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Heart rate variability, or the ability of the heart to quickly change how rapidly it beats in order to meet the body’s energy needs, is an important indicator of heart health. Researchers recently evaluated whether type 2 diabetes influences heart rate variability.
The heart needs to constantly vary the rate at which it beats in order for the body to respond optimally to its current situation. This is most obvious when performing strenuous exercise, but smaller adjustments to heart rate are needed to react to the constant subtle changes in the environment. Having a high heart rate variability is a sign of good cardiovascular health. In contrast, people with low variability in heart rate are at increased risk of developing heart disease.
Type 2 diabetes can damage the nerves leading to the heart
Heart rate is controlled by the autonomic nervous system, which is responsible for bodily functions that we can’t consciously control. Part of the autonomic nervous system reacts to stressful situations by stimulating the heart rate, preparing for a potential emergency “fight-or-flight” response. Another part of the nervous system slows down the heart in more relaxed situations. Type 2 diabetes, a common disease among older adults, can damage the nerves that lead to the heart. This could potentially impair the ability of the autonomic nervous system to control heart rate.
Conflicting results from previous studies
Previous studies on heart rate variability in diabetics have yielded conflicting results, with some studies finding evidence of lower heart variability in diabetic patients, whereas other studies did not find an effect. Researchers from France set out to combine and re-analyze the results from all of these previous studies in order to determine if type 2 diabetes is associated with changes to heart rate variability. The results were recently published in the journal PLOS ONE.
The researchers searched for studies that had compared heart rate variability between non-diabetics and patients with type 2 diabetes. The studies had to have measured heart rate variability over a 24-hour period using electrocardiography. This technique uses electrodes on the skin to measure the weak electrical pulses emitted by the heart when it beats and is considered to be the best method for measuring heart rate variability. More variation in the duration between beats indicates higher variability. Variability can also be interpreted with different mathematical models that allow researchers to differentiate between the stimulatory and relaxing aspects of the nervous system.
The researchers were able to find 25 published studies that met their criteria. The studies included 2,932 participants in total, with the individual studies including anywhere from 12 to 457 people in their diabetic or non-diabetic groups. The average age for diabetic participants was 58 years, and 56 years for non-diabetics. The participants were evenly split between male and female.
Patients with type 2 diabetes have lower heart rate variability
Most studies found that diabetics had lower heart rate variability or at least a trend towards lower variability. When considering all the studies together, heart rate variability was clearly decreased in the diabetics. The researchers found that both stimulatory and calming aspects of the autonomic nervous system on the heart were less effective in diabetic patients than in non-diabetics.
The researchers pointed out that this study had some limitations. Notably, the different studies that they combined for their analysis had a wide range of objectives and patient groups. For example, in some studies both diabetic and control patients had cardiovascular or kidney disease, whereas in others they had no other health conditions. Some studies didn’t even describe the health status of their non-diabetic control groups.
Overall, this study provides strong evidence that heart rate variability is decreased in people with type 2 diabetes. Since lower heart rate variability is associated with an increased risk of heart failure, the researchers suggest that this is something that should be routinely evaluated in diabetic patients.
Written by Bryan Hughes, PhD
Reference: Benichou, T., Pereira, B., Mermillod, M., Tauveron, I., Pfabigan, D., Maqdasy, S. & Dutheil, F. Heart rate variability in type 2 diabetes mellitus: A systematic review and meta–analysis. PLOS ONE 13, e0195166 (2018)