Normal Body Mass Index and Heart Rate Variability

Abstract

The autonomic nervous system (ANS) works in synergy with the Endocrine system that affects the body-mass and height and in turn the body mass index (BMI). The ANS activities are often assessed with one index that is heart rate variability (HRV). Reduced HRV has been reported in underweight (low BMI) and overweight (high BMI) individuals, but there is scarce information available on the relationship between normal BMI and HRV. Further, as per WHO expert consultation report, the Asian population has higher percentage of body fat than their European counterparts, therefore Asian people may have greater risk factors for type 2 diabetes and cardiovascular disease even below the existing upper edge of normal BMI. Thus it was recommended by WHO to consider the intermediate cutoff points within the normal BMI range as 18.5 Kg/m2, 20 Kg/m2, 23 Kg/m2, and 25 Kg/m2 for the Asian population. Therefore, the present study was aimed to investigate ANS activity among intermediate cutoff points of normal BMI using HRV. Seventy young individuals participated in the non-invasive and benign study. Subjects were divided into three groups based on their BMI as per the recommendation of the WHO report; NB1 (18.5<BMI≤20), NB2 (20<BMI<23) and NB3 (23<BMI<25). For all the subjects, 10 min of electrocardiogram was recorded and short term HRV analysis was carried out. Student t test was carried out to find the significance of study parameters in BMI groups. The BMI was correlated with HRV measures using Spearman’s correlation method. Statistically significant negative correlation was found between BMI and various HRV parameters. The sympathovagal balance was comparable in NB1 and NB2 group whereas it shifted towards sympathetic dominance in NB3 group. Higher sympathetic activity for BMI greater than 23 in Indian youth may lead to predictability of risks associated with overweight and obesity