Nov 06

Heart rate variability: an objective measure of health

Heart rate variability (HRV) is the variation in time between consecutive heartbeats. Each time our heart beats, there is a variation in time between each beat. It does not (or should not) beat in a consistent rhythm. In fact, research shows that a higher HRV is associated with better health.

HRV is a measure of the responsiveness of our autonomic nervous system (ANS). The ANS is a part of our peripheral nervous system that regulates involuntary physiological processes such as our heart rate, blood pressure, breathing, and digestion. More specifically, HRV is a measure of the balance between two parts of our ANS; the parasympathetic and sympathetic nervous systems [1].

Our sympathetic nervous system (SNS) is associated with our “fight or flight” response. This is a state of increased activity comprising increases in blood pressure, heart rate, and glucose production, and a slowing in our digestion. Activation of our parasympathetic nervous system (PNS) is associated with “rest and digestion” comprising a slowing in our heart rate, decrease in blood pressure, and an increase in certain digestive processes. The balance between our SNS and PNS is important. Overactivity in one of these systems can impair both mental and physical health. Unfortunately, for many people, particularly those with depression and anxiety, there is an overdominance in the SNS. As stated earlier, HRV is a measure of the balance between our PNS and SNS. A higher HRV, which is associated with an increased PNS is a marker of good health. A higher HRV is also a marker of increased activity in our vagus nerve. This is our longest cranial nerve that is connected to our gut, liver, heart, and lungs. Increasing the activity of our vagus nerve is associated with improvements in many physical and mental conditions. For example, vagus nerve stimulation is an effective treatment for epilepsy, treatment-resistant depression, and migraine [2].

There is increasing research suggesting HRV can be used as an objective measure of health. HRV tends to decrease as we age, is higher in fitter people, and those living a healthier lifestyle. HRV is also strongly correlated with levels of inflammation in the body. In people with cardiovascular disease or people who have experienced a myocardial infarction, a lower HRV is associated with an increased risk of mortality. HRV is also lower in people with depression, post-traumatic stress disorder, burnout syndrome, and is lowered during times of stress. People with higher HRV have been shown to have a better cancer prognosis and disease progression. Overall, HRV can be an objective measure of stress [4-8].

HRV is traditionally measured using an electrocardiogram (EEG). However, there are devices on the market that can also measure HRV with varying levels of reliability. These include finger sensors and Polar chest straps. There are also apps on our phone and watches that can also measure HRV, although the reliability of these is disputed. Devices such as HeartMath are specifically designed to measure HRV. Heartmath is an intervention that teaches people ways (through controlled breathing) to increase HRV.

Here are some natural ways to increase HRV/ Vagus nerve activity

  • Slow, controlled breathing
  • Relaxation practice
  • Biofeedback
  • Meditation
  • Yoga
  • Massage
  • Exercise and increasing overall fitness
  • Eating a healthier diet. The foods we eat can affect HRV and generally eating a healthier diet (e.g., Mediterranean diet) can increase HRV. Fasting and caloric restriction can affect HRV [9,10]
  • Increase omega-3 polyunsaturated acids (e.g., fish oils) [11]
  • Ensure good vitamin and mineral status. There is some research showing low vitamin D, vitamin B12, magnesium, and iron are associated with lower HRV [12-15]
  • Probiotics. This has been shown in animal studies but no human studies so far [16]
  • Herbs/spices such as curcumin and saffron [17-18]
  • Listening to music particularly classical music
  • Laughing
  • Gargling and triggering your gag reflex. However, I am not convinced by the long-term effects of these and how many people can (or are) willing to do these regularly.

Given the association between HRV and improved mental and physical health, implementing ways to increase it are likely important. More research needs to be conducted in the area but HRV also presents as a promising objective measure of health.

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References

  1. Kemp, A.H., Koenig, J., Thayer, J.F., 2017. From psychological moments to mortality: A multidisciplinary synthesis on heart rate variability spanning the continuum of time. Neurosci Biobehav Rev 83, 547-567.
  2. Johnson RL and Wilson CG. A review of vagus nerve stimulation as a therapeutic intervention. J Inflamm Res. 2018 May 16;11:203-213.
  3. Shaffer, F., McCraty, R., Zerr, C.L., 2014. A healthy heart is not a metronome: an integrative review of the heart’s anatomy and heart rate variability. Front Psychol 5, 1040.
  4. Jandackova, V.K., Scholes, S., Britton, A., Steptoe, A., 2019. Healthy Lifestyle and Cardiac Vagal Modulation Over 10 Years: Whitehall II Cohort Study. J Am Heart Assoc 8, e012420.
  5. Sessa, F., et al. 2018. Heart rate variability as predictive factor for sudden cardiac death. Aging (Albany NY) 10, 166-177.
  6. Kim, H.G., Cheon, E.J., Bai, D.S., Lee, Y.H., Koo, B.H., 2018. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature. Psychiatry Investig 15, 235-245.
  7. Koch, C., Wilhelm, M., Salzmann, S., Rief, W., Euteneuer, F., 2019. A meta-analysis of heart rate variability in major depression. Psychol Med 49, 1948-1957.
  8. Kloter, E., Barrueto, K., Klein, S.D., Scholkmann, F., Wolf, U., 2018. Heart Rate Variability as a Prognostic Factor for Cancer Survival – A Systematic Review. Front Physiol 9, 623.
  9. Mzoughi, K., Zairi, I., Jabeur, M., Kraiem, S., 2018. The effects of fasting on heart rate variability in hypertensive patients. Clin Exp Hypertens 40, 793-796.
  10. Nicoll, R., Henein, M.Y., 2018. Caloric Restriction and Its Effect on Blood Pressure, Heart Rate Variability and Arterial Stiffness and Dilatation: A Review of the Evidence. Int J Mol Sci 19.
  11. Christensen, J.H., 2011. Omega-3 polyunsaturated Fatty acids and heart rate variability. Front Physiol 2, 84.
  12. Aytemir, K., et al., 2000. Assessment of autonomic nervous system functions in patients with vitamin B12 deficiency by power spectral analysis of heart rate variability. Pacing Clin Electrophysiol 23, 975-978.
  13. Brilla, L., Teichler, L., Hahn, T., Freeman, J., Li, Y., 2010. Effect of Magnesium on Heart Rate Variability in Healthy Subjects. FASEB Journal 24, 1.
  14. Canpolat, U., et al. 2015. Impaired cardiac autonomic functions in apparently healthy subjects with vitamin D deficiency. Ann Noninvasive Electrocardiol 20, 378-385.
  15. Tuncer, M., et al. 2009. Heart rate variability in patients with iron deficiency anemia. Arq Bras Cardiol 92, 368-371, 385-368, 400-363.
  16. Bercik, P., et al., 2011. The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut-brain communication. Neurogastroenterol Motil 23, 1132-1139.
  17. Joukar, S., Dehesh, M.M., 2015. The safety assessment of saffron (Crocus sativus L.) on sympathovagal balance and heart rate variability; a comparison with amiodarone. Auton Autacoid Pharmacol 35, 46-50.
  18. Thephinlap, et al., 2011. Reversal of cardiac iron loading and dysfunction in thalassemic mice by curcuminoids. Med Chem 7, 62-69.
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