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Changing Male Fertility

Male fertility is changing, and men are becoming less fertile and the average man produces less semen and fewer sperm per ml with each passing decade. Semen samples from men born in 1925 had about 4x the number of sperm compared to samples taken in 2005. ii When the size of semen samples is compared in the last century, there’s a clear trend: i

    • 1940 sperm concentrations were 113 million/ml
    • 1990 sperm concentrations were 66 million/ml
    • 2019 sperm concentrations were 45 million/ml

Studies suggest that 15 to 20% of young men now have sperm counts below 20 million/ml. There’s evidence that exposure to pollutants potentially reduces male fertility at two points in a man’s life:

  1. In the womb
  2. Adulthood

In the womb

There’s a crucial stage (between 6 weeks and 6 months) when a baby’s sex hormones become active, and nearly all sexual development occurs. All babies start off with an incomplete ‘female’ model, and in boys, this needs to change to a ‘male’ model. Differences in the DNA on the ‘Y’ chromosome trigger the release of male androgen” hormones. The androgens act on the undefined sex organs and alter their structure and function to the male model. After this development stage, the androgens “shut down” until the boy gets bigger and reaches puberty.
A man’s main sex organs are his testes, and these need structures that make sperm and more androgens (especially testosterone). If these structures don’t fully form in the womb, it affects how sex organs function in adulthood. There’s little response to the androgens released in the womb in extreme cases, causing androgen insensitivity syndrome.

The testes

The testes contain crucial cells for male sexuality:
  • Sertoli cells are the structures that form sperm, and each Sertoli cell can only grow a limited number of sperm, which determines how many sperm a man can produce
  • Leydig cells produce testosteronethe most important of the male hormones

1: Basal lamina, 2-6: Spermatogonia, 3: Spermatocytes and spermatids, 7: Sertoli cell, 8: tight junction iii

The DNA on the ‘Y’ chromosomes triggers the release of hormones that stimulate the development of the testes. Because the baby’s blood supply ultimately comes from the mother, the hormones in her blood will affect the baby. If her female sex hormone levels are abnormal, they can affect how her baby boy’s sex cells develop. This can have long-term consequences for his future fertility.

When a mother’s blood has high levels of estrogen-like substances or other toxins, they can counter-balance the “burst” of androgens. Without the usual level of stimulation, there is less growth and development in the baby’s Sertoli and Leydig cells. There are parallels here with how women’s egg numbers are set in the womb at this stage.

21st-century living brings with it environmental exposure to a wide range of hormones and hormone-like substances. This includes man-made (rather than plant-based) estrogens, which don’t break down easily but build up in the body. They’re a major issue for male embryos as many women unknowingly carry chemicals that affect the sexual development of their unborn children. iv


Adult men are exposed to Endocrine Disrupting Chemicals (EDC) in substances like medications, DDT, PCBs, inks, paints, plastics, antibiotics, glues, drinks and foods. These directly affect the quantity and quality of the sperm currently growing in his testes. Lifestyle choices such as smoking (especially marijuana) and drinking alcohol also reduce sperm counts and cause high levels of abnormal sperm.
Fortunately, stopping exposure to these substances usually reverses the effect on sperm once the chemicals leave the body. For example, sperm counts are much better 6-12 months after stopping smoking. v The male population is generally getting heavier, and many couples are starting (or extending) their family later in life. These both impact a man’s fertility as age and weight reduce sperm quality.v
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