Diabetes and Endocrinology Topic Homepage

Cancer can develop within the thyroid gland. Although it is a seldom cancer with 1% of all malignancies registered in UK, it constitutes more than 90% of the cancers of the endocrine glands.³ Thyroid cancer is more common in women than in men, with an incidence around 2.5 times more in the UK in 2010 (1900 new cases for women versus 700 for men).⁴ There are 4 main types of thyroid cancer: papillary thyroid cancer (60% of the thyroid cancers), follicular thyroid cancer (15%), medullary thyroid cancer (5-10%) and anaplastic thyroid cancer (5%).²

The incidence of many endocrine-related diseases has been increasing in humans (breast cancer, prostate cancer, testicular cancer, obesity, diabetes and infertility) for the last 50 years.^5,6
With 347 million people worldwide having diabetes, this condition constitutes the main endocrine disease. Of this number 10% are suffering from type 1 and 90% from type 2.⁷ Type 2 diabetes is even diagnosed in children and adolescents.¹

Moreover, although preventable by diet and physical activity, overweight and obesity have increased twice since 1980 and now represent the 5th leading risk for global death.⁸ According to WHO, overweight is defined by a body mass index (BMI) ≥ 25 kg/m² and obese by a BMI ≥30 kg/m².
In 2008, 1.4 billion adults were overweight and 500 million were obese.
In 2011, more than 40 million children under 5 years old were overweight. WHO estimates that “44% of the diabetes burden, 23% of the ischaemic heart disease burden and 7 to 41% of certain cancers burden are attributable to overweight and obesity”.⁸

Additionally, some endocrine-related effects in wildlife populations have been observed and some chemicals with endocrine disrupting properties linked to disease outcomes have been identified in the laboratory.^1,6

Those chemicals are called “Endocrine Disruptors Chemicals” (EDCs). The International Programme on Chemical Safety (IPCS) is a joint programme of WHO, United Nations Environment Programme (UNEP) and the International Labour Organization, giving the following definitions: “An endocrine disruptor is an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub) populations” and “A potential endocrine disruptor is an exogenous substance or mixture that possesses properties that might be expressed to lead to endocrine disruption in an intact organism or its progeny, or (sub) populations”.⁶

The endocrine disruptors can be natural, like the phytoesrogens (e.g. isoflavonoids in soya beans) or synthetic like pesticides (e.g. dichlorodiphenyl trichloroethane (DDT)). Exposure can be by ingestion, inhalation, dermal absorption, transplacental or by breast milk.¹

The endocrine disruptors can act: directly on the hormone receptors, alter the synthesis and the metabolism of the hormones or of the hormone receptors or possibly change the cell sensitivity to a specific hormone.^1,6
They can act on nuclear receptors, non-nuclear steroid hormone receptors, non-steroid receptors, orphan receptors, enzymatic pathways involved in steroid biosynthesis and/or metabolism and they can have simultaneous actions on different receptors.^5,6

The severity of the effects related to the endocrine disruption depends on different factors, notably age. As fetuses and infants are in development, they are more sensitive.^1,5,6
The effects of the endocrine disruptors may appear later as there is latency of exposure and some synergistic effects are possible, even when the EDCs are combined at low doses that individually do not produce observable effects.^1,6 These molecules are lipophiles and accumulate in adipocytes.^1,5,6 They also produce non-linear dose responses and show tissue specific effects.⁶

The effects of EDCs can be various. Precocious puberty has been associated to exposure to DDT, Polychlorinated Biphenyls (PCBs) and phtalates (used as a plasticizers in polyvinyl chloride (PVC), cosmetics and fragrance).¹
The thyroid gland which regulates the brain development can be disrupted, by, for example: PCBs, detergent derivative monylphenol, plasticiser dibutylphtalate, plastic triclosan, polybromintaed phenyls and some UV-filters.¹

The main messages given by WHO and UNEP are that the EDCs are everywhere and their numbers are increasing. People are exposed to mixtures occurring at early life stages. All sources of EDCs aren’t known.⁶

Currently, around 800 chemicals are considered as EDCs or potential EDCs but just a few of them have been studied to assess their impact.⁶ According to WHO, it is important that the physicians “report cases that can be related to environmental exposure as they may be sentinel cases”.¹

1. World Health Organization. Children’s Health and the Environment: Endocrine Disorders and Children. October 2011. Available at: http://www.who.int/ceh/capacity/endocrine.pdf, accessed the 11th of March 2013.
2. Beers M.H. et al. The Merck manual of medical information. Merck research laboratories. Second home edition. 2003 ; 937-975.
3. Vanderpump M.P.J. The epidemiology of thyroid diseases. Br Med Bull (2011) 99 (1): 39-51.
4. Cancer Research UK. Thyroid Cancer key facts. Available at: http://www.cancerresearchuk.org/cancer-info/cancerstats/keyfacts/thyroid-cancer/ accessed the 11th of March 2013.
5. De Coster S. et al. Endocrine-Disrupting Chemicals: Associated Disorders and Mechanisms of Action. J Environ Public Health. 2012; 2012: 713696.
6. World Health Organization / United Nations Environment Programme. State of the Science of Endocrine Disrupting Chemicals – 2012. Available at: http://www.who.int/iris/bitstream/10665/78101/1/9789241505031_eng.pdf, accessed the 11th of March 2013.
7. World Health Organization. Diabetes - Fact Sheet N° 312, March 2013. Available at: http://www.who.int/mediacentre/factsheets/fs312/en/, accessed the 11th of March 2013.
8. World Health Organization. Obesity and overweight - Fact Sheet N° 311, March 2013. Available at: http://www.who.int/mediacentre/factsheets/fs311/en/index.html, accessed the 11th of March 2013.