Obese people are the most likely to suffer from short stature, but there is also significant evidence linking obesity to infertility. An international research team led by Dr. Raquel David at the University of Granada has now found an unexpected cause for this association: obesity-associated low sperm quality. The results of the study, published in Reproductive BioMedicine Online, show that men who were underweight or overweight were 29% less likely than normal weight men to father children with their partners after undergoing IVF treatment. This trend was seen across all body mass indexes (BMI), suggesting that it has biological origins rather than being simply caused by weight gain during adult life (or vice versa). The team concludes that "our data suggest that male obesity may have a previously unrecognized negative effect on male fertility." However, the authors caution that their findings are only significant in the minority of obese men who have low sperm quality. Obesity is considered to be one of the most important predictor for poor reproductive outcome. Obese couples are 2.4 times less likely to achieve a live birth rates among other factors. Most of studies on infertility in couples with an obese man are focused on ovulation issues, which could be caused by exogenous factors, such as hypothalamic or pituitary dysfunction or other metabolic diseases. The biological mechanisms that are related to the decreased fertility are not well understood. We know that obesity is associated with metabolic disorders, such as diabetes or hypertension. Obesity is also correlated with elevated levels of inflammatory markers, which might play a role in infertility. Several studies have shown an association between excess fat tissue and low sperm quality in men. Excess fat tissue is known to impair the endocrine function of the testis by affecting testosterone production within the Leydig cells of Sertoli cells. Proliferation of Leydig precursor cells declines in testes from obese diabetic men compared with matched obese control men, while these cells respond normally to stimulation by LH or other agents in vitro. Also, Sertoli cells are known to express many inflammatory factors. A recent study has shown that these cells produce cytokines in vitro, which can lead to inflammation in vivo. Obese men have more significant levels of some cytokines in testes, while some other cytokines are increased within adipose tissue. The inflammatory markers IL-4, IL-6 and TNF-α were elevated more significantly in obese men compared to normal weight controls after 6 months of dieting, suggesting higher levels of inflammation during reproductive development. Obesity is associated with higher levels of fat within testicular stromal cell cultures from infertile men after high fat feeding for 6 weeks. This is caused by increased uptake of fatty acids, which are used as an energy source. Whether this leads to infertility is not clear. Studies have also suggested that some fatty components are associated with poor semen quality. Adipocytes are known to secrete molecules that can reduce sperm motility and viability. Fatty lipid components of seminal plasma have been linked to reduced semen volume, sperm motility, sperm count and abnormal morphology. Furthermore, trans faradation studies show that seminal plasma reduces the progressive motility of spermatozoa in vitro by affecting their membranes. The excess fat tissue of obesity may also affect the function of Leydig cells directly by acting on cell receptors or altering hormone metabolism.
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