When a man in his 40s or 50s comes to me with unexplained fatigue, reduced libido, difficulty maintaining muscle despite regular training, accumulating abdominal fat despite a reasonable diet, and perhaps some difficulty with erections, the conversation rarely starts with sleep. It starts with testosterone levels, thyroid function, perhaps a referral to a urologist. Sleep apnoea tends not to come up until I ask specifically about snoring or bed partner reports, and often not even then, because many men with significant OSA do not snore loudly or their partners sleep separately.
What the evidence shows is that sleep apnoea is quietly generating exactly this cluster of symptoms through its effects on the hormonal and metabolic environment, night after night, for years before diagnosis.
Testosterone: The Sleep Connection
Testosterone production is not a constant process. It is pulsatile — meaning it happens in bursts — driven by the release of a signalling hormone called luteinising hormone (LH) from the pituitary gland (the small hormone control centre at the base of the brain). Those LH pulses are tightly linked to sleep, particularly to slow-wave (deep) sleep in the first half of the night. Men who get adequate deep sleep wake with higher testosterone levels than those who do not. Sleep apnoea disrupts deep sleep continuously and also adds direct suppression of the testes through nocturnal hypoxia: the Leydig cells that produce testosterone in the testes are sensitive to oxygen levels, and repeated oxygen drops impair their function.
Multiple meta-analyses — studies pooling results from many separate investigations — now confirm that men with OSA have significantly lower testosterone than men without it. Researchers express this using a measure called a standardised mean difference (SMD), which describes how far apart two groups are in statistical terms. The SMD for testosterone in OSA versus non-OSA men is approximately -0.76 to -0.97. In practical terms, this is a clinically meaningful suppression — roughly equivalent to the testosterone difference you might expect between a man in his 40s and the same man a decade or more older. And crucially, this effect is independent of both age and BMI, meaning you cannot explain it away by saying these men are older or heavier. The OSA is suppressing testosterone in its own right, over and above whatever contribution age and weight make.
The consequences are exactly what you would expect from low testosterone: persistent fatigue, reduced libido, loss of morning erections, difficulty building or maintaining muscle, increased fat deposition particularly at the abdomen, mood changes including irritability and low mood, and impaired concentration. Many men pursue testosterone replacement therapy before anyone has evaluated their sleep. In some, the OSA is the underlying problem, and the right first intervention is to treat the airway.
Men with OSA have significantly lower testosterone, independent of age and BMI. The suppression is roughly equivalent to what you would expect from ageing an additional decade — driven by what happens in the airway during sleep.
Erectile Dysfunction
The evidence for the link between OSA and erectile dysfunction is clear and consistent. Men with OSA are 82 per cent more likely to have erectile dysfunction — a relative risk of 1.82, meaning almost double the risk. To translate that into real-world numbers: erectile dysfunction of some degree affects roughly 1 in 4 men over 40. With untreated OSA, that moves to closer to 1 in 2. This is not a marginal statistical finding.
The mechanism is multifactorial. Low testosterone reduces libido and contributes to impaired erectile response. Endothelial dysfunction — when OSA impairs the ability of blood vessel walls to relax and dilate — prevents the blood vessel response required for erection. Elevated sympathetic nervous system tone (the body's emergency alarm system, chronically activated by repeated apnoea events) opposes the parasympathetic activation that normal erection requires. All of these mechanisms are present simultaneously in severe OSA.
The treatment signal is one of the cleaner ones in the field. A meta-analysis of 9 studies found that CPAP therapy significantly improves erectile function scores in men with OSA, measured using a standardised questionnaire called the International Index of Erectile Function. The result was statistically robust well beyond what would occur by chance. The effect is greatest in those with pre-existing erectile dysfunction before CPAP was started, and appears to be mediated partly by improved testosterone levels in those whose testosterone recovers with treatment, and partly by improved endothelial function.
Muscle Mass, Strength, and Body Composition
This is the area I think is most underappreciated by men who are otherwise health-conscious and take their training seriously. Obstructive sleep apnoea does not simply make you tired. It creates a hormonal and metabolic environment that actively works against muscle building and maintenance.
A 2024 US population study using data from nearly 3,200 people found that OSA patients have twice the prevalence of sarcopenia (muscle loss) compared with those without OSA — 12 per cent versus 5.5 per cent. Expressed differently, this means that out of every 100 people with OSA, 12 have significant muscle loss, compared with only 5 or 6 out of every 100 people without OSA. In regression analysis — a statistical technique that isolates one factor from others — OSA independently raised the odds of sarcopenia by 50 per cent after adjusting for BMI, age, and other confounders.
The key mechanism here involves a hormone called IGF-1 (insulin-like growth factor 1), which is the downstream signal of growth hormone and the primary driver of muscle protein synthesis and recovery from exercise. A meta-analysis pooling results from 34 separate studies found that OSA patients have significantly lower IGF-1 levels across nearly all subgroups, and the suppression is worse the more severe the OSA. What this means practically: after a training session, the anabolic response — the biological signal that tells your muscles to repair and grow — is blunted in a man with untreated OSA. The recovery signal is suppressed precisely when it should be working hardest.
Add to this the elevated cortisol (the stress hormone, which promotes muscle protein breakdown and fat storage at the abdomen), the low testosterone (which reduces the satellite cell activity required for muscle regeneration), and the insulin resistance (which impairs glucose uptake into muscle cells after exercise), and you have a hormonal environment that is comprehensively opposed to the goals of anyone who trains regularly or wants to maintain their physique into middle age and beyond.
Belly Fat and Adipokine Disruption
The accumulation of visceral abdominal fat in men with OSA is driven by identifiable hormonal mechanisms, not simply by reduced activity or poor diet. I find this important to explain clearly because it has real implications for why standard advice about diet and exercise can feel ineffective for men with undiagnosed sleep apnoea.
OSA suppresses adiponectin — a hormone produced by fat tissue that promotes fat burning, improves insulin sensitivity, and is protective against cardiovascular disease. In men with OSA, adiponectin levels are substantially lower than in men without it. When adiponectin is suppressed, the metabolic environment actively favours fat storage over fat oxidation.
Simultaneously, OSA produces leptin resistance. Leptin is the satiety hormone — it signals to the brain that the body has sufficient energy stores and reduces appetite. In OSA patients, leptin levels in the blood are often elevated (the body is trying harder), but the brain has become resistant to the signal, so hunger remains elevated despite the fat already present. This is analogous to insulin resistance in diabetes: the hormone is there, but the system has stopped listening to it. And elevated cortisol from repeated overnight stress responses promotes specifically visceral (abdominal) fat deposition — the fat around the organs that carries the highest cardiovascular and metabolic risk.
The fat that accumulates immediately around the heart — called epicardial adipose tissue — also increases progressively with OSA severity: mildly in mild OSA, and substantially in severe OSA. This fat is metabolically active, secreting inflammatory signals that contribute to cardiovascular risk independently of its mechanical effects.
Sperm Quality and Male Fertility
The direct evidence specifically on OSA and sperm quality is thinner than for other outcomes, but the mechanistic pathways are well established. Sleep deprivation and disruption raise cortisol (which suppresses the hormonal cascade that drives sperm production), increase testicular oxidative stress, and can disrupt the blood-testis barrier — all of which are known causes of reduced sperm quality, motility, and DNA integrity. A Mendelian randomisation study — the type of analysis using genetic information as a natural experiment to test causation — confirmed that sleep traits causally affect bioavailable testosterone levels, linking sleep biology to male reproductive function at the genetic level. This is an area where the mechanism is coherent and the indirect evidence is strong, even though large OSA-specific sperm studies are not yet available.
What Treatment Does
The treatment picture here is encouraging with appropriate nuance. CPAP clearly and consistently improves erectile function in men with OSA. For testosterone, some studies show recovery of testosterone levels after CPAP, others show no significant change, and the variation is probably explained by whether the baseline testosterone was truly OSA-driven or whether other factors (age, obesity, underlying testicular function) are the dominant determinant.
My clinical approach is to treat the OSA first, allow three to six months of consistent treatment, and then reassess testosterone levels before making any decision about testosterone replacement therapy. Adding TRT before treating OSA misses the root cause, and TRT itself can suppress natural testosterone production and affect haematocrit (the thickness of the blood), and at higher doses can worsen OSA through unclear mechanisms.
For muscle mass and body composition, improving sleep architecture through OSA treatment restores the anabolic hormonal environment over time: growth hormone pulses normalise, IGF-1 begins to recover, and cortisol exposure reduces. This does not happen overnight, but over months of consistent treatment, the hormonal environment becomes progressively less hostile to the goals that most of these patients already have through their training.
References
[1] Wang C et al. Effects of obstructive sleep apnea and its treatment on testosterone levels: a systematic review with meta-analysis. Journal of Endocrinological Investigation. 2022. Meta-analysis; significantly lower testosterone in men with OSA, SMD -0.97, independent of age and BMI.
[2] Su K et al. Association between testosterone and obstructive sleep apnea: a systematic review and meta-analysis. Andrology. 2021. Meta-analysis; SMD -0.76 for testosterone in OSA patients; effect greatest in severe OSA subgroup.
[3] Liu L et al. Association between obstructive sleep apnea and erectile dysfunction: a meta-analysis. ISRN Urology. 2015. Meta-analysis; pooled RR 1.82 for erectile dysfunction in OSA patients (95% CI 1.12-2.97).
[4] Valentina L et al. Obstructive sleep apnea and sexual dysfunction in men: a systematic review and meta-analysis. Journal of Sexual Medicine. 2024. 9 studies; CPAP significantly improved IIEF scores (Z=4.84, statistically robust result).
[5] Tao X et al. Obstructive sleep apnea is associated with increased risk of early-onset sarcopenia and sarcopenic obesity: results from NHANES 2015-2018. International Journal of Obesity. 2024. 3,219 participants; OSA associated with OR 1.5 for sarcopenia and OR 1.8 for sarcopenic obesity; CRP and HOMA-IR as partial mediators.
[6] He J et al. The correlation of serum/plasma IGF-1 concentrations with obstructive sleep apnea hypopnea syndrome: a meta-analysis and meta-regression. Frontiers in Endocrinology. 2022. 34 studies; significantly reduced IGF-1 in OSA patients; negative correlation between IGF-1 and AHI severity.
[7] Najafi AH et al. Evaluation of plasma/serum adiponectin levels in adult patients with obstructive sleep apnea syndrome: a systematic review and meta-analysis. Life. 2022. 28 articles, 36 studies; pooled SMD -0.71 for adiponectin in OSA patients versus controls.
[8] Song G et al. Association of epicardial adipose tissues with obstructive sleep apnea and its severity: a meta-analysis study. Nutrition, Metabolism and Cardiovascular Diseases. 2020. 9 studies, 1,178 participants; progressive increase in cardiac fat by OSA severity (mild +0.62mm, moderate +0.83mm, severe +1.06mm).
Contact Professor Vik Veer
If you would like to discuss a sleep assessment or arrange a consultation, please use the details below.
Private secretary: 0207 458 4584