Table 2.

Associations Between 1976 Log₁₀ TCDD Concentration (Parts per Trillion) and Thyroid Hormone Levels by Menarcheal Status at the Time of the Explosion (1976), Seveso Women's Health Study, Italy, 1976–2009

Thyroid Hormone	No. of Participantsa	Adjustedb βc	95% CI	Menarcheal Status at Explosion						P for Interaction
				Premenarche			Postmenarche
				No.	Adjustedb βc	95% CI	No.	Adjustedb βc	95% CI
1996 Thyroid Hormone Measurements
TSHd	909	6.61	−0.87, 14.66	272	0.38	−9.34, 11.13	637	9.27	−0.76, 20.32	0.35
Total T4	889	−0.27	−0.49, −0.05	260	−0.63	−1.11, −0.15	629	−0.13	−0.37, 0.11	0.05
Free T4	894	0.01	−0.04, 0.06	260	0.02	−0.07, 0.12	634	0.01	−0.05, 0.07	0.72
Free T3	895	0.00	−0.02, 0.01	260	0.00	−0.02, 0.02	635	−0.01	−0.03, 0.02	0.70
2008 Thyroid Hormone Measurements
TSHd	722	5.44	−3.39, 15.08	225	4.82	−8.69, 20.33	497	6.41	−4.94, 19.10	0.42
Total T4	722	−0.11	−0.32, 0.12	225	0.09	−0.31, 0.48	497	−0.24	−0.48, 0.00	0.13
Free T4	724	0.00	−0.02, 0.03	225	0.01	−0.03, 0.05	499	0.00	−0.03, 0.03	0.52
Free T3	724	0.00	−0.02, 0.01	225	0.00	−0.01, 0.02	499	−0.01	−0.03, 0.01	0.30

Abbreviations: CI, confidence interval; T₃, triiodothyronine; T₄, thyroxine; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; TSH, thyroid-stimulating hormone.

^a Some participants were missing thyroid hormone measurements due to insufficient sample volume.

^b All models adjusted for age at thyroid hormone measurement and age at thyroid hormone measurement squared.

^c Coefficients represent the mean (free T₃, free T₄, and total T₄) or percent (TSH) change in thyroid hormone level for each 10-fold increase in serum TCDD concentration.

^d Percent change in serum TSH concentration was calculated using the following formula: (10^β − 1) × 100.