Thyroid hormone levels predict the change in body weight: a prospective study.

BACKGROUND: Different studies, mostly cross-sectional, have found an association between low levels of thyroid hormones, even within the normal range, and a greater body mass index. The aim of this study was to determine the association between thyroid function and the risk for obesity. MATERIALS AND METHODS: In this population-based prospective study, measurements were made of anthropometric parameters, thyroid hormone function and urinary iodine in a cohort of the Pizarra Study (n = 937), and repeated 6 years later (n = 784). At the second point, measurements were also made of leptin and adiponectin. RESULTS: Among the persons who were not obese at the start of the study, the odds ratio (OR) of becoming obese for those in the fourth quartile (Q(4)) for free triiodothyronine (FT3) (versus those in Q(1)) was 2·94 (1·46-5·90) (P = 0·005). The OR of becoming obese in persons in Q(4) of FT4 (versus those in Q(1)) was 3·06 (1·23-7·43) (P = 0·01). Those persons in Q(4) of weight gain had a higher FT3 at the 6-year follow-up than those whose weight gain was in Q(1) (P < 0·001). Leptin correlated with thyrotropin (ß = 0·58, P = 0·001) and the FT4 (ß = -1·12, P = 0·005). Adiponectin correlated with FT3 (r = -0·24, P < 0·001). The urinary iodine correlated negatively with both the BMI (ß = -0·08, P = 0·01) and the increase in weight (ß = -0·08, P = 0·04). CONCLUSIONS: The changes in the thyroid hormones could be the consequence, rather than the cause, of the increase in weight. The same pathophysiological mechanisms that induce obesity might also be modifying the thyroid hormone pattern.

Iodine intakes of 100-300 µg/d do not modify thyroid function and have modest anti-inflammatory effects.

Little information is available as to whether doses of iodide similar to those recommended in clinical practice for the prevention of iodine deficiency in pregnant women affect thyroid function. The aim of the present study was to analyse whether doses of iodide can affect thyroid function in adults, and evaluate its effect on plasma markers of oxidative stress, inflammation and acute-phase proteins. A total of thirty healthy volunteers (ten men and twenty women) with normal thyroid function were randomly assigned to three groups (n 10). Each group received a daily dose of 100, 200 or 300 µg of iodide in the form of KI for 6 months. Free tetraiodothyronine (FT4) levels at day 60 of the study were higher in the groups treated with 200 and 300 µg (P = 0·01), and correlated with the increase in urinary iodine (r 0·50, P = 0·007). This correlation lost its significance after adjustment for the baseline FT4. The baseline urinary iodine and FT4 correlated positively with the baseline glutathione peroxidase. On day 60, urinary iodine correlated with C-reactive protein (r 0·461, P = 0·018), and free triiodothyronine correlated with IL-6 (r - 0·429, P = 0·025). On day 60, the changes produced in urinary iodine correlated significantly with the changes produced in α1-antitrypsin (r 0·475, P = 0·014) and ceruloplasmin (r 0·599, P = 0·001). The changes in thyroid-stimulating hormone correlated significantly with the changes in α1-antitrypsin (r - 0·521, P = 0·005) and ceruloplasmin (r - 0·459, P = 0·016). In conclusion, the administration of an iodide supplement between 100 and 300 µg/d did not modify thyroid function in a population with adequate iodine intake. The results also showed a slight anti-inflammatory and antioxidative action of iodide.

Iodine concentration in cow's milk and its relation with urinary iodine concentrations in the population.

BACKGROUND & AIMS: The importance of milk intake to the supply of dietary iodine is not fully known. We therefore undertook a study in Spain of the iodine concentration in cow's milk and the impact of the frequency of milk consumption on urinary iodine concentrations in three study populations. METHODS: We studied the iodine concentration in 362 samples of milk from 45 commercial brands and compared it with the milk iodine status in studies undertaken 17 years earlier. The epidemiologic studies were performed in three different places in the south of Spain: two in school-age children (N = 757 and N = 1205 children) and one in adults (N = 1051). A milk consumption questionnaire was given and urinary iodine concentrations measured. RESULTS: The mean concentration of iodine in the milk rose from 1991 (117 ± 37 µg/L) to 2008 (259 ± 58 µg/L) (P < 0.001). The iodine concentration was greater in skimmed milk (273 ± 52 µg/L) than in semi-skimmed milk (254 ± 57 µg/L) or whole milk (251 ± 61 µg/L) (P < 0.0001). The winter samples had a greater concentration of iodine (270 ± 55 µg/L) than the summer samples (247 ± 58 µg/L) (P < 0.0001), independently of the type of milk. The urinary iodine concentrations in all three epidemiologic studies were significantly associated with the frequency of milk intake. CONCLUSIONS: The concentration of iodine in cow's milk has risen over recent years, and it is higher in skimmed milk. The results also show that cow's milk is a relevant source of dietary iodine.

Effect of iodine prophylaxis during pregnancy on neurocognitive development of children during the first two years of life.

CONTEXT: The association between thyroid function during pregnancy and the later mental and psychomotor development of the child is supported by numerous experimental, clinical, and epidemiological studies. OBJECTIVE: The aim of the study was to evaluate the psychological development of infants aged 3 to 18 months whose mothers had received 300 microg of potassium iodide during the first trimester of their pregnancy and compare with infants whose mothers had received no iodine supplements. DESIGN AND STUDY SUBJECTS: The study included 133 women who had received 300 microg of potassium iodine and 61 women who had received no iodine supplements. MAIN OUTCOME MEASURES: The neuropsychological status of the children was evaluated with the Bayley Scales of Infant Development, and measurements were made of TSH, free T(3), free T(4), and urinary iodine. RESULTS: Those children whose mothers had received an iodine supplement of 300 microg had a more favorable psychometric assessment than those of the other group of mothers. They had higher scores on the Psychomotor Development Index (P = 0.02) and the Behavior Rating Scale. CONCLUSIONS: Dietary iodine supplements not only have no harmful effect on the neurodevelopment of the children, they may even be beneficial. Given the possible presence of confounding variables not controlled for in this study, these findings should be considered as preliminary.