What really affects your testosterone?
We analysed nearly 10,000 men to find out
Feeling less energetic than you used to? You might assume it’s just age catching up with you, but sometimes, it’s down to testosterone. And while it’s natural for testosterone levels to decline over the years, we found something surprising: age isn’t the main driver. Your waistline is.
We looked at the test results from nearly 10,000 UK men*, including their testosterone levels, weight, blood sugar, age, sleep quality, exercise habits, and even the time of day they took their test. Then we compared our findings with what decades of research actually shows.
So, here’s what moves the needle, and what doesn’t.
In this article, we cover:
1. Weight: the dominant factor
Weight is the single most powerful modifiable factor for testosterone. A 2023 meta-analysis of 44 studies found men who lost significant weight gained 2.5–7.2 nmol/L of testosterone [1]. The European Male Aging Study found obese men face an 8.7-fold increased risk of low testosterone compared to normal-weight men [2].
But what’s weight got to do with it? Well, excess fat tissue converts testosterone to oestrogen, and inflammation and insulin resistance further suppress production. It creates a vicious cycle where low testosterone makes it harder to lose weight, and excess weight lowers testosterone further.
What we found
Among nearly 10,000 men, we found a similar pattern. For every 10-point increase in BMI (for example, 25 to 35), testosterone dropped 4.2 nmol/L, even when accounting for age. Obese men had a significantly lower testosterone level compared to all other BMI groups.
The takeaway: Maintaining a normal BMI can significantly impact your T levels.
2. Blood sugar: effects beyond weight
Research shows that raised blood sugar and diabetes affect testosterone levels independently of weight [3]. But having diabetes and obesity is a double hit: about half of these men have low testosterone [4].
What we found
Men with higher blood sugar levels tended to have a higher BMI. But even when taking weight out of the picture, having higher blood sugar levels was still linked with lower testosterone levels.
Combining being overweight and raised blood sugar is even worse (see heatmap below). Men with the highest BMI and blood sugar had an average testosterone level of 13.9 nmol/L, a whole 35% lower compared with men in the lowest categories.
The takeaway: Pre-diabetes and diabetes can directly impact your testosterone levels, even if you’re not obese. Try to keep your blood sugar levels in check.
3. Age: it matters, but less than you think
The NHS suggests that testosterone declines around 1% every year from around the age of 30 to 40 [5]. That works out to be around 1 nmol/L per decade, with a steeper drop from age 80 onwards [6].
What we found
Our data showed a modest decline. Men in their 20s averaged 18.5 nmol/L, dropping to 17.3 nmol/L by their 50s. This is somewhat lower than some research suggests, possibly because our dataset includes health-conscious men who’ve taken proactive steps to get tested.
But here’s what matters most: variation between men at the same age far outweighs the average decline. In other words, within any age group, there is a huge variation between the highest and lowest result. A 45-year-old could easily have double the testosterone of a 25-year-old. It comes down to a number of factors, including genetics , weight, and more.
The takeaway: If your testosterone is low at 50, don’t just assume it’s age. Age contributes to maybe a 1-2 nmol/L decline, but other factors – especially weight – are likely to have a bigger impact.
4. Test timing: morning is critical
Testosterone peaks in early morning and declines throughout the day. Young men experience drops of up to 25% from morning to afternoon, while men in their 70s are more likely to show a 10% daily variation [7].
What we found
As expected, average testosterone levels were highest in the early morning, and took a fairly sharp decline from late morning onwards. Samples taken later in the day were, on average, as much as 20% lower than samples taken at 6am.
The takeaway: Always test before 11am where possible. An afternoon test could show borderline low when you're actually normal. This matters most if you're younger, when daily variation is strongest.
5. Exercise: the uncomfortable truth
Let’s start with men who have normal testosterone levels to begin with. Multiple studies have found exercise training has very little, if any, long-term effect on testosterone. One 2021 analysis of 11 studies with 421 men found no benefit from resistance training, aerobic exercise, or combined programmes [8]. Another systematic review on older men found that resistance training had no effect, but aerobic and interval training had a very small effect on testosterone [9].
What about if you’re overweight or obese?
This is where exercise is likely to show the biggest benefit. Apart from its positive effects on overall health and mood, exercise is shown to increase testosterone in obese men [10]. However, the benefit comes primarily from losing body fat.
What we found
When separating men by weight category, a clear pattern emerged. Among normal-weight men, strength training showed no correlation with testosterone (r = -0.014, not significant). Among obese men, however, the correlation was positive (r = 0.158, p = 0.012). This means that obese men who reported higher levels of exercise tended to have slightly higher testosterone levels.
The takeaway: Exercise for your heart, muscles, mood, weight and overall health. If you're carrying extra weight, it might help your testosterone levels too. However, if you already have a normal BMI, don't expect exercise alone to boost your testosterone.
6. Sleep: why catching Zs is important for T
Solid research on sleep and testosterone is surprisingly limited, but a 2021 meta-analysis looking at 18 studies, attempted to settle the debate [11]. Their conclusion was that short-term partial sleep deprivation has no significant effect on testosterone levels. However, total sleep deprivation did have a considerable impact. Basically, don’t pull an all-nighter – it’s not going to do your hormones any favours.
What we found
Since our customer data is self-reported, we should take any conclusions with a pinch of salt. Sleep quantity (r= 0.064) had a slightly bigger impact on testosterone than sleep quality (r= 0.044), but both showed a pretty weak correlation.
The takeaway: Don't dismiss sleep based on our data. If you're consistently getting under 6 hours or have symptoms of sleep apnoea (loud snoring, daytime fatigue, observed breathing pauses), addressing this could meaningfully affect testosterone. In particular, sleep apnoea deserves medical attention. It's both treatable and significantly impacts hormone health.
The bottom line
If there’s one clear message from both our data and decades of research, it’s this: testosterone is far more influenced by metabolic health than by age alone.
For most men, excess weight is the biggest modifiable factor. Losing body fat can lead to meaningful increases in testosterone, often far greater than the slow, age-related decline most people worry about. Blood sugar control matters too, even independently of weight, and poor sleep or mistimed testing can muddy the picture further.
Age still plays a role, but it’s a smaller one than commonly assumed. Two men of the same age can have wildly different testosterone levels, depending on factors like weight, insulin resistance, sleep, and overall health.
In short, low testosterone isn’t just something that just happens with age. In many cases, it reflects underlying, and often addressable, health factors. Understanding which ones apply to you is the first step toward doing something about it.
*A note on our analysis
This article combines findings from our analysis of nearly 10,000 Medichecks customers with established research from systematic reviews and clinical trials. Our data provides a real-world snapshot of UK men, but it has limitations: it's observational (not experimental), relies on self-reported lifestyle data, and represents a single point in time rather than tracking changes over months or years. Where our findings differ from controlled studies, we've noted why and deferred to the stronger evidence. Think of our data as confirming what research already shows, not as the primary proof.
Based on 9,547 Medichecks male customers (Dec 2024-Nov 2025) who had taken a test containing total testosterone, free testosterone, and HbA1c. BMI was only included in the analysis if it was recorded within one year of their test results. For lifestyle analysis, men were only included if they’d completed this information. For men with multiple results over this period, one result was taken at random. Averages are given as medians.
References
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- Tajar A, Forti G, O’Neill TW, Lee DM, Silman AJ, Finn JD, et al. Characteristics of Secondary, Primary, and Compensated Hypogonadism in Aging Men: Evidence from the European Male Ageing Study. J Clin Endocrinol Metab. 2010;95: 1810–1818. doi:10.1210/jc.2009-1796
- Watts M. A number of the symptoms of low testosterone are similar to some of the symptoms of type 2 diabetes and health statistics indicate that the two conditions may be associated with eachother. In: Diabetes [Internet]. 15 Jan 2019 [cited 15 Dec 2025]. Available: https://www.diabetes.co.uk/low-testosterone-and-diabetes.html
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- The “male menopause.” In: nhs.uk [Internet]. 3 Oct 2018 [cited 16 Dec 2025]. Available: https://www.nhs.uk/conditions/male-menopause/
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- Potter NJ, Tomkinson GR, Dufner TJ, Walch TJ, Roemmich JN, Wilson PB, et al. Effects of Exercise Training on Resting Testosterone Concentrations in Insufficiently Active Men: A Systematic Review and Meta-Analysis. J Strength Cond Res. 2021;35: 3521–3528. doi:10.1519/JSC.0000000000004146
- Hayes LD, Elliott BT. Short-Term Exercise Training Inconsistently Influences Basal Testosterone in Older Men: A Systematic Review and Meta-Analysis. Front Physiol. 2019;9: 1878. doi:10.3389/fphys.2018.01878
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