Thyroid function and serum ferritin levels: the study of health in Pomerania

Association between thyroid function and assessment of hepatic fat and iron contents by magnetic resonance imaging

The associations of thyroid function parameters with non-alcoholic fatty liver disease (NAFLD) and hepatic iron overload are not entirely clear. We have cross-sectionally investigated these associations among 2734 participants of two population-based cross-sectional studies of the Study of Health in Pomerania. Serum levels of thyroid-stimulating hormone (TSH), free tri-iodothyronine (fT3), and free thyroxine (fT4) levels were measured. Liver fat content (by proton-density fat fraction) as well as hepatic iron content (by transverse relaxation rate; R2*) were assessed by quantitative MRI. Thyroid function parameters were associated with hepatic fat and iron contents by median and logistic regression models adjusted for confounding. There were no associations between serum TSH levels and liver fat content, NAFLD, or hepatic iron overload. Serum fT4 levels were inversely associated with liver fat content, NAFLD, hepatic iron contents, and hepatic iron overload. Serum fT3 levels as well as the fT3 to fT4 ratio were positively associated with hepatic fat, NAFLD, hepatic iron contents, but not with hepatic iron overload. Associations between fT3 levels and liver fat content were strongest in obese individuals, in which we also observed an inverse association between TSH levels and NAFLD. These findings might be the result of a higher conversion of fT4 to the biologically active form fT3. Our results suggest that a subclinical hyperthyroid state may be associated with NAFLD, particularly in obese individuals. Furthermore, thyroid hormone levels seem to be more strongly associated with increased liver fat content compared to hepatic iron content.

Micronutrients, iodine status and concentrations of thyroid hormones: a systematic review

Context

The metabolism of thyroid hormones, which are essential for normal development, involves many proteins and enzymes. It requires iodine as a key component but is also influenced by several other micronutrients, including selenium, zinc, iron, and vitamin A.

Objective

This systematic review was designed to investigate the effect of micronutrient status and supplementation on iodine status and thyroid hormone concentrations.

Data Sources

Using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines, electronic databases were searched from their inception to April 2016.

Study Selection

Human studies published in English and reporting data on micronutrient status and iodine status and/or thyroid hormone concentrations were included. Studies that examined the effect of micronutrient supplementation on iodine status and/or thyroid hormone concentrations were also included.

Data Extraction

A predesigned and piloted data extraction form was used to compile data from individual studies.

Results

A total of 57 studies were included: 20 intervention studies and 37 observational studies. Although observational evidence suggests that concentrations of selenium, zinc, and iron are positively associated with iodine status, data from randomized controlled trials fail to confirm this relationship.

Conclusions

Further studies are needed to provide greater understanding of the role of micronutrient status in iodine nutrition and thyroid function to ascertain the public health implications for populations worldwide.

Coexisting micronutrient deficiencies among Sri Lankan pre-school children: a community-based study

Assessing micronutrient status in children may also have the benefit of addressing the problems of various micronutrient deficiencies with a unified programmatic approach on a public health scale. A cross-sectional survey in the Galle district of the micronutrient and anthropometric status of 248 children of ages 3-5 years was performed to determine the prevalence of micronutrient deficiencies [iron, zinc (Zn), folate, calcium, caeruloplasmin, iodine, vitamin A and vitamin D] and the extent to which multiple micronutrient deficiencies coexist. The prevalence of anaemia [haemogbolin (Hb) < 110.0 g L⁻¹] was 34.0% in males and 33.0% in females (overall 33.5%, gender difference, P = 0.92). In anaemic children, 7.0% of males and 15.0% of females were iron deficient (serum ferritin < 15.0 µg L⁻¹). Folate deficiency (<3.00 ng mL⁻¹) was found in 41.0% and 33.0% of male and female, respectively, whereas Zn deficiency (<9.95 µmol L⁻¹) occurred in 57.0% and 50.0% of male and female, respectively. Serum vitamin D deficiency (<35.0 nmol L⁻¹) was found in 26% and 25% of male and female, respectively. Anaemic males had a 3.0-fold (95% confidence interval (CI) 1.1-8.3) and 2.3-fold (95% CI 0.8-6.6) greater risk of being underweight and thin, whereas the risk among anaemic females was 0.7-fold (95% CI 0.3-1.8) and 0.9-fold (95% CI 0.3-2.6) for being underweight and thin. Only 7.3% of the subjects did not have any micronutrient deficiency, 38.3% were deficient in two micronutrients, 17.7% had three micronutrient deficiencies and 6.0% had four or more micronutrient deficiencies. Multiple micronutrient deficiencies are prevalent in Sri Lankan pre-school children and established baseline data for future studies.

Significant association between thyroid hormones and erythrocyte indices in euthyroid subjects

OBJECTIVE

Hypothyroidism and hyperthyroidism are each associated with anaemia, but relationships between thyroid function and erythrocyte indices in euthyroid subjects have not been examined. The aim of this study was to examine these relationships in a community-based cohort.

DESIGN, SUBJECTS AND MEASUREMENTS

Linear regression models with free T4, free T3 and TSH as predictors of erythrocyte indices and serum iron parameters were fitted to data from a cohort of 1179 participants in the 1994 Busselton health study and a subset of 1011 euthyroid participants. All models were adjusted for age, age(2), sex and an age-sex interaction.

RESULTS

In the full cohort and euthyroid subset, there were significant, positive linear relationships between free T4 and each of haemoglobin, haematocrit and erythrocyte count (P < 0·01 for each), such that in euthyroid participants, each 1·0 pM increase in free T4 was associated with an increase in haemoglobin of 0·39 g/l. There were significant relationships between free T3 and each of haemoglobin, haematocrit and erythrocyte count (P < 0·001 for each), with the best model fits obtained using free T3(2), indicating curved relationships. TSH had a significant (P < 0·05) inverse relationship with serum iron and transferrin saturation in the full cohort and the euthyroid subset. Serum iron concentrations were lower in participants with subclinical hypothyroidism (n = 87) than euthyroid subjects [mean (SD) 15·9 (4·7) vs 18·4 (6·0) μM, P = 0·001].

CONCLUSION

In euthyroid subjects, small differences in thyroid function are associated with significant differences in erythrocyte indices.