Health consequences of obesity

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Title of Part 1

Endocrine Changes in Obesity

Endocrine Changes

It is well documented that obesity is associated with changes in the normal endocrine profile. Many studies have focused particularly on the alterations in the sex steroid profile of obese individuals. This section of the article will briefly discuss the types of changes observed and their consequences on the health of the individual.

Oestrogens

Oestrogens are synthesized by aromatization of circulating testosterones. This conversion reaction is catalysed by the enzyme aromatase (Ali,) which is expressed at many sites throughout the body, including adipose tissue. Therefore, an increase in adipose tissue mass, results in a greater capacity for aromatization, and oestrogen levels rise.

The effects of obesity on oestrogen concentrations are augmented in postmenopausal women. In premenopausal, non-pregnant women, the principal site at which this takes place is the ovaries (Simpsom 2000) and so the contribution of adipose tissue to overall oestrogen synthesis is minor. However, after the menopause, adipose tissue becomes the main source of oestrogens (Simpson.)

Androgens

The increased capacity for aromatization results in hypoandrogenism in males, as a higher proportion of circulating testosterone is converted to oestrogen (Hammoud et al.) Other factors contributing to the decrease in circulating testoerone include insulin resistance and the suppression of the hypothalamic pituitary testicular axis (Hammoud.)

Most studies in premenopausal women have demonstrated that the concentration of free testosterone in the circulation increases with body weight. It has been proposed that the relationship between body weight and androgens is mediated by insulin and IGF-1, which are both increased in obese subjects.

Furthermore, as is the case for oestrogen, adipose tissue is an important site of peripheral testosterone production, due to local expression of 17 beta hydroxysteroid dehydroenase. Therefore there is a positive association between adipose tissue mass and androgen concentration.

SHBG

Sex steroids are highly lipophilic and are therefore carried in the circulation bound to proteins – sex hormone binding globulins (SHBG.) It is well documented that obesity results in a decreased concentration of SHBG. This is thought to be associated with the rise in insulin levels associated with obesity, as insulin inhibits hepatic synthesis of SHBG. The decreased concentration of binding protein results in an increase in the free fraction of sex steroids. (2)

Obesity and Cancer

It is estimated that 10% of all cancer deaths among non-smokers are related to obesity. Many hypotheses have been proposed to explain this, the most convincing of which is that alterations in endogenous hormone metabolism mediate the effects of obesity on cancer risk Kalle et al. This in part thought to be true due to the fact that sex steroids regulate the balance between cell proliferation, differentiation and apoptosis. 3

Many types of cancer are more prevalent in obese subjects, the most widely studied of which are breast and endometrial cancer. It has been observed that these types of cancer are associated with an increase in oestrogen concentration, decrease in plasma SHBG and an increase in androgen levels. (3, 2) These observations have led to the establishment of the unopposed oestrogen hypothesis. This hypothesis suggests that risk of cancer is due to increased exposure to oestrogen, which is unopposed by progestagens. This results in increased mitotic activity of cells. (Key et al) Increased mitosis, increases the risk of mutation accumulation, and thus the development of cancer.

Infertility

Obesity is thought to account for around 6% of primary infertiliy. (1)

Women

Many studies have observed increased number of atretic follicles in obese women. This reflects the increased risk of anovulatory infertility in obese women. * The anovulation is mainly due to hyperandrogenism. High androgen levels cause increased apoptosis of the granulosa cells, damage to the endometrium and developing oocytes. Excess oestrogen also contributes to infertility. This is partly due to increased negative feedback causing decreased gonadotrophin secretion (1,

PCOS

There is a well established link between PCOS and obesity. This syndrome is characterized by anovulatory infertility, obesity, hirsutism, multiple ovarian cysts and insulin resistance. ? It is unkown whether PCOS is a cause or effect of obesity (*.)

Men

Obese men generally express “hyperoestrogenic hypogonadotropic hypogonadism.” (hAMMOUD, one of other first ref) Essentially the high oestrogen levels, combined with low testosterone levels result in subfertility.

Many studies have reported a negative association between spermatogenesis and increasing BMI. The mechanism mediating this association is yet to be identified. However, it has been suggested that the gerneral hypoandrogenism observed in obese males, may reflect a reduced concentration of testosterone within the testes, which would cause a reduction in sperm count. Furthermore, the observed hyperoestrogenism causes inappropriate suppression of the hypothalamic-pituitary-gonadal axis, resulting in reduced spermatogenesis. The effects of obesity on spermatogenesis is thought to be qualitiative as well as quantitative. For example, .Ghanayem et al . . showed reduced sperm motlity and hyperactivated progression.

Obesity has also been associated with erectile dysfunction (hammoud, first). Feldman et al found that 79% of men suffering erectile dysunction were overweight or obese. Although erectile dysfunction is hought to be in part a result of hypoandrogenism, the main cause is thought to be related to endothelial dysfunction and disruption of the nitric oxide pathway.

In summary, alterations in sex steroid profiles as a result of obesity have many adverse effects on health. The most well documented health consequences are cancer and infertility.

Title of Subpart 2

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Psychosocial Consequences of Obesity

The relationship between obesity and mental health has been the subject of continuous debate over the past 30 years and remains a topic of extensive deliberation.1 Early studies exploring the relationship were consistent with the “jolly fat” hypothesis, suggesting that obesity confers a protective role against anxiety and depressive disorders;1 however, the weight of more recent studies contradict the “jolly fat” hypothesis and suggest that the increasing global prevalence of both depression and obesity are functionally linked.2,3 The underlying mechanisms and direction of this link remain largely unknown,3 although recent research has indicated that gender, obesity severity, comorbid physical illness, stress and abdominal fat distribution are important mediating risk factors for the development of an obesity-mental disorder link.1,2,4,5, These newly discovered mediators give rise to new hypotheses, involving over-activity of the hypothalamic-pituitary-adrenocortical axis,1,2 side-effects of medication for depression, and the social stigmatization of obesity.2

A recent nationally representative Canadian study, whose methodology controlled for sociodemographic factors and comorbid physical health problems, found significant positive relationships between obesity and an array of lifetime psychiatric disorders and past-year mood and anxiety disorders.2 These conclusions are consistent with current literature.6,5,7,8 Further subgroup analyses revealed that obese women had a greater susceptibility to specific mental disorders compared to men, including depression, mania, panic attacks, panic disorder, social phobia and agoraphobia (with and without panic).3 These findings are consistent with previous research, and thus reinforce the notion that obese women have an enhanced vulnerability towards mental disorders.2,4,5,7,9 This result may be explained in terms of the increased consciousness amongst women to conform to a socially desirable image and weight.3 The study also positively linked obesity to suicidal behaviours and negatively linked obesity with past-year drug dependence3; both these findings are supportive of existing literature.6,7,10 Mather et al. (2009) suggest that the former may be attributed to the social stigmatization attached to obesity, inducing feelings of decreased self-worth and decreased self-esteem that fuel suicidal thoughts; and the latter due to protective effects of obesity, arising through food and addictive drugs competing for the same reward sites in the brain.3,11 At face value, this data appears convincing, however, it is important to note that some studies fail to identify mental disorders as a psychosocial consequence of obesity.12,13 Similarly, whilst much research is indicative of sex differences between obesity and mental disorders,1,5 this is not a unanimous conclusion.6,7,14 In addition, some research only identifies associations amongst the severely obese, who illustrate a BMI of >35kg/m2.5 These variable conclusions may in part be attributed to methodological differences between studies.5

1 Rivenes, A.C., Harvey, S.B., and Mykltun, A. (2009). The relationship between abdominal fat, obesity, and common mental disorders: Results from the HUNT Study. Journal of Psychosomatic Research, 66: 269-275.

2 Stunkard, A.J., Faith, M.S. and Allison, K.C. (2003). Depression and Obesity. Society of Biological Psychiatry, 54: 330-337. 3 Mather, A.A., Brian, J.C., Enns, M.W. and Sareen, J. (2009). Association of obesity with psychiatric disorders and suicidal behaviours in a nationally representative sample. Journal of Psychosomatic Research, 66: 277-285. 4 Simon, G.E., Ludman, E.J., Linde, J.A., Operskalski, B.H., Ichikawa, L., Rohde, P., Finch, E.A. and Jeffery, R.W. (2008). Association between obesity and depression in middle-aged women. Gen Hosp Psychiatry, 30(1): 32-39. 5 Scott, K.M., Bruffaerts, R., Simon, G.E., Alonso, J., Angermeyer, M., de Girolamo, G., Demyttenaere, K., Gasquet, I., Haro, J.M., Karam, E., Kessler, R.C., Levinson, D., Mora, M.E.M., Browne, M.O., Ormel, J.H., Villa, J.P., Uda, H. and von Korff, M. (2008). Obesity and Mental Disorders in the General Population: Results from the World Mental Health Surveys. Int J Obes, 32(1):192-200. 6 Simon, G.E., Von Korff, M., Saunders, K., Miglioretti, D.L., Crane, P.K., van Belle, G. and Kessler, R.C. (2006). Association Between Obesity and Psychiatric Disorders in the US Adult Population. Arch Gen Psychiatry, 63: 824-830. 7 Carpenter, K.M., Hasin, D.S., Allison, D.B. and Faith, M.S. (2000) Relationships between obesity and DSM-IV major depressive disorder, suicide ideation, and suicide attempts: results from a general population study. Am J Public Health, 90:251–257. 8 Onyike, C.U., Crum R.M. and Lee H.B. (2003). Is obesity associated with major depression? Results from the third National Health and Nutrition Examination Survey. Am J Epidemiol, 158:1139–1147. 9 Scott, K.M., Oakley Browne, M.A., McGee, M.A. and Wells, J.E. (2006). Mental-physical comorbidity in Te Rau Hinengaro: the New Zealand Mental Health Survey (NZMHS). Australian and New Zealand Journal of Psychiatry, 40:882–888. 10 Dong, C., Li, W.D. and Li, D. (2006). Extreme obesity is associated with suicide attempts: results from a family study. Int J Obes, 30: 388-390. 11 Kleiner, K.D., Gold, M.S., Frost-Pineda, K. (2004). Body mass index and alcohol use. J Addict Dis, 23:105-118. 12 Hasler, G., Pine, D.S. and Gamma, A. (2004). The associations between psychopathology and being overweight: A 20-year prospective study. Psychol Med, 34:1047–157. 13 Faith, M.S., Matz, P.E. and Jorge, M.A. (2002). Obesity-depression associations in the population. J Psychosom Res, 53:935–942. 14 Onyike, C.U., Crum, R.M., Lee, H.B., Lyketsos, C.G. and Eaton, W.W. (2003). Is obesity associated with major depression? Results from the Third National Health and Nutrition Examination Survey. American Journal of Epidemiology. 158(12):1139–1147. Rachael White 15:09, 23 October 2009 (UTC)

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Title of Part 3

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