Hormones

Healthy young men restricted to five hours of sleep for one week. Testosterone dropped 10 to 15%. Published in JAMA.

This is because testosterone is synthesised primarily during REM sleep in the early morning hours. Equivalent to 10 to 15 years of hormonal ageing in seven days.

Each ejaculation depletes 0.5 to 1.0 milligrams of zinc, plus selenium, magnesium, calcium and protein. A man ejaculating daily loses 15 to 30 milligrams of zinc per month.

Testosterone levels show a documented peak at approximately 145% of baseline around day seven of abstinence and the nutrients lost through ejaculation are precisely those required for testosterone synthesis.

A 2017 meta-analysis of 42,935 men from 185 studies found sperm concentration declined 52.4% and total sperm count declined 59.3% between 1973 and 2011 in Western countries.

The 2023 update extended this to 2018 and found the decline has accelerated. Post-2000 data shows a decline rate of 2.64% per year, more than double the earlier trend.

The updated analysis also confirmed the decline is no longer limited to Western nations. South America, Asia and Africa now show the same trajectory.

Shanna Swan, the lead epidemiologist on this data, projected that at current rates sperm counts could approach zero by 2045, a trajectory that has shown no sign of reversing.

Pilz et al.'s 2011 randomised controlled trial in Hormone and Metabolic Research assigned 165 overweight men with serum 25(OH)D below 50 nmol/L to either 3,332 IU vitamin D3 daily or placebo for twelve months. The vitamin D group showed a 25.2 per cent increase in total testosterone (from 10.7 to 13.4 nmol/L), a 19.3 per cent increase in bioactive testosterone and a 20.3 per cent increase in free testosterone. The placebo group showed no significant change in any testosterone measure.

This is because vitamin D receptors are expressed in Leydig cells, the primary testosterone-producing cells in the testes. Vitamin D modulates the expression of aromatase (which converts testosterone to oestrogen) and 17-beta-hydroxysteroid dehydrogenase (which catalyses the final step of testosterone synthesis). Wehr et al. (2010) found a significant positive correlation between 25(OH)D levels and total testosterone in a cross-sectional study of 2,299 men, with testosterone nadir coinciding with the winter vitamin D trough.

An estimated one in five UK adults has serum 25(OH)D below 25 nmol/L (the threshold for deficiency), rising to approximately one in three during winter months. Public Health England recommends 400 IU of vitamin D daily during autumn and winter, a dose that Pilz et al. found insufficient to achieve the serum levels associated with testosterone optimisation. The trial used 3,332 IU daily, more than eight times the government recommendation. The trial answers what dose restores deficient men. It does not answer where the dose should come from. Fifteen to twenty minutes of full-body summer sun produces 10,000 to 20,000 IU per session without bypassing the skin's self-regulation; fermented cod liver oil delivers 1,000 to 2,000 IU per teaspoon in the same fat-soluble matrix Weston Price documented across the dental health record. Supplementation is what the indoor lifestyle has made necessary. Sunlight and traditional fat-soluble foods are what the body was designed to use.

The Massachusetts Male Aging Study tracked testosterone levels across three cohorts between 1987 and 2004. In men aged 65 to 69, mean total testosterone fell from 503 ng/dL in 1988 to 423 ng/dL in 2003.

The decline persisted after adjusting for age, BMI, obesity, smoking, alcohol, medications and chronic illness. Within-person decline averaged 1.6% per year.

Sex hormone binding globulin rose 1.2% per year across all cohorts, further reducing bioavailable testosterone even where total levels appeared stable.

The decline is generational, not individual. Men born later start lower and fall faster. The inputs changed. The biology followed.

Bisphenol A is detectable in over 90% of urine samples in NHANES biomonitoring data. Phthalates are found in 75% of the tested population and associated with an 8% reduction in testosterone per log unit increase in exposure.

Tyrone Hayes demonstrated that atrazine, the most widely used herbicide in the United States, induces hermaphroditism in frogs at 0.1 parts per billion and complete sex reversal in 10% of exposed animals at 2.5 ppb. This is below the EPA drinking water standard of 3 ppb. The EU banned atrazine in 2004.

PFAS compounds are detectable in 97 to 99% of Americans. These chemicals do not break down in the environment and accumulate in tissue over a lifetime.

The UK total fertility rate fell to 1.44 in 2023, the lowest since records began. Multiple exposures interact. No single chemical tells the full story.

Dettenborn et al.'s 2010 study in Psychoneuroendocrinology measured hair cortisol concentrations (reflecting average cortisol exposure over three to six months) in long-term unemployed individuals versus employed controls. The unemployed group showed cortisol levels 22 per cent higher than controls. Stalder et al.'s 2017 meta-analysis of 124 studies validated hair cortisol as a biomarker of chronic stress and found consistent elevations associated with unemployment, shift work, caregiving burden and low socioeconomic status.

This is because chronic cortisol elevation suppresses testosterone production (via GnRH inhibition at the hypothalamus), impairs insulin sensitivity (via hepatic gluconeogenesis upregulation), increases visceral fat deposition (via cortisol-mediated lipogenesis in abdominal adipocytes) and suppresses immune function (via lymphocyte apoptosis). The modern combination of sleep deprivation, sedentary indoor work, processed food intake, financial stress and social media comparison creates a chronic cortisol environment without historical precedent. Sapolsky (2004) documented that chronically stressed baboons showed the same pattern: elevated cortisol, reduced testosterone, increased visceral fat and impaired immune function.

The human endocrine system evolved for acute stress responses lasting minutes to hours, with cortisol returning to baseline through negative feedback at the hypothalamus and pituitary. Chronic low-grade stress maintains cortisol above baseline without triggering the acute stress response, evading the feedback loop. The downstream effects, low testosterone, insulin resistance, visceral obesity, immunosuppression, are the defining metabolic conditions of the modern era. Each is treated as a separate disease by separate specialists, rather than recognised as downstream consequences of a single upstream hormonal disruption.

Pugeat et al.'s 1991 study in the Journal of Clinical Endocrinology and Metabolism demonstrated that insulin directly suppresses hepatic production of sex hormone-binding globulin (SHBG), the glycoprotein that binds and regulates the bioavailability of testosterone and oestrogen. In insulin-resistant individuals, SHBG levels are approximately 40 per cent lower than in insulin-sensitive controls. Low SHBG in men is associated with lower total testosterone and higher bioavailable oestrogen, while in women it drives the hyperandrogenism characteristic of polycystic ovary syndrome (PCOS).

This is because insulin acts on hepatocyte insulin receptors to suppress SHBG gene transcription via the HNF-4alpha transcription factor pathway. The effect is dose-dependent: higher circulating insulin produces lower SHBG. Since approximately 30 per cent of UK adults meet criteria for insulin resistance (defined by HOMA-IR above 2.5), this mechanism represents a population-level hormonal disruption driven by metabolic status. Ding et al. (2006) found that each one-unit increase in HOMA-IR was associated with a 10 per cent decrease in SHBG in a study of 1,462 adults.

The clinical implication is that insulin resistance does not merely affect blood sugar. It rewires the hormonal environment. In men, insulin-driven SHBG suppression contributes to the "male hypogonadism epidemic" now documented across Western populations. In women, it is the primary driver of PCOS, which affects approximately one in ten women of reproductive age. Treating the insulin resistance (through diet, exercise or fasting) raises SHBG, normalises the androgen-to-oestrogen ratio and in many cases resolves PCOS symptoms without pharmaceutical intervention.

Anogenital distance is a sensitive biomarker of prenatal androgen exposure; reduced AGD in males indicates feminisation of the genital development programme. Boys born to mothers in the highest phthalate quartile showed significantly shorter AGD than those in the lowest.

Phthalates inhibit foetal testicular testosterone synthesis during the critical masculinisation programming window. This same mechanism underlies the "phthalate syndrome" in rodent studies, which includes cryptorchidism, hypospadias and impaired sperm production.

Phthalates are present in PVC products, cosmetics, food packaging and medical tubing. Prenatal exposure through diet and personal care products is essentially unavoidable under current regulatory conditions.

Calafat et al.'s 2008 analysis of 2,517 participants in the CDC's National Health and Nutrition Examination Survey (NHANES) found detectable bisphenol A (BPA) in the urine of 93 per cent of participants aged six and older. Geometric mean concentration was 2.6 µg/L. Children aged six to eleven had significantly higher concentrations than adults, consistent with higher food intake relative to body weight and greater hand-to-mouth behaviour. BPA was ubiquitous across all demographic groups, income levels and geographic regions.

This is because BPA is used in polycarbonate plastics, epoxy can linings, thermal receipt paper and dental sealants. It leaches into food and drink, particularly when heated. BPA binds to oestrogen receptors alpha and beta with an affinity approximately 10,000 times weaker than endogenous oestradiol, but at the concentrations found in human tissue it produces measurable oestrogenic effects. Vom Saal and Hughes (2005) documented in Environmental Health Perspectives that BPA at concentrations below the EPA reference dose produced significant effects on prostate weight, breast tissue and reproductive development in animal models.

The European Food Safety Authority reduced the tolerable daily intake of BPA by 20,000-fold in 2023, from 4 µg/kg body weight/day to 0.2 ng/kg body weight/day, acknowledging that previous safety assessments had underestimated the risk. This new limit means the general European population is exposed at levels 3 to 5 times above the revised safe threshold. "BPA-free" products frequently substitute bisphenol S (BPS) or bisphenol F (BPF), which Rochester and Bolden (2015) showed have comparable oestrogenic potency to BPA in vitro.

The CDC National Health and Nutrition Examination Survey (NHANES, 2003-2004) detected bisphenol A (BPA) in the urine of 93% of the US population aged six years and older. BPA is a synthetic xenoestrogen used in polycarbonate plastics, epoxy can linings, thermal receipt paper and dental sealants. It binds to oestrogen receptors (ERα and ERβ) at concentrations as low as 0.23 parts per trillion, mimicking endogenous oestradiol and disrupting normal hormonal signalling.

This is because BPA leaches from containers at rates that increase dramatically with heat exposure. Vandenberg et al. (2007, Reproductive Toxicology) demonstrated that "BPA-free" replacements (BPS, BPF) show equivalent or greater oestrogenic activity than BPA itself, meaning the substitution has not resolved the exposure problem. BPA exposure has been associated in human epidemiological studies with decreased sperm quality, early puberty in girls, polycystic ovary syndrome, obesity, type 2 diabetes and increased breast and prostate cancer risk.

The current US FDA reference dose for BPA (50 μg/kg/day) was established in the 1980s based on studies funded by the chemical industry. Independent academic research, reviewed by vom Saal et al. (2007, Reproductive Toxicology), found adverse effects at doses 1,000-25,000 times lower than the regulatory threshold. The regulatory framework for endocrine-disrupting chemicals does not account for non-monotonic dose-response curves (where low doses can produce stronger effects than high doses), a fundamental characteristic of hormonal signalling.

Kruger et al. (2003, Journal of Endocrinology) measured plasma prolactin in ten healthy men before, during and after orgasm achieved through masturbation. Prolactin levels increased by approximately 400 per cent within five minutes of orgasm and remained elevated for sixty minutes. A subsequent study by Brody and Kruger (2006, Biological Psychology) found that prolactin release after penile-vaginal intercourse was 400 per cent greater than after masturbation, suggesting distinct neuroendocrine responses to different sexual contexts.

This is because prolactin release from the anterior pituitary is tonically inhibited by dopaminergic neurons from the tuberoinfundibular pathway. Orgasm triggers a massive dopamine surge in the nucleus accumbens, followed by an equally dramatic dopamine withdrawal, during which prolactin inhibition is released. Elevated prolactin then suppresses further dopamine release through negative feedback, creating the refractory period. This prolactin-dopamine seesaw is the mechanism behind post-orgasmic lethargy, reduced motivation and decreased sexual desire.

The implications for frequent ejaculation are straightforward: each episode triggers a prolactin surge that temporarily suppresses dopaminergic tone. In men ejaculating daily or multiple times daily (facilitated by internet pornography), the cumulative effect is chronic prolactin elevation and chronic dopamine suppression. Cabergoline, a dopamine agonist that suppresses prolactin, is used clinically to eliminate the refractory period, confirming that prolactin is the causal mediator of post-ejaculatory suppression.