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Endocrine Disruptors

4. Do EDCs affect human health?

  • 4.1 What are the possible reproductive effects of EDCs in humans?
  • 4.2 What are other possible effects of EDCs?
  • 4.3 Do EDCs cause cancer in humans?
  • 4.4 What other factors must be considered regarding human health?

At the moment there is no firm evidence that environmental endocrine disrupting chemicals (EDCs) cause health problems at low levels of exposure. However, the fact that high levels of chemicals can impair human health through interferences with the endocrine system, raises concerns about the possible harmful effects of EDCs. Increases in the occurrence of certain diseases affecting the reproductive system in men and women have also raised the question of whether this could be due to exposure to EDCs. The difficulty in finding conclusive evidence on what is happening globally is compounded when researchers try to compare and integrate data about trends in human health from different sources collected at different times, and often using different methods under varying conditions.

Another major problem is the lack of information on EDC exposure during critical periods of early human development, which influence the way the body functions in later life. What is more, the amounts of hormones we naturally produce – and the strength of their effects – in our bodies are generally greater than those of foreign chemicals. However, overall, the biological plausibility of possible damage to certain human functions (particularly reproductive and developing systems) from exposure to EDCs seems strong when viewed against the background of known influences of endogenous and exogenous hormones on many of these processes. Therefore, despite the difficulties and uncertainties, concern remains about the possible role of exposure to EDCs in adverse health effects in humans. The examples in 4.1. illustrate these concerns. More...

4.1 What are the possible reproductive effects of EDCs in humans?

4.1.1 Reproductive effects:

  • Sperm quality: A number of studies report a decline (since the 1930s) in sperm quality – i.e. sperm count, proportion of normal sperm, semen volume – in several countries, which might be expected to affect fertility. But not everyone agrees with these results. Several surveys refute this downward trend in human sperm quality. Even if there is not a worldwide decline in sperm quality, there are clearly variations in sperm quality, both within and between countries. From what is known about testis development and function, it is plausible that endocrine-active chemicals could affect sperm quality. But so far, no research has studied the relationship between exposure to endocrine disrupting chemicals and sperm quality.
  • Fertility: Some human and experimental animal studies have shown that occupational or environmental exposure to high levels of certain chemicals, such as pesticides and PCBs, can impair fertility and increase the rate of miscarriages, but any relationship to endocrine disruption remains speculative.
  • Sex ratio: In a number of regions and countries, fewer boys than girls are being born. There is evidence that unidentified external influences are associated with such changes, but it is not known whether endocrine disruptors are involved.
  • Abnormalities of male sex organs: Increased numbers of birth defects in male sex organs have been reported. The abnormalities are cryptorchidism, a condition in which the testes remain inside the abdominal area instead of dropping down, and hypospadias, which is a malformation where the opening is on the underside of the penis instead of the end. The possible role of EDC exposure in these human malformations has not been investigated. However, experimental animal studies clearly show that a number of EDCs can disrupt development of the male reproductive system.

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4.1.2 Endometriosis: This is a disease affecting women where uterine tissue appears in parts of the abdomen other than the uterus, causing pain and infertility. The disease is made worse by oestrogens. Some reports have linked development of endometriosis in women to exposure to EDCs, such as dioxins. However, these findings are debatable. More...

4.1.3 Precocious puberty: Some studies have raised concerns about the possible influence of EDCs on the timing of puberty, or the process of sexual maturation. There is evidence from population studies that the age at which puberty normally occurs is becoming younger, but the reasons for this and the role of other factors, such as nutrition, need to be clarified. More...

4.2 What are other possible effects of EDCs?

4.2.1 Nervous system function: Information from human and experimental animal studies clearly shows that exposure to certain endocrine disrupting chemicals (EDCs), such as PCBs – particularly before birth – can harm the development of the nervous system, neuroendocrine function, and behaviour. Some of these effects appear to result from alterations in thyroid function or in the activity of the chemicals which carry messages between nerve cells. In the majority of cases, however, it has not been demonstrated that these effects are due to endocrine disruption. Similar effects can also result from exposure to chemicals that influence nervous system development, but have no known action on the endocrine system. More...

4.2.2 Immune Function: The immune system is involved in fighting infections and in allergic reactions. Exposure to environmental chemicals – including certain EDCs, such as DES, a powerful synthetic oestrogen, or PCBs and dioxins – has been shown to alter human and animal immunity. But it is not clear whether this occurs via endocrine disruption. More...

4.3 Do EDCs cause cancer in humans?

4.3.1 Cancer: The occurrence of certain cancers at hormonally sensitive sites in the body has been increasing over time in many industrialised countries. Although some of the apparent increases may be due to improvement in our ability to detect cancer, it does not explain all of the increases. This has led to suggestions that the general population’s widespread exposure to endocrine disrupting chemicals (EDCs) could be damaging human health. One argument is that the increases are roughly linked in time with the increased use and release of industrial chemicals into the environment. More...

4.3.2 Breast Cancer: Numerous studies have examined whether environmental EDCs, particularly organochlorine contaminants such as DDT and PCBs, may increase breast cancer risk in women, but the current scientific evidence does not support such a conclusion. All the studies have the same weakness in that they measured current EDC levels in women both with and without breast cancer, but they had no data on exposure during other potentially important periods in their lives, such as while they were in the womb, or during childhood and adolescence. During the mid-twentieth century, organochlorine contaminants were more widespread, making the absence of this early exposure information a major problem. More...

4.3.3 Endometrial Cancer: There are very few studies on endometrial cancer, which is cancer of the lining of the womb, and exposure to EDCs. Although exposure to oestrogen is known to increase the risk of this cancer, the number of women developing endometrial cancer is not increasing. The limited experimental and human studies available on this subject fail to draw a link between EDCs and endometrial cancer. More...

4.3.4 Testicular Cancer: Cancer of the testis is the most common cancer in young men. A number of countries have reported increases of this form of cancer, but with considerably varying rates. The rate started rising around 1910 in the Nordic countries – even earlier in England and Wales – which means it cannot be attributed solely to chemicals introduced in the mid- or late twentieth century. Some evidence suggests that male sex organ abnormalities (see 4.1.) may be linked to testicular cancer, both because they have a similar geographical distribution and because they may have a common origin if sex hormone levels are disturbed during early development. However, no studies have examined the relationship between testicular cancer and EDC exposure during critical periods of development. More...

4.3.5 Prostate Cancer: Prostate cancer occurs mainly in older men and is the most common male cancer. Much of the increase in prostate cancer is due to improved diagnosis. It is known that male sex hormones cause growth of prostate cancers and oestrogens reduce the size of prostate cancers. Exposure to certain pesticides and organochlorines has been linked to increases in the incidence of prostate cancer in a few limited studies. Other studies have found no association between EDC exposure and this form of cancer. More...

4.3.6 Thyroid Cancer: It is known from experimental animal studies that some chemicals, such as certain pesticides, can disturb the part of the brain that controls thyroid hormone release, or can increase the destruction rate of thyroid hormones in the liver, thereby causing thyroid tumours. Yet so far no relationship between exposure to EDCs and thyroid cancer in humans has been shown. More...

4.4 What other factors must be considered regarding human health?

Three kinds of evidence have to be considered in reaching tentative conclusions about EDCs and human health at this point in time:

  • knowledge about hormones and the endocrine system: overall, the biological plausibility of possible damage to certain human functions from exposure to EDCs seems strong, particularly for reproduction and development;
  • evidence from other species: adverse effects found in wildlife and laboratory animals exposed to EDCs support concerns about possible similar effects in humans;
  • evidence from humans: changes in certain human health trends are also worrying enough to make this area a high research priority.

Both the possible roles of EDCs and non-EDC mechanisms need to be explored. Above all, the links between human exposure to low environmental levels of EDCs and health effects needs to be investigated. More...


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