Pilot study of urinary iodine concentration and of biochemical thyroid parameters before and after cautious public health intervention on salt iodide content: The Swiss longitudinal 1996-2000 iodine study

Objective and design: Iodide concentration (IC) in salt was cautiously increased in Switzerland (15-->20 ppm iodide). We evaluated the dynamics of the effect of this intervention on urinary iodine concentration (UIC, mug/l) and on thyroid parameters. Setting: University Hospital in Bern, Switzerland. Subjects: A cohort of 36 subjects ( 12 children, 11 women, 13 men) out of 44 were recruited. Interventions: During the study periods PRE (May 1996-May 1998) and POST (October 1998-December 2000, subdivided into equal subperiods POST1 and POST2), that is, before and after the increase of IC in salt, subjects collected 6248 urine spots for analysis of UIC. Thyroid volumes (n = 2/subject) and serum thyroid parameters (n = 8/subject) were sequentially evaluated. Methods: Average PRE-POST data were compared ( multiple regression analysis). Results: UIC increased overall by 5.1% (P = 0.0003). Increase of UIC was highest in children (11.3%, P<0.0001), significant in women (8%, P = 0.0016), but not significant in men (P = 0.143). Comparison between periods POST1 and POST2 showed that UIC changed more gradually in women than in children. Thyroid volumes were normal, no nonphysiological change occurred. TSH indicated euthyroidism; it decreased in children (1.98 double right arrow 1.74 mU/l, P = 0.04) and increased in men (1.65 double right arrow 1.91mU/l, P = 0.025). FT3 decreased in children (P<0.004) and FT4 decreased in men (P = 0.017), both within normal ranges. TSH, FT3 and FT4 were unchanged in women. FT3/FT4 ratios were stable. Anti-TPO-Ab titers were stable (P = 0.9). Anti-Tg-Ab titers decreased (P = 0.009). Conclusion: The significant UIC effects were of uncertain metabolic relevance. No pathological side effects occurred. Differential delays and penetrances of UIC increase in children and adults were hitherto unknown. The unspectacular stepwise policy seems to be safe. Our pilot results in a population with moderate iodine deficiency in women should be confirmed in population-based cluster studies.