level which is a marker of puberty onset. It is quite plausible that these chemicals have estrogenic action.

Low molecular weight (LMW) phthalates were also studied in the same experiment, and showed a strong association with earlier pubertal age before adjustment for BMI. This study points out that phthalates do affect reproductive function.

Further research is needed to determine how exposure at different ages affects the outcome, and if the effects persist long-term, and whether exposure during pregnancy creates greater effects when reinforced by childhood exposure. The earlier the exposure, the greater may be the impact due to the increased vulnerability of the developing reproductive systems of childhood, or due to prenatal mechanisms that operate at very young ages.

Sources

Nhs.uk. (2018). Chemicals in cosmetics and perfumes linked to earlier puberty in girls. www.nhs.uk/.../
Harley K. G. et al., (2019). Association of phthalates, parabens and phenols found in personal care products with pubertal timing in girls and boys. Human Reproduction. https://doi.org/10.1093/humrep/dey337
Wolff M. S. et al., (2014). Phthalate exposure and pubertal development in a longitudinal study of US girls. Human reproduction. https://doi.org/10.1093/humrep/deu081
Chung-Yu C. et al., (2013). Phthalates may promote female puberty by increasing kisspeptin activity. Human Reproduction. https://doi.org/10.1093/humrep/det325
Vafeiadi M. et al., (2018). Association of early life exposure to phthalates with obesity and cardiometabolic traits in childhood: sex specific associations. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2018.00327
Aksglaede L. et al., (2009). Age at puberty and the emerging obesity epidemic. PLoSOne. https://doi.org/10.1371/journal.pone.0008450