Testosterone has become a favourite topic online, and a sales pitch along with it. The observation underneath it is real: young men measure lower than earlier generations did at the same age. That does not mean your levels are low, and it is not a reason to order a tub of anything. It is a reason to look at three things you actually control.
What the measurements show
The US national health survey (NHANES) went through blood values from 4,045 young men across 1999-2016. Mean total testosterone fell from 605 ng/dl to 451 ng/dl. The difference held after age, body mass index, illness, alcohol, smoking and physical activity were accounted for.
A wider review points the same way. A 2025 systematic review covered 1,256 studies and more than a million men from 1970-2024. The later the measurement, the lower the testosterone, and the decline showed up in every age group even after adjusting for age and body mass index. Luteinising hormone, the pituitary’s signal to the testes, fell at the same time. The authors read that as the regulation having shifted rather than the testes being broken.
Two honest caveats. Assays and study samples vary across decades, so part of the gap may be measurement rather than men. And a population average says nothing about your own value: the spread between individuals is enormous.
Why this is not just a hormone number
Testosterone is not a masculinity gauge. It is one regulated part of metabolism, and it responds to the same things that decide the rest of your health: how much fat you carry, how much you move, how much you eat and how much you sleep. That is why the top of the list is not a supplement but a boring trio.
1. Hard training
Low testosterone tied to excess weight is the best studied and most reversible part of this equation. A meta-analysis pooling 24 trials found that losing weight raised total testosterone: by an average of 2.9 nmol/l on a low-calorie diet and by 8.7 nmol/l after bariatric surgery. The bigger the weight loss, the bigger the rise.
Strength training does the same job more slowly and more durably. It builds muscle, improves insulin sensitivity and keeps weight loss from eating your muscle. The hormone spike right after a single session, on the other hand, is not worth chasing: it passes quickly and predicts very little.
In practice: 3-4 strength sessions a week, big compound lifts, progression written down, and daily movement on top. Hard training also means leaving room for recovery around it.
2. Eating enough, not just eating less
Undereating lowers testosterone just as reliably as excess weight does. When energy intake stays too low relative to training, the body turns the reproductive axis down and both luteinising hormone and testosterone fall. In athletes this is known as relative energy deficiency (RED-S), and it happens to men too. The good news is that it is fixed by eating and resting.
The amount of fat matters as well. In a meta-analysis of six controlled studies (206 men), moving from roughly 40 percent of energy from fat to roughly 20 percent lowered total testosterone by 10-15 percent on average. The studies were small and short, so this is no reason for dogma, but cutting fat to the floor is not hormonally free.
In practice: eat enough to train, about 1.6-2.2 grams of protein per kilo of body weight, roughly a quarter of your energy from fat, and lose weight at a sane pace instead of in crash diets.
3. Sleeping enough
Ten healthy young men (average age 24) slept under five hours a night for eight nights in a lab. Their daytime testosterone dropped by 10-15 percent, which the researchers compared to 10-15 years of ageing. The sample was small and the window short, so one study settles nothing. The direction is still logical, because most of the day’s testosterone production happens while you sleep.
In practice: 7-9 hours, the same wake-up time on weekends, and the last hours of the evening without alcohol and bright light.
What not to do
Do not buy a booster. Zinc and vitamin D fix a deficiency if you have one, but they do not raise levels that are already fine.
Do not diagnose yourself from a mood or an online quiz. If you have symptoms such as constant fatigue, lower libido, low mood or vanishing strength, the sample is taken in the morning, repeated, and read by a doctor.
Do not start testosterone replacement in place of fixing your habits. It is a treatment for diagnosed deficiency. Exogenous testosterone shuts down your own production and impairs sperm production, and starting it is a decision to make with a doctor.
The week that does most of the work
- 3-4 strength sessions, big lifts, progression logged
- 8,000-10,000 steps a day and a couple of easier cardio sessions
- protein at every meal and enough energy for the training you do
- 7-9 hours of sleep on a steady rhythm
- alcohol kept moderate
- waist circumference in a sensible range
The list is boring, and that is the point. The factors that surface in the population studies are the ones you can act on today. They also compound: log your training, your food and your sleep, and in three months you can see what actually changed.
Sources
- Lokeshwar et al. (2021): Decline in Serum Testosterone Levels Among Adolescent and Young Adult Men in the USA, European Urology Focus.
- Santi et al. (2025): Temporal trends in serum testosterone and luteinizing hormone levels, Journal of Endocrinological Investigation 48(11).
- Corona et al. (2013): Body weight loss reverts obesity-associated hypogonadotropic hypogonadism, European Journal of Endocrinology 168(6).
- Whittaker & Wu (2021): Low-fat diets and testosterone in men, Journal of Steroid Biochemistry and Molecular Biology.
- Leproult & Van Cauter (2011), JAMA: Effect of 1 week of sleep restriction on testosterone levels in young healthy men.
- Review (2020): Hypogonadism in Exercising Males: Dysfunction or Adaptive-Regulatory Adjustment?, Frontiers in Endocrinology.