Metabolic syndrome (MetS) is a major global health concern characterized by a cluster of interrelated risk factors—abdominal obesity, hyperglycemia, dyslipidemia, and hypertension—that together increase cardiovascular morbidity and mortality1. The prevalence of MetS has been steadily increasing even among younger populations, largely attributed to sedentary lifestyles, dietary excess, and psychosocial stress2. Detecting subclinical autonomic imbalance before overt metabolic abnormalities develop could be pivotal in preventive cardiometabolic strategies3.

Heart rate variability (HRV) represents beat-to-beat fluctuations in cardiac intervals and serves as a sensitive index of autonomic nervous system (ANS) modulation of the heart4. Decreased HRV reflects sympathetic predominance and reduced parasympathetic tone, which are known precursors of metabolic and cardiovascular dysregulation5. HRV assessment is simple, non-invasive, and reproducible—making it a potentially valuable tool for early detection of autonomic dysfunction in at-risk populations6.

Previous studies have demonstrated reduced HRV in obese and diabetic individuals7, but evidence in young adults without overt disease remains limited. Considering that autonomic imbalance may precede insulin resistance and vascular endothelial dysfunction8, assessing HRV among young adults could provide an early biomarker for metabolic syndrome development9.

This study aims to evaluate HRV parameters in young adults with and without metabolic syndrome and to establish correlations with individual metabolic components. By focusing on a relatively young population, this research attempts to elucidate the role of HRV as an early, non-invasive predictor of metabolic derangement—thereby aiding early identification and intervention.

A prospective, observational study was conducted among 160 young adults (18–35 years) attending the health screening unit of a tertiary medical college between January and December 2024. Ethical clearance was obtained prior to initiation.

Inclusion Criteria

• Age 18–35 years
• Willingness to participate with informed consent
• For MetS group: fulfilling ≥3 IDF (2005) criteria for metabolic syndrome:
• Waist circumference ≥90 cm (men) or ≥80 cm (women)
• Fasting glucose ≥100 mg/dL
• Triglycerides ≥150 mg/dL
• HDL cholesterol <40 mg/dL (men) or <50 mg/dL (women)
• Blood pressure ≥130/85 mmHg

Exclusion Criteria

• History of cardiovascular, endocrine, or neurological disorders
• Alcohol or tobacco use
• Medications affecting HRV (β-blockers, antidepressants)
• Acute illness or febrile condition

Methodology

After overnight fasting, anthropometric parameters (height, weight, BMI, waist circumference) were recorded. Blood samples were analyzed for fasting glucose and lipid profile using standard enzymatic methods. Resting blood pressure was measured using a calibrated sphygmomanometer.

HRV was assessed using a 5-minute lead II ECG under standardized conditions. Time-domain parameters (mean RR, SDNN, RMSSD) and frequency-domain measures (LF, HF, LF/HF ratio) were calculated using Kubios HRV software.

Statistical Analysis

All data were analyzed using SPSS v26. Continuous variables were expressed as mean ± SD. Comparisons between groups were made using independent t-tests. Pearson’s correlation was used to assess associations between HRV indices and metabolic parameters. p < 0.05 was considered statistically significant.

Table 1. Demographic Characteristics

Table 2. Metabolic Parameters

Table 3. Time Domain HRV Parameters

Table 4. Frequency Domain HRV Parameters

Table 5. Correlation Between HRV and Metabolic Components

(*p < 0.05, *p < 0.01)

Table 6. Logistic Regression Predicting MetS

The present study demonstrates significant autonomic dysfunction, reflected by reduced HRV, among young adults with metabolic syndrome. Both time- and frequency-domain parameters were markedly deranged, indicating reduced vagal tone and increased sympathetic activity. These findings support the hypothesis that autonomic imbalance precedes metabolic and vascular alterations10.

Comparable reductions in HRV have been reported by Thayer et al.11 and Shaffer & Ginsberg12, who emphasized HRV as a biomarker for cardiometabolic health. Our results align with Singh et al.13, who observed decreased parasympathetic modulation in overweight young adults. Similar studies by Fatouleh et al.14 and Narkiewicz et al.15 corroborate that early autonomic dysfunction may initiate a cascade leading to insulin resistance and hypertension.

The strong inverse correlation between HRV indices and waist circumference or fasting glucose in our study suggests that visceral adiposity and hyperglycemia directly impair autonomic regulation. The elevated LF/HF ratio implies sympathetic overdrive—a well-recognized mechanism contributing to endothelial dysfunction and pro-inflammatory states16.

Early recognition of such changes in young individuals provides an opportunity for preventive strategies emphasizing weight control, exercise, and stress reduction. Interventional trials have shown that lifestyle modification can restore HRV and improve insulin sensitivity17.

Limitations include single-center design and short ECG recording duration. Longitudinal follow-up could confirm causality. Nevertheless, the robust associations highlight HRV as a reliable, low-cost, non-invasive screening biomarker in young populations vulnerable to future metabolic and cardiovascular disorders.

Reduced HRV parameters in young adults with metabolic syndrome signify early autonomic dysfunction. HRV assessment may thus serve as an effective non-invasive tool for identifying individuals at risk for developing MetS and cardiovascular diseases. Integrating HRV analysis into routine health screening could facilitate early intervention and long-term risk reduction.

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