Natural testosterone optimisation: what actually moves the needle

Most of what genuinely moves testosterone in men is unglamorous and free: enough sleep, a lean body, hard resistance training as part of an active life, and eating enough food and fat. Correcting a real zinc or vitamin D deficiency helps; topping up when you are already replete does not, and almost every product sold as a “test booster” does nothing measurable. This guide separates the real levers from the marketing, sets out the symptoms that should prompt a test and how to read the results in a UK setting, and gives a frank account of testosterone replacement therapy and its tradeoffs.

What testosterone is, and what normal looks like

Testosterone is the main male androgen, made mostly in the testes under instruction from the brain: the pituitary releases luteinising hormone (LH) and follicle-stimulating hormone (FSH), and LH tells the testes to produce testosterone. It drives libido, erections, muscle and bone maintenance, red blood cell production and a share of energy and mood. Levels peak in early adulthood and drift down slowly with age, by very roughly 1% to 2% a year from the late thirties, though this is steepened far more by ill health and weight gain than by age alone.

Most circulating testosterone is not freely available. Roughly half is bound tightly to sex hormone-binding globulin (SHBG), most of the rest is loosely bound to albumin, and only around 1% to 2% floats free. This matters for interpreting a blood test, because anything that shifts SHBG, including age, obesity, thyroid disease, liver disease and some medicines, changes the total number without necessarily changing what your tissues actually experience.

The real levers that move testosterone

The honest hierarchy is short, and notably none of it is a pill you buy from a sports nutrition shop.

Lose excess body fat

This is the most powerful lever for the men most likely to be reading this. Fat tissue contains the enzyme aromatase, which converts testosterone into oestrogen, and obesity drives the insulin resistance and inflammation that suppress the brain signals to the testes. The result is a common, often reversible state called obesity-associated hypogonadotropic hypogonadism. A systematic review and meta-analysis by Corona and colleagues, pooling 44 studies in 1,774 men, found that weight loss reliably reverses it: total testosterone rose by an average of 4.8 nmol/L, more with greater weight loss.² For many men carrying significant excess weight, fat loss alone moves them from the low range back into normal.

Protect your sleep

Testosterone is produced in a daily rhythm tied to sleep, peaking in the early morning. In a tightly controlled study by Leproult and Van Cauter, ten healthy young men who slept under five hours a night for one week saw daytime testosterone fall by 10% to 15%, an effect equivalent to ageing 10 to 15 years.³ Obstructive sleep apnoea, common in overweight men, independently suppresses testosterone too, so if you snore heavily or wake unrefreshed, that is worth investigating before you blame your hormones.

Train, and stay generally active

Resistance training is non-negotiable for the things people actually want from testosterone, namely muscle, strength and body composition, but the evidence that it durably raises your resting testosterone is weak. A 2022 systematic review and meta-analysis in insufficiently active men found that exercise training had a negligible effect on resting total or free testosterone, with the modest signal coming more from aerobic and interval work than from lifting.⁶ The brief post-workout spike does not predict muscle gain either. Train hard because it builds the physique and metabolic health that matter and helps keep you lean, not because it reliably raises a blood number. We cover the wider hormone-and-muscle story in our piece on growth hormone and IGF-1.

Eat enough food, and enough fat

Testosterone production is sensitive to energy availability: sustained heavy calorie restriction, very low body fat and overtraining can all suppress it, a pattern seen in endurance athletes and men crash-dieting. Dietary fat matters too. A meta-analysis by Whittaker and Wu of six controlled studies found that low-fat diets reduced total testosterone compared with higher-fat diets, with a standardised mean difference of about -0.38.⁴ The sample was small, so do not over-read it, but the practical message is sound: extreme low-fat eating is not a friend of testosterone, and a balanced diet with adequate calories and a normal proportion of fat is the supportive baseline.

Correct a deficiency, but only a real one

Two micronutrients have a genuine, mechanistic link to testosterone: zinc and vitamin D. The crucial word is deficiency. A systematic review of zinc found that the effect of supplementation depends on where you start: correcting a deficiency can raise testosterone, but adding zinc on top of adequate levels does little.⁷ Vitamin D is murkier: some meta-analyses of randomised trials report a small rise in total testosterone, others find no significant effect, and the picture is genuinely conflicting.⁸ The reasonable position: if you are deficient, fixing it is worthwhile and may nudge testosterone; if your levels are already fine, neither is a booster. UK adults are advised to consider a vitamin D supplement in the darker months regardless, which we cover in our vitamin D guide.

What does not work: the booster industry

Any supplement shop carries shelves of “test boosters” built on tribulus, fenugreek, D-aspartic acid, ashwagandha, maca, boron and proprietary blends, and the evidence that any of them meaningfully raises testosterone in men who are not deficient is weak to non-existent. A 2023 systematic review by Aguilar-Morgado, Morgentaler and colleagues examined 52 studies covering 27 proposed ingredients across athletes, infertile men, men with late-onset hypogonadism and healthy men, and found that most showed no consistent benefit on serum total testosterone versus placebo.⁹ A separate analysis by Balasubramanian and colleagues of 50 best-selling products found that only about 24.8% contained any component with published evidence of raising testosterone, around 10% contained an ingredient shown to lower it, and most used ingredients never studied for the purpose.⁵ Where a small signal exists, for instance tribulus or D-aspartic acid, the better-designed trials tend to find no durable effect in healthy men.

Symptoms of genuinely low testosterone

The symptoms men worry about, tiredness, low mood and poor concentration, are real but notoriously non-specific: they overlap with poor sleep, stress, depression, thyroid problems and simply being unfit. The symptoms that point most specifically to low testosterone are sexual. The large European Male Ageing Study by Wu and colleagues, surveying 3,369 men aged 40 to 79, found that the combination of three sexual symptoms, reduced libido, fewer morning erections and erectile dysfunction, was the strongest clinical predictor of genuinely low testosterone.¹⁰ Other recognised features include loss of muscle and strength, increased central body fat, reduced body hair, hot flushes and low bone density over time.

The key clinical point, and the one most often missed, is that low testosterone should be diagnosed from symptoms plus a confirmed low blood level together, never from a number alone or symptoms alone. A man with a borderline reading and no sexual symptoms is very unlikely to benefit from treatment.

When to get tested in the UK, and how to read it

If you have the suggestive symptoms above, particularly the sexual cluster, it is reasonable to ask your GP for a test. The NHS recognises this picture, sometimes loosely called the “male menopause,” and will investigate when symptoms warrant it.¹¹ The testing rules are specific and worth knowing, because doing it wrong produces misleading numbers.

• Time it correctly. Testosterone peaks in the morning, so the sample should be taken between roughly 7am and 11am, ideally fasted.
• Confirm it. A single low result is not enough. UK guidance requires two separate morning samples showing a low total testosterone before a diagnosis is made.¹
• Do not test when acutely unwell. Acute illness, recent surgery and short-term stress all transiently lower testosterone and can produce a false low.

The 2023 joint position statement from the Society for Endocrinology and the Association for Clinical Biochemistry and Laboratory Medicine sets out how to interpret the results.¹ A total testosterone consistently above 12 nmol/L makes deficiency unlikely; consistently below 8 nmol/L, with symptoms, supports it; the zone in between is where SHBG and free testosterone earn their place. Crucially, when SHBG is normal a calculated free testosterone adds nothing beyond the total. It becomes useful only when SHBG is abnormal: a high SHBG (common with age, thyroid overactivity or liver disease) can drag the total down while the free level is adequate, and a low SHBG (common with obesity and insulin resistance) can mask a genuinely low free level. Note too that most UK free values are calculated from total testosterone, SHBG and albumin, as the gold-standard direct measurement is not routinely available.

If two morning samples confirm a low level, the next step is to find out why. Measuring LH and FSH separates a testicular problem (high LH and FSH) from one in the brain’s signalling (low or inappropriately normal LH and FSH), and prolactin and iron studies rule out treatable causes. It is the same logic-first approach we apply across our insights: confirm the abnormality, then chase the cause, before reaching for treatment.

TRT: what it does and what it costs you

Testosterone replacement therapy, given as a gel or injection, genuinely helps men with confirmed hypogonadism: it reliably improves libido and sexual function, modestly increases muscle mass and bone density, and can lift mood and energy in those who are truly deficient. For a man with two morning readings under 8 nmol/L and clear symptoms, it is an evidence-based treatment, not a vanity intervention. The tradeoffs are real, though, and matter more because TRT is increasingly sold privately to men whose levels are not actually low.

• Fertility. This is the big one. External testosterone suppresses the brain signals that drive the testes, switching off the body’s own production and sperm formation, and azoospermia (no sperm) develops in a large majority of men within a few months of starting.¹² It is usually reversible after stopping, over several months to a couple of years, but any man who may want children should not start TRT without discussing fertility-sparing options such as hCG first.
• It is usually for life. Because TRT suppresses natural production, stopping often leaves you worse than baseline for a while. It is a long-term commitment requiring ongoing monitoring.
• Blood thickening and other effects. Testosterone raises red blood cell count (haematocrit), which must be monitored to avoid an excessively thick blood and clot risk. It can also worsen sleep apnoea and cause acne and breast tenderness.
• Cardiovascular and prostate questions. The large TRAVERSE randomised trial in 5,204 men with low testosterone and high cardiovascular risk found TRT was not inferior to placebo for major cardiac events over about two years, which was reassuring, but it did record more cases of atrial fibrillation and other arrhythmias.¹³ TRT does not appear to cause prostate cancer but requires prostate monitoring.

This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.