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Obesity and fertility - it would be helpful to elaborate on the link between obesity and fertility in males, using evidence and peer reviewed articles, also would be useful to lay out the information in more of a digestible way so that it is meaningful to the general public who access this Wikipedia article

Epidemiology: Added epidemiology section to provide broad overview of epidemiology of obesity and overweight, moved epidemiology bit touching on women with PCOS to "Women" section underneath sub-heading PCOS

(WHO website - https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight )

Obesity and overweight are serious risks that are linked to a greater number of deaths worldwide compared to underweight. On a global scale, there are more people who are obese than underweight. This finding occurs in every region worldwide with the exception of parts of sub-Saharan Africa and Asia.

Previously, obesity and overweight were considered problems that were nearly exclusive to high-income countries; however, the prevalence of these health problems is now rising in low- and middle- income countries. Furthermore, obesity and overweight are health issues which are more prevalent in urban areas compared to rural areas.

Since 1975, obesity rates have tripled worldwide.

As of 2016, 1.9 billion adults (aged 18 years or older) were classified as being overweight, and within these adults, 650 million were classified as obese. This translates to 39% of adults (39% of men and 40% of women) being overweight and 13% of the adult population worldwide (11% of men and 15% of women) being obese in 2016.

An estimated 38.2 million children under 5 years of age were either overweight or obese as of 2019. In Africa, the number of overweight children under 5 years of age has increased by 24% percent since 2000. Almost half of the children under 5 who were overweight or obese in 2019 lived in Asia.

In 2016, over 340 million children and adolescents from ages 5-19 were overweight or obese. More 124 million children and adolescents aged 5-19 (6% of girls and 8% of boys) were obese in 2016, as compared to 1975 where obesity affected just under 1% of children and adolescents in this age range. The prevalence of obesity and overweight among children and adolescents within the ages of 5-19 years has significantly risen from 4% in 1975 to just above 18% in 2016. This marked increase in the rate among children has occurred similarly among both boys and girls, reflected in the 2016 statistic where 18% of girls and 19% of boys were overweight.

Men - Obesity and fertility

Numerous studies show the association between obesity in men and infertility. In the developed world, the temporal trend for the reduction in sperm parameters (sperm count, motility, morphology, volume, fructose level, and pH) reflects the increasing prevalence of obesity.

The reproductive potential of obese men can be attributed to changes in hormone levels which regulate spermatogenesis, increased temperatures in the testicles, an accumulation of environmental toxins in adipose tissue, and increased levels of oxidative stress as well as a higher incidence of erectile dysfunction.

Changes in Hormonal levels regulating spermatogenesis - referenced briefly in wikipedia article

In males, the accumulation of fatty tissue is linked to a decrease in free testosterone in the serum, which has been proposed to lead to low sperm count.

Increased temperatures in testicles - not addressed in article

Obesity may potentially contribute to altered production and parameters of sperm due to an increase of heat within the testicle region. Gonadal heat results from an increase in fat or adipose tissue in the scrotum, also called increased adiposity. Spermatogenesis is a process which is extremely heat sensitive. The optimal temperature for sperm production in humans ranges between 34–35°C. Sperm cells could undergo harm due to elevated temperatures within the scrotum due to a build up of fat tissue. The damages that heat could pose on sperm production are associated with a reduction in sperm motility, an increase in sperm DNA fragmentation, and increased sperm oxidative stress.

Environmental toxins - not addressed in article

Research clearly demonstrates that metals and chemicals which exist in air, water, food, and health and beauty products are associated with a reduction in fertility in many ways. These toxicants cause infertility in males via decreasing sperm count and function. Among men who presented to a fertility clinic, it was found that those who consumed fruits and vegetables with high levels of pesticide residues had a lower total sperm count as well as a lower percentage of morphologically normal sperm. Moreover, a United States study which enrolled 501 participants found a significant association between infertility and blood lead levels in men. Tobacco use is another common cause of toxin exposure in the air. Using tobacco in the form of cigarette smoking has shown to decrease male fertility, resulting in a decrease in sperm parameters such as sperm density, total sperm count, and number of motile sperm.