Abstract
Background: Diabetes and subclinical hypothyroidism are frequently coexisting conditions. The separated effects of each one on the cardiovascular system and cardio autonomic function are known. However, it has not been investigated yet whether the presence of both diseases has a joint influence on the cardiac autonomic system. As the autonomic nervous system is involved in cardiovascular, endocrine, and metabolic control, the association of diabetes and subclinical hypothyroidism might have combined effects, leading to cardio autonomic impairment and rising cardiovascular risk. Aim: To analyze the interaction effects of diabetes and subclinical hypothyroidism on Heart Rate Variability parameters among adults. using the participants enrolled at the baseline data of t Methods: The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a cohort of 15015 men and women aged 35 to 74 years-old recruited in 2008-10. Participants were categorized into four groups: non-diabetes with normal thyroid function (controls), non-diabetes with subclinical hypothyroidism; diabetes with normal thyroid function; and diabetes with subclinical hypothyroidism. Heart Rate Variability analyses were performed in time and frequency domains: Standard Deviation of NN interval (SDNN); Root of the Mean of the Sum of the Squares of Differences between adjacent NN intervals (RMSSD, Low-Frequency (LF) and High-Frequency (HF) on 5-minute time series collected in the supine position. For each Heart Rate Variability parameter, we divided the sample into quartile groups, using the fourth quartile as reference. We analyzed the associations with the highest quartile group for each Heart Rate Variability parameter using additive and multiplicative terms in logistic models. Results: Point Odds Ratio, and 95% Confidence Intervals (95%CI) estimates for the first quartiles of all Heart Rate Variability measures were higher for subjects with the combination of both, “diabetes plus subclinical hypothyroidism” than for people with only the diagnosis of diabetes: SDNN: 2.61 (95%CI = 1.13 to 6.05) vs. 1.52 (95%CI =1.25 to 1.85); RMSSD: 2.70 (95%CI =1.18 to 6.18) vs. 1.48 (95%CI =1.21 to 1.80); LF: 2.82 (95%CI =1.05 to 7.56) vs. 1.73 (95%CI =1.40 to 2.13); HF: 3.07 (95%CI =1.21 to 7.75) vs. 1.41 (95%CI =1.16 to 1.71). Nonetheless, no significant multiplicative interaction terms between diabetes and subclinical hypothyroidism were found for the association with HRV variables. Conclusion: There is a potential joint impact on Heart Rate Variability showed by additive effects between diabetes and subclinical hypothyroidism.
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