Age- and gender-dependent urinary iodine concentrations in an area-covering population sample from the Bernese region in Switzerland

Abstract

Objective: Before a scheduled increase of salt iodide content up to 20 p.p.m, in Switzerland, urinary iodine concentration (UIC, μg/l) of a randomly selected, area-covering, age-stratified population subgroup was sampled in spring 1997. In contrast to former published studies on UIC, we minimized biases by age, gender, rural/urban, socio-economic and cultural influences. Methods: We contacted 750 households in the Bernese region using random telephone numbers. Per household, one proband selected by play dice collected a spot urine sample. We defined seven age categories: infants, children, adolescents, adults I-III and seniors, aged 0-5, 6-12, 13-20, 21-35, 36-50, 51-65 and >65 years respectively. Randomized UIC data were compared with WHO criteria of iodine deficiency (IB) and previous non-randomized, age-dependent Swiss UIC data. To recruit a perfect random group of volunteers proved difficult, as study participation of adolescent and male populations was somewhat lower than that of elder and female (P < 0.005) populations respectively. Study participation of inhabitants of rural and suburban regions was comparable (P = 0. 139). Out of 413 obtained urine spots, 412 (55%) were analyzed statistically (58% women, 42% men, P < 0.005). Results: Ninety per cent of all UIC values ranged between 25 and 200 μg/l. Median UIC showed mild ID (94 μg/1). UIC varied significantly between age categories (P = 0.0006). Women had lower UIC than men (P = 0.014). Infants had no ID. Women in child-bearing age (13-35 years), adults II, adults III and seniors had mild ID. Compared with recommended supplies of 150 and 200 μg I/day in children and male adolescents respectively, we consider their UIC (110 and 144 μg/l) as at least borderline deficient. Absolute UIC was lowest in seniors. Probands from rural/suburban households had similar UICs. Our UIC data were comparable to published ones. Conclusions: Despite long-term national efforts with iodized salt (15 p.p.m. in 1997), mild ID still prevailed in Bern in spring 1997, with rare extreme UIC values. Mild ID with women in child-bearing age (and probably also with children and male adolescents) was a serious concern, as goiter growth with puberty or pregnancy might be the consequence. Mild ID in adults and seniors might be due to restricted NaCl intake. Results of our randomly selected subgroup from a 650 000 population show that age- and gender-dependency are important when comparing our collected data with published UIC data. This fact must be considered with non-randomly selected population subgroups.