Thyroid hormones and erythrocyte indices in a cohort of euthyroid older subjects.

OBJECTIVES: Hypothyroidism is associated with normocytic anaemia. Indeed, a limited number of studies have shown significant associations between free thyroxin (T4) and erythrocyte indices. These studies did not include vitamin B12, folic acid, iron and renal function in the analyses. We therefore studied the association between thyroid hormones and erythrocyte indices in a population-based cohort of older euthyroid subjects, with adjustment for major confounding parameters. DESIGN: Data, including thyroid hormones and erythrocyte indices, are from the Longitudinal Aging Study Amsterdam (LASA), an ongoing cohort study on predictors and consequences of changes in health in the ageing population in the Netherlands. Multivariable linear regression analyses were applied to study the cross-sectional associations between free T4, thyroid stimulating hormone (TSH) and erythrocyte indices (haemoglobin content, haematocrit, mean cell volume (MCV) and erythrocyte count) in a euthyroid sub-sample. The final models were adjusted for vitamin B12, folic acid, iron levels and renal function. RESULTS: In 708 euthyroid older subjects, an increase of 5pmol/L free T4 was associated with a mean increase of 0.12mmol/L or 0.19g/dL of haemoglobin, 0.068 10(12)/L erythrocytes and 0.006L/L haematocrit (P=0.007, P=0.005, P=0.001, respectively). Free T4 was not significantly associated with MCV (P>0.05). TSH appeared not to be associated with any of the erythrocyte indices (all P>0.05). CONCLUSIONS: In a cohort of older subjects, free T4, but not TSH, was associated with erythrocyte indices, confirming the role of thyroid hormones in the regulation of erythropoiesis.

Thyroid function and the metabolic syndrome in older persons: a population-based study.

BACKGROUND: Studies suggest an association between a high TSH and (individual components of) the metabolic syndrome. Only a few studies have been performed in the general older population. OBJECTIVE: This study investigates the association between serum TSH and the metabolic syndrome in a representative sample of older persons in The Netherlands. DESIGN AND PATIENTS: Data of the Longitudinal Aging Study Amsterdam were used, which is an ongoing cohort study in a representative sample of Dutch older persons. A total of 1187 subjects (590 men and 597 women) between the ages of 65 and 88 years participated in the study. MEASUREMENTS: Metabolic syndrome (US National Cholesterol Education Program definition) and its individual components were assessed, as well as serum TSH levels. RESULTS: Among the participants, the prevalence of the metabolic syndrome was 34.2%. The mean serum TSH was 1.9 mU/l. Subjects in the upper quartile with a serum TSH level above 2.28 mU/l (odds ratio (OR)=1.68; 95% confidence interval (CI) 1.19-2.37) had a significantly increased prevalence of metabolic syndrome compared with subjects in the lowest quartile with a serum TSH below 1.04 mU/l. After adjustment for confounders, age, sex, alcohol use, total physical activity, and smoking, the OR was 1.62 (95% CI 1.15-2.32). CONCLUSIONS: Subjects with a serum TSH in the upper quartile have a higher prevalence of metabolic syndrome as compared with subjects with a serum TSH in the lowest quartile.