5 Warning Signs of Low Testosterone Every Man Should Know

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Written by Dr Imran Haq, GP (MRCGP) UK-based General Practitioner with interests in Men’s Health and Endocrinology. Educational article | Updated January, 2025

Testosterone is a vital male hormone responsible for more than just sex drive and muscle mass. It plays a key role in energy levels, mood, cognitive function, bone health, and has recognised associations with cardiovascular health. Yet, testosterone deficiency often goes undiagnosed, partly due to stigma, and partly because the symptoms can be subtle or mistaken for normal ageing.

According to the European Male Ageing Study (EMAS), testosterone deficiency (TD) affects around 2.1% of men aged 40–79, with rates increasing as men get older. And yet, awareness remains low. In fact, a 2012 survey of GPs in South Staffordshire CCG found that while 68% of female GPs listed women’s health as a clinical interest, only 1% of male GPs listed men’s health.

As a GP with a special interest in men’s health, here are five key signs of low testosterone that every man should know and what to do about them.

1. Low Libido and Erectile Dysfunction

One of the earliest and most common symptoms of testosterone deficiency is a reduced sex drive. Men may also experience erectile dysfunction or difficulty maintaining an erection. While these issues can stem from various causes, testosterone deficiency should always be considered, especially if other symptoms are present.

2. Fatigue and Lack of Energy

Persistent tiredness, even after adequate sleep, can be a hallmark of low testosterone. Many men report that they feel they’ve lost their “get up and go”, both physically and mentally. This can interfere with daily life, productivity, and exercise motivation.

3. Low Mood, Irritability, or Brain Fog

Testosterone has a known influence on mood and cognitive function. Deficiency can contribute to low mood, increased irritability, or even symptoms resembling depression. Some men also report difficulty with concentration or memory, often described as “brain fog.”

4. Loss of Muscle Mass and Increased Body Fat

If you’re losing strength despite regular workouts or noticing more belly fat, low testosterone may be playing a role. The hormone is essential for maintaining lean muscle mass and regulating fat distribution.

5. Reduced Physical Performance and Recovery

Struggling with stamina or noticing slower recovery from exercise or injury? Testosterone supports physical endurance and recovery. Low levels can make it harder to bounce back and may lead to decreased athletic performance or joint discomfort.

Long-Term Health Risks of Testosterone Deficiency

If left untreated, testosterone deficiency can contribute to more serious health issues over time, including:

  • Increased body fat and reduced stamina
  • Anaemia
  • Loss of body hair and muscle bulk
  • Metabolic syndrome (a combination of high blood pressure, high blood sugar, abnormal cholesterol, and central obesity)
  • Type 2 diabetes and cardiovascular disease
  • Osteoporosis (bone thinning)
  • Depression and decreased quality of life

What Causes Low Testosterone?

Testosterone deficiency can be due to a range of factors:

  • Ageing (natural decline from mid-30s onward)
  • Certain medications, especially long-term opioids
  • Testicular injury or cancer
  • Past infections like mumps
  • Chronic illnesses (e.g., type 2 diabetes, kidney or liver disease, HIV/AIDS)
  • Genetic conditions (e.g., Klinefelter syndrome, haemochromatosis)
  • Pituitary gland issues (e.g., tumours affecting hormone production)

How Is Testosterone Measured?

If your GP thinks it’s appropriate, testosterone can be measured via a blood test, ideally:

  • In the morning (between 07:00–11:00), when levels are naturally highest
  • In a fasting state, for the most accurate reading
  • When you’re well, as illness (like a cold or viral infection) can affect results

Additional tests may include PSA (prostate-specific antigen) and a full blood count to screen for anaemia.

A comprehensive history is also essential, as testosterone deficiency can present with both sexual and general health symptoms. The diagnosis and management of testosterone deficiency should always follow current UK established clinical guidelines from the British Society for Sexual Medicine (BSSM) and other expert consensus statements and involve careful assessment of symptoms, biochemical confirmation with repeat testing, and consideration of contraindications. Testosterone replacement therapy is not appropriate for all men and requires ongoing monitoring for efficacy and safety.

Lifestyle Changes That May Support Healthy Testosterone

While medical evaluation is essential, evidence suggests the following lifestyle strategies may support natural testosterone levels:

  • Healthy Fats: Testosterone is synthesised from cholesterol. Include healthy fats from olive oil, avocado, nuts, eggs, and oily fish. Limit saturated fats, and focus on monounsaturated and omega-3 fats. [1,2]
  • Vitamin D3 & Omega-3: Some observational and interventional studies suggest that vitamin D and omega-3 status may be associated with testosterone levels; however, evidence remains mixed, and supplementation should be considered adjunctive rather than therapeutic. [3]
  • Sleep: Testosterone is mostly produced during deep sleep. Less than 5 hours of sleep per night may reduce levels by up to 15%. [4]
  • High-Intensity Exercise: Regular resistance training or HIIT can temporarily boost testosterone.
  • Manage Stress: Chronic stress elevates cortisol, a hormone that suppresses testosterone.

Common Myths About Low Testosterone

  • Myth: Only older men are affected.
    • Fact: While levels decline with age, younger men can also experience testosterone deficiency.
  • Myth: It’s rare.
    • Fact: NHS Diabetes data reports that 16% of men with type 2 diabetes have below-normal testosterone levels.
  • Myth: Only sexual symptoms matter.
    • Fact: Fatigue, mood changes, and physical decline may all be early signs.

When to See Your GP

If you’re experiencing any of the symptoms described above, especially if they’re affecting your quality of life, speak to your GP. A simple blood test and history could help uncover the cause. Your GP can advise on next steps — whether it’s lifestyle change, further investigation, or referral.

Conclusion

Low testosterone is more than just a sexual health issue, it can al affect your energy, your body, and your long-term health. The good news is that awareness is growing, and many cases can be improved with the right support.

Taking care of your hormone health is an important part of ageing well. If you found this blog useful, share it with someone who might benefit.

Stay Connected

Connect with Dr Imran on LinkedIn for more evidence-based men’s health content.

This article is intended for educational purposes and reflects current primary care perspectives on testosterone deficiency.

References

  1. Volek JS et al. Dietary fat and testosterone in resistance-trained men. J Appl Physiol. 1997.
  2. Smith GI et al. Fish oil–derived n-3 PUFA intake increases muscle mass and function in healthy older adults. Am J Clin Nutr. 2015.
  3. Pilz S et al. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res. 2011.
  4. British Society for Sexual Medicine (BSSM). Guidelines on Adult Testosterone Deficiency and Testosterone Replacement Therapy in Men. BSSM, UK. https://bssm.org.uk/wp-content/uploads/2023/02/BSSM-Practical-Guide-High-Res-single-pp-view-final.pdf Latest Update.
  5. Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011.
  6. British Society for Sexual Medicine (BSSM). Educational Module on Adult Testosterone Deficiency. In collaboration with PCTAG. bssm.org.uk (Accessed July 2025)