The Science of Testosterone: What It Does and What Affects It

Understanding Testosterone

Testosterone is a naturally occurring hormone that plays an important role in human health. Although often associated with men, testosterone is present in both men and women. In males, it is primarily produced in the testes, while smaller amounts are produced in the adrenal glands.[1,2]

Testosterone belongs to a group of hormones known as androgens and contributes to a range of physiological processes throughout life.[1]

What Does Testosterone Do?

Development and Reproductive Health

During puberty, testosterone contributes to the development of male reproductive tissues and secondary sexual characteristics such as facial hair growth, voice deepening, and increased muscle mass.[1,2] It also plays an important role in sperm production and reproductive function throughout adulthood.[7]

Muscle and Bone Health

Testosterone helps regulate protein synthesis and supports the maintenance of lean muscle tissue.[2,6] It also contributes to bone mineral density, which is important for skeletal strength throughout life.[2,4]

Energy and Physical Performance

Testosterone is involved in a variety of metabolic processes and physical performance adaptations.[2,6] However, energy levels are influenced by many factors, including sleep, nutrition, physical activity, stress, and overall health.[2]

Mood and Cognitive Function

Testosterone receptors are found throughout the brain, and researchers continue to investigate the hormone's role in mood, motivation, cognition, and overall wellbeing.[2,5] These relationships are complex and influenced by numerous biological and lifestyle factors.[5]

Red Blood Cell Production

Testosterone supports erythropoiesis, the process by which red blood cells are produced, helping facilitate oxygen transport throughout the body.[2,4]

How Is Testosterone Produced?

Testosterone production is regulated by the hypothalamic-pituitary-gonadal (HPG) axis.[1,2]

This system involves communication between:

• The hypothalamus

• The pituitary gland

• The testes

The hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to release luteinising hormone (LH). LH then stimulates Leydig cells within the testes to produce testosterone.[1,7]

This process operates through a feedback mechanism that helps maintain hormone balance.[1]

Factors That Can Affect Testosterone Levels

Age

Testosterone levels generally peak during late adolescence and early adulthood and may gradually decline with age.[2,4]

Sleep Quality

Sleep is considered one of the most important lifestyle factors influencing hormone production. Testosterone production occurs predominantly during sleep, particularly during deep sleep phases.[2] Research suggests that chronic sleep restriction may be associated with reduced testosterone levels.[2]

Body Composition

Body composition may influence hormone balance. Adipose tissue contains aromatase, an enzyme that can convert testosterone into oestrogen, potentially affecting circulating hormone levels.[2,4]

Physical Activity

Regular physical activity is associated with healthy hormone function.[6] Resistance exercise has been shown to influence acute testosterone responses, although outcomes vary depending on training status, intensity, recovery, and individual factors.[6]

Stress

Chronic stress can increase cortisol production. Elevated cortisol levels may influence pathways involved in testosterone production and regulation.[2]

Nutrition

Adequate energy intake and sufficient consumption of protein, healthy fats, vitamins, and minerals support normal physiological functions, including those involved in hormone regulation.[2]

Common Myths About Testosterone

Myth 1: Higher Testosterone Always Means Better Health

Healthy hormone function depends on balance rather than maximising testosterone levels.[2,4]

Myth 2: Testosterone Only Matters for Men

Testosterone is present in both men and women and plays important physiological roles in each sex.[1,2]

Myth 3: Supplements Can Instantly Increase Testosterone

Hormone regulation is highly complex and influenced by numerous biological and lifestyle factors.[2] Sleep, nutrition, exercise, body composition, and stress management are all associated with healthy hormone function.[2,6]

Supporting Healthy Hormone Function

While testosterone levels are influenced by genetics and age, healthy lifestyle practices can support overall wellbeing and normal physiological function:[2]

• Prioritising quality sleep

• Engaging in regular exercise

• Maintaining a healthy body composition

• Managing stress

• Eating a balanced, nutrient-dense diet

• Limiting excessive alcohol intake

• Consulting a healthcare professional regarding individual health concerns

References

1. Nassar GN, Leslie SW. Physiology, Testosterone. StatPearls Publishing. Updated 2026. Available at: https://www.ncbi.nlm.nih.gov/books/NBK526128/

2. Handelsman DJ. Androgen Physiology, Pharmacology, Use and Misuse. Endotext. MDText.com, Inc.; 2020. Available at: https://www.ncbi.nlm.nih.gov/books/NBK279000/

3. McEwan IJ, Brinkmann AO. Androgen Physiology: Receptor and Metabolic Disorders. Endotext. MDText.com, Inc.; 2021. Available at: https://www.ncbi.nlm.nih.gov/books/NBK279028/

4. Bassil N, Alkaade S, Morley JE. Diagnosis and management of testosterone deficiency. Postgraduate Medicine. 2009;121(5):161-176. https://pmc.ncbi.nlm.nih.gov/articles/PMC4650468/

5. Zarrouf FA, Artz S, Griffith J, Sirbu C, Kommor M. Testosterone and Depression: Systematic Review and Meta-Analysis. Journal of Psychiatric Practice. 2009;15(4):289-305.

6. Vingren JL, Kraemer WJ, Ratamess NA, et al. Testosterone physiology in resistance exercise and training: the up-stream regulatory elements. Sports Medicine. 2010;40(12):1037-1053.

7. Walker WH. Molecular mechanisms of testosterone action on the testis. Current Opinion in Endocrine and Metabolic Research. 2019;6:29-33.