Can smoking reduce testosterone levels?

Effect of Smoking on Testosterone Levels

Contrary to what might be expected, smoking is associated with increased rather than decreased testosterone levels in men, with smokers having approximately 15% higher total testosterone and 13% higher free testosterone compared to non-smokers.

Evidence on Smoking and Testosterone

Impact on Testosterone Levels

• Multiple studies consistently show that smoking is associated with higher, not lower, testosterone levels in men:

  • A meta-analysis of 22 studies involving 13,317 men found smokers had significantly higher mean testosterone levels than non-smokers (1.53 nmol/L higher) 1
  • The Tromsø study of 3,427 men demonstrated that smoking men had 15% higher total and 13% higher free testosterone levels compared to non-smokers 2
  • Several studies reported increased serum testosterone in smokers compared to non-smokers 3

• The effect appears to be dose-dependent:

  • Total and free testosterone levels increase significantly with increasing number of cigarettes smoked daily 2
  • However, some research indicates a negative correlation between testosterone levels and the amount of tobacco exposure over time 4

Mechanisms and Bioavailable Testosterone

• While total and free testosterone are elevated in smokers, bioavailable testosterone (the fraction not bound to sex hormone-binding globulin) may not be significantly affected:

  • One study found no significant differences in bioavailable testosterone between smokers and non-smokers (3.78 vs 3.51 nM, P=0.49) 5
  • The elevation in total testosterone may be partly explained by changes in sex hormone-binding globulin (SHBG) levels 5

• At the cellular level, nicotine exposure can actually decrease testosterone production in Leydig cells through autophagy rather than apoptosis:

  • Nicotine exposure upregulates autophagy-related genes like Beclin1 and LC3 6
  • This process is mediated through the TCL1-mTOR-autophagy signaling pathway 6

Clinical Implications

• Smoking may mask borderline hypogonadism by artificially elevating testosterone levels 2

  • This could potentially delay diagnosis and treatment of testosterone deficiency

• For men with low testosterone symptoms being evaluated for testosterone therapy:

  • Smoking status should be considered when interpreting testosterone levels
  • Guidelines recommend measuring testosterone on at least two separate morning occasions to confirm hypogonadism 7
  • Target testosterone levels during treatment should be in the mid-normal range (350-600 ng/dL) 7

• For men trying to conceive:

  • Smoking has negative effects on semen quality and male fertility despite the higher testosterone levels 3
  • WHO guidelines strongly recommend that men trying for pregnancy should abstain from smoking 3

Conclusion

The evidence clearly shows that smoking is associated with higher, not lower, testosterone levels in men. However, this does not translate to better reproductive health or hormonal function. The elevated testosterone in smokers may be clinically misleading and could mask underlying hypogonadism. Given smoking's numerous negative health effects, including potential negative impacts on male fertility, smoking cessation remains an important recommendation regardless of its effects on testosterone levels.