Diabetes and subclinical hypothyroidism on heart rate variability

BACKGROUND To analyze the interaction effects between diabetes and subclinical hypothyroidism with respect to heart rate variability parameters, using baseline data from the Brazilian Longitudinal Study of Adult Health. MATERIALS AND METHODS The subsample was categorized into four groups: subjects without diabetes and normal thyroid function (controls); subjects without diabetes and subclinical hypothyroidism; patients with diabetes and normal thyroid function; and patients with diabetes and subclinical hypothyroidism. Heart rate variability analyses were performed by linear time and frequency domain analyses in 5-minute time series collected in the supine position. The associations were then analyzed, with the lowest quartile group for heart rate (HR) and the highest quartile group for each heart rate variability parameter using additive and multiplicative terms in logistic models. RESULTS Point odds ratio estimates for the 4th quartiles of heart rate and 1st quartiles of all heart rate variability measurements were higher for subjects with combined diabetes and subclinical hypothyroidism than for diabetes only, independently of main sociodemographic and clinical variables (HR: 8.33 vs. 2.63; SDNN: 2.59 vs. 1.61; RMSSD: 2.37 vs. 1.42; LF: 2.83 vs. 1.71; HF: 3.06 vs. 1.39), but not independently of HbA1c and TSH. Only the interaction term for the association with heart rate, adjusted for sociodemographic and clinical variables, had borderline statistical significance. CONCLUSION Diabetes and subclinical hypothyroidism exert a potential joint impact on cardiac autonomic control, showed by additive effects between DM and SCH, as well as a significant interaction term for the association with heart rate.