By: Dr. Firuza R.Parikh & Ms. Maherra Khambaty
In today’s world, man-made chemicals have become a part of our daily lives. Exposure to environmental chemicals and metals – in the air, water, soil, food, and consumer products is omnipresent. The National Health and Nutrition Examination Survey from 2003-2004 stated that virtually every pregnant woman in the United States is exposed to at least 43 different chemicals. Scientific evidence suggests that numerous chemicals, both natural and man-made, interfere with the endocrine or hormonal system which adversely impacts on human health and reproduction. These chemicals are often referred to as Endocrine Disruptors or EDs. They are present in toys, plastic bottles, food packaging, pesticides, detergents, and fragrances. They are in the food we eat, and the air we breathe. Some EDs persist in the environment for decades without being broken down and they bio-accumulate through the food chain.
So why are Endocrine Disrupters such a problem? EDs did not exist before the 1930s. During the period between 1970 and the 1990s, the first human generation ever exposed to these chemicals during fetal life began reaching their own reproductive age, and subtle disruptions began to appear. EDs impacted a broad range of health issues, including, increase in breast, ovarian and prostate cancers; increase in immune and neurodegenerative diseases; increase in obesity and diabetes, and female and male reproductive health issues including fertility issues. They interfere with reproduction, development, and other hormonally mediated processes. Some EDs such as Dichlorodiphenyltrichloroethane (DDT) and Polychlorinated Biphenyls (PCBs) are called Persistent Organic Pollutants (POP) since they do not break down easily and remain in the environment for decades.
The common EDs are Bisphenol A (BPA) found in plastics, Phthalates in plasticizers, pesticides such as DDT as well as environmental and industrial pollutants. There is an alarming trend in reproductive health witnessed worldwide – a significant increase in reproductive disorders, decline in sperm counts and decline in female ovarian reserve. The Endocrine Society’s Second Scientific Statement in 2015 provides conclusive evidence regarding how EDs interfere with hormones and how that affects human reproduction.
BPA is an endocrine‐disrupting chemical formed in plastic bottles, protective eyewear, electronic equipment and food storage containers. Humans are exposed to BPA when the chemical leaches from these products, via ingestion, inhalation or dermal absorption. When we consume BPA, it enters the body in an active form that can weakly bind to estrogen receptors and mimic the effects of estrogen in the body.
Phthalates are used in some cosmetics and personal care products such as deodorants, hair spray, shampoos, soaps, skin creams, body lotions, lipstick, nail polish, makeup products and hair dyes to fix the scent and make it longer lasting. Phthalates are produced globally in high volumes and are found in higher levels in women compared to men. High molecular weight phthalate is primarily used as a plasticizer in polyvinyl chloride (PVC) plastics to make them soft, flexible and durable. They are found in food plastic wraps, plastic toys, medical tubing, pharmaceutical coatings, vinyl flooring, adhesives, detergents, lubricating oils, and automotive plastics. They have lost chemical bonds in plastic products and hence can easily leach out into humans who are exposed to air, water, food.
DDT is currently banned in many countries. However, it is still is found in meat, fish, and dairy products. DDT is classified as a Persistent Organic Pollutant (POP) and can remain in the environment for up to 30 years. It accumulates in fatty tissues resulting in bioaccumulation and it undergoes bio-magnification as it moves higher up in the food chain.
The human endocrine system is one of our main communication networks. It is responsible for controlling and coordinating numerous body functions. It is composed of glands that release hormones and orchestrate processes such as growth, metabolism, sexual maturation & reproduction. The perfect balance in the endocrine system is extremely important in women because the menstrual cycle and fertility are very sensitive to hormonal imbalances. EDs can alter the delicate androgen-estrogen balance required for proper reproductive function by mimicking the hormone and thereby blocking the hormones. Thus, they disrupt the enzymatic pathways involved in hormone synthesis and metabolism, thereby disrupting reproductive hormones and function.
EDs have a significant impact on the female reproductive function. BPA and Phthalates are ovarian toxicants, with the ability to disrupt normal ovarian functioning and cause Premature Ovarian Failure (POF) through impaired oocyte maturation and lack of ovulation (anovulation). EDs alter ovarian steroidogenesis resulting in inadequate levels of necessary progesterone and estradiol to support the pregnancy. Women exposed to higher levels of BPA & Phthalates are at an increased risk of miscarriages. Women undergoing in vitro fertilization (IVF) risk low or failed fertilization, reduced or poor-quality oocytes and embryos, and implantation failure.
The reproductive system is regulated by the hypothalamic-pituitary-gonadal (HPG) Axis, to promote ovulation, follicular maturation and the synthesis of ovarian estrogens. EDs can disrupt this axis resulting in hormonal imbalances of estrogen and progesterone. These may affect the menstrual cycle, ovulation, and pregnancy.
Reproductive developmental periods, especially prenatal and early postnatal life and puberty, are vulnerable periods for high sensitivity to EDs exposures. The effects of EDs are transgenerational i.e. it can go through several generations.
A number of human studies provide evidence for BPA and Phthalate induced female infertility. The Environment and Reproductive Health (EARTH) Study, The Longitudinal Investigation of Fertility and the Environment (LIFE) Study, and, The Study of Metals and Assisted Reproductive Technologies (SMART) Study are some such studies. However, it is often difficult to replicate results in an epidemiological study as a number of factors come into play, including, the fact that humans are exposed to numerous EDs, sometimes making it difficult to identify specific effects of an ED. The impact of any ED on sexual development and reproduction potency depends on the time of exposure (e.g., in utero, newborn babies, adolescents, adults, menopausal women).
It is only over the last few years that scientists have understood the negative impact of EDs on the female reproductive system. It will be the combined effort of scientists, and Governments to limit the use of EDs so that our future generations are not affected. We should use the Precautionary Principle – an evolution of the ancient medical principle of “first do no harm” – to ban or restrict BPA usage to reduce exposure and resulting long – last adverse health effects.
Dr. Firuza R.Parikh is the Director, Department of Assisted Reproduction & Genetics, Jaslok Hospital & Research Centre, Mumbai, India, and Ms. Maherra Khambaty works at the Department of Medical Research, Jaslok Hospital & Research Centre, Mumbai, India.