Testosterone Replacement Therapy and Cardiovascular Health: Part 1: Optimised, Not Maximised
Why Testosterone Matters for the Heart, Metabolism and Body Composition
Testosterone replacement therapy (TRT) is one of the most discussed topics in men's health at the moment, and one of the most misunderstood.
To some, it's a controversial "anti-ageing" fad. To others, it's an under-used treatment for men who are genuinely deficient. At Orion Medica, we sit closer to the truth: TRT can make a real difference when it's used appropriately, but it isn't about chasing youth, performance or aesthetics; it's about restoring what's missing.
One question that gets asked is whether TRT can improve heart health. The honest answer is yes, it can help, but only in the right scenario.
In men with confirmed testosterone deficiency, restoring testosterone to a normal, healthy range can improve several cardiovascular risk markers — including visceral fat, insulin resistance, anaemia, exercise capacity and body composition. Now, TRT is not a first-line heart treatment, and the goal should never be to push levels above what's normal for a healthy man.
The key word is optimised, not maximised.
Testosterone and the Cardiovascular System
We tend to think of testosterone as the hormone behind libido, muscle and masculinity. In reality, testosterone receptors are found throughout the body — in skeletal muscle, fat tissue, bone marrow, blood vessels and the heart itself.
That means testosterone can influence a surprising number of systems relevant to heart health, including:
body-fat distribution
muscle mass
insulin sensitivity
red blood cell production
inflammation
blood-vessel function
exercise capacity
mood
motivation
physical activity
Low testosterone often shows up alongside obesity, insulin resistance, type 2 diabetes, metabolic syndrome and cardiovascular disease. But the relationship runs both ways → low testosterone can contribute to poor metabolic health, and poor metabolic health can, in turn, suppress testosterone.
This is exactly why proper assessment matters so much to us.
A man with true hypogonadism is in a very different position to a man whose testosterone is temporarily dipped because of poor sleep, excess body fat, alcohol, stress, under-eating, overtraining or illness. Getting this distinction right is the first and most important step.
Diagnoses involves assessing self-reported symptoms of deficiency and low testosterone confirmed through accurate, repeated morning blood tests.
What Does "Optimised" Testosterone Actually Mean?
You'll often hear TRT described as "restoring testosterone to back when you were in your 20s." It's a nice soundbite, but it needs some unpacking.
In clinical practice, the aim isn't to push every man to the very top of a young man's range, and it's certainly not to create the supraphysiological levels seen with anabolic steroid misuse.
A better way to put it is this → restore testosterone to a healthy physiological range, while closely monitoring symptoms, blood markers and side effects.
The American Urological Association recommends aiming for the "middle tertile" of the normal reference range — roughly 450–600 ng/dL, or around 15.6–20.8 nmol/L, depending on the lab and units used.
The UK Society for Endocrinology takes a similar view, recommending that modern testosterone preparations aim for the mid-reference range, while keeping a close eye on haemoglobin and haematocrit.
This balance matters. Being genuinely deficient can cause harm but so can pushing levels too high. Good care sits in the middle.
Why Low Testosterone Can Work Against Your Metabolism
Low testosterone is commonly linked with more visceral fat, less lean mass, lower energy, reduced activity levels, insulin resistance and poorer blood sugar control.
Visceral fat deserves a special mention here. This is the fat stored around your organs rather than under your skin, and it's far more metabolically active. Higher visceral fat is strongly linked to insulin resistance, fatty liver disease, high blood pressure, inflammation and cardiovascular risk.
Testosterone plays into this in a few ways. Low levels make it harder to maintain muscle, and less muscle means less capacity to store and use glucose, since skeletal muscle is one of the body's biggest glucose "sinks." Low testosterone can also sap motivation and training capacity, which can spiral: less movement leads to more fat gain, worse insulin resistance, and further hormonal suppression.
For men who are genuinely deficient, restoring testosterone can help break that cycle. In 2024, a meta-analysis on testosterone therapy and metabolic syndrome found meaningful reductions in waist circumference and triglycerides, along with improvements across several components of metabolic syndrome.
To clarify, this doesn't mean TRT replaces nutrition and exercise. But what it can do, in testosterone-deficient men, is make those lifestyle changes easier to sustain by improving the underlying physiology.
Body Composition: Less Fat, More Lean Mass
One of the most consistent benefits we see with TRT in hypogonadal men is improved body composition.
Testosterone supports muscle protein synthesis and helps preserve lean mass, while also influencing where fat is stored. This matters for heart health because muscle isn't just about how you look. It's a genuinely metabolic organ: it improves glucose handling, supports insulin sensitivity, raises resting energy expenditure, and gives you a functional reserve as you get older.
In a randomised trial of obese men on a weight-loss programme, adding testosterone treatment led to a significant reduction in visceral fat, over and above what weight loss alone achieved.
This is likely where TRT's cardiovascular benefit really comes from. It doesn't "clean the arteries" in some simple mechanical way. Instead, it may improve the upstream drivers of cardiovascular disease → obesity, poor glucose control, low activity, low muscle mass and inflammation.
One important caveat: TRT shouldn't be thought of as a weight-loss drug. Some men gain lean mass while losing fat, so the number on the scales may barely move. Instead, measurements such as waist circumference, body composition, strength, energy, training performance, blood pressure, blood sugar and lipids tell a much more useful story.
Insulin Resistance and Type 2 Diabetes Risk
The link between testosterone and insulin resistance is one of the strongest in this whole picture.
Men with obesity, metabolic syndrome and type 2 diabetes often have lower testosterone — and in some cases, losing weight and improving metabolic health can raise testosterone naturally. The Society for Endocrinology notes that in older men whose low testosterone is linked to obesity or illness, lifestyle changes should usually come first, unless there's a compelling reason for treatment such as osteoporosis, anaemia, small testes or sexual dysfunction that hasn't responded to other approaches.
That said, in men with confirmed deficiency, TRT may help improve insulin sensitivity and reduce diabetes risk in selected cases.
The T4DM trial, published in The Lancet Diabetes & Endocrinology, looked at testosterone treatment alongside a lifestyle programme in men at high risk of type 2 diabetes. Over two years, testosterone treatment reduced the proportion of men who went on to develop diabetes, beyond what lifestyle changes achieved alone.
It's a genuinely encouraging finding, but one to interpret with care. TRT isn't a first-line diabetes-prevention therapy → nutrition, resistance training, weight management, sleep and activity remain the foundation. But for men who are truly deficient, optimising testosterone may improve how well the body responds to those efforts.
Anaemia, Oxygen Delivery and Exercise Capacity
Testosterone stimulates red blood cell production, which can be genuinely helpful for men with testosterone-related anaemia. Treating this anaemia can lift energy, improve oxygen delivery and boost exercise tolerance. Since cardiovascular fitness is one of the strongest predictors of long-term health, anything that improves it is worth taking seriously.
Trials have shown testosterone therapy can significantly raised haemoglobin in older men with low testosterone and unexplained anaemia. By 12 months, haemoglobin had risen by at least 1.0 g/dL in 54% of men receiving testosterone, compared with just 15% on placebo.
But the same mechanism that helps here can also become a risk. If red blood cell production rises too far, haematocrit can climb excessively causing thicker blood, which raises the risk of clotting.
This is exactly why we monitor TRT closely rather than treating it as "set and forget." As a key safety priority, haematocrit levels are checked both before and during treatment.
The Takeaway
Low testosterone isn't just a libido issue. In men who are genuinely deficient, it can contribute to poorer body composition, higher visceral fat, lower lean mass, reduced exercise capacity, insulin resistance and anaemia → all of which feed into cardiovascular risk.
Restoring testosterone to a healthy physiological range can help improve some of these upstream drivers. But it's not a heart drug, a fat-loss drug, or an anti-ageing shortcut.
The real benefit comes from correcting genuine deficiency, improving the underlying physiology, and making it easier to engage with the fundamentals: training, nutrition, sleep, weight management and metabolic health.
In Part 2, we'll look at the cardiovascular safety evidence, the risks of poorly monitored TRT, who's likely to benefit most, and why the goal should always be optimising testosterone never maximising it.
