Cigarette smoking linked to thyroid hormone changes

Takeaway

• Cigarette smoking is associated with increased levels of free triiodothyronine (FT3) and free thyroxine (FT4) and reduced levels of thyroid-stimulating hormone (TSH), according to a cross-sectional study.

Why this matters

• The relationship between cigarette smoking and thyroid function is poorly understood, especially when adjusting for other lifestyle factors such as alcohol consumption.

Key results

• Smoking ≤20 cigarettes/day or >20 cigarettes/day were both associated with increased FT3 (P<.001 for both) and decreased TSH (P<.001 for both) in multivariate analysis.
  • Smoking ≤20 cigarettes/day was significantly associated with increased FT4 (P=.018), whereas smoking >20 cigarettes/day was not (P=.076).
• Urinary cotinine levels were correlated with FT3 (P<.001) and FT4 (P=.002), and inversely correlated with TSH (P<.001).
• Alcohol consumption >30 g/day was associated with increased TSH (P=.015) and reduced FT3 (P=.009).

Study design

• 5766 subjects with euthyroid status were analysed for smoking patterns and associations with thyroid hormone levels.
• Funding: EU Joint Programme Initiative: A Healthy Diet for a Healthy Life, the Food Biomarker Alliance.

Limitations

• Cross-sectional study design.