Can decreased heart rate variability be a marker of autonomic dysfunction, metabolic syndrome and diabetes?

Epidemiological studies show an emergence of diet- and lifestyle-related diseases; Cardio-metabolic diseases (CMD) and neuropsychiatric diseases (classified as non-communicable diseases or chronic diseases). Diet and lifestyle factors can cause adverse effects on autonomic function resulting in decreased heart rate variability (HRV). Low HRV is a risk factor for CMDs. There is a need to find out new methods of early diagnosis for prevention and treatment of these problems because the neurohormonal dysfunction could be the earliest manifestation. It is possible that HRV could be a marker for the early diagnosis of these problems, because it is characterised with increased sympathetic and reduced parasympathetic activity. Several studies indicate that increased unhealthy diet, mental stress, sedentary lifestyle, tobacco, insomnia and alcoholism may be associated with neurohormonal dysfunction, which may cause decline in HRV. Majority of the chronic diseases (e.g., diabetes, hypertension, heart attack, neuropsychiatric disease and cancer) are associated with decreased HRV. The studies also indicate that solar and geomagnetic activities may influence circadian clock and hypothalamus resulting in the oxidative stress and inflammation with alteration in HRV. It is possible that reduced HRV will correlate with various stages of autonomic dysfunction, associated with chronic diseases. Simple methods need to be developed to measure HRV for early diagnosis of neurohormonal dysfunction, which may be important for early management. This review aims to find out available evidence on the role of HRV in the early diagnosis of chronic disease (with specific focus on Type 2 diabetes) and the factors affecting HRV.