Low heart rate variability (HRV) s associated with reduced lifespan, cardiovascular diseases (CVD), diabetes, several mental health diseases and a growing list of other conditions I will cover in this post. For a more thorough background check out my two previous posts: heart measurements for your health , what heart rate measurements can tell you about your brain.
Heart rate variability can be broken into time and frequency. Regarding time, though there are still many measurements of this, you can think of one as the standard deviation between interbeat intervals (IBI). As for frequency: both low frequency and high frequency spectral power have been used an indices of vagal activity.
Another way to look at these two measurement of variability is that frequency domains are an attempt to try to dissect out the excitatory (sympathetic) and inhibitory (parasympathetic) components/contributions, while the time series measurements are seeking to measure the overall chaos or complexity in the system.
As for the general take home message, people with a higher rate of variability are considered healthier and less likely to die. So at first this might sound somewhat counterintuitive for those not familiar to the heart field or chaos theory. But think of it as the more dynamic the system the better it can react to external changes.
Overall: low heart rate variability is bad and related to several diseases and predictive of a shorter lifespan. The other thing to keep in mind is that the higher the sympathetic drive the lower the HRV (sympathetic is one component of the autonomic nervous system - the other being the parasympathetic). Enough of the background (for more check my previous post listed above).
What are some of the other conditions that are related to decreased HRV? One could guess any overall negative health condition may lower HRV. Obesity would be one example and research has found that these individuals do have a lower HRV (Piestrzeniewicz et al., 2008). Subjects with a BMI of over 30 had lower HRV (many measurements) than lower BMI subjects, and waist circumference was better correlated with lower HRV than body mass index (BMI). Syme et. al., 2008 had an interesting related study as they were investigating the relationship between intra-abdominal fat (IAF) (simplified: another name for visceral fat) and metabolic syndrome (MS) in 12 to 18 year old. MS was completely absent in subjects with low IAF, but 8.3% of females and 13.8% of males with high IAF had MS. Additionally, high IAF subjects had altered autonomic nervous system response with higher sympathetic responses, associated with lower HRV. Erectile dysfunction was recently found to be related to higher sympathetic activity (Dogru et. al., 2008). I guess if I wanted to increase my googleness and reading rate I should have written a seperate blog piece on this subject with appropriately intriguing title.
Okay, those are only a few examples of recent papers finding more health conditions associated with higher sympathetic activity and lower HRV. But then the question becomes what can you do to increase your HRV. Probably the most well studied is appropriate exercise can increase HRV (I will go into more detail later), but for now see my previous piece. There is also a very recent paper that is freely available that examined exercise and HRV published in Plos ONE (Earnest et. al., 2008). But what about other options to increase HRV?
Researchers have found that a vegan diet increased HRV, which was related to LDL cholesterol levels (Fu et. al., 2008). Now a vegan diet might be considered too extreme by the average population, what about other dietary manipulations (another extreme diet: every other day fasting (EODF) has been shown to increase HRV, Mager et al., 2006) ? Fish consumption is linked with increases in several measurements of HRV and in a study of over 1,000 subjects that had a follow-up period of 10.8 years found that some of these HRV indicies related with fish consumption (short term fractal scaling exponent) had up to 8.9% differences in relative risk of cardiac death (Mozaffarian et. al., 2008). As most of you know there has been several studies showing wide health benefits of fish consumption (but apparently don’t fry your fish) including for heart health.
Can your general disposition affect HRV? During high stress conditions, be it giving a speech,or exercising, there is a decrease in HRV, but interestingly people with higher self-esteem display less of a HRV decrease during a speech task (O’Donnell et al., 2008). Now at first glance this makes perfect sense, the people with higher self-esteem feel less stress under this task because of their confidence. At a second level it suggest that more self-confident people (high self-esteem) would undergo less stress in their overall life and have higher HRV (over their lifetime) and is this predictive of a longer lifespan? Now you might argue that you do not have much direct control over your self-esteem, but I guess at least try, and try hard not to have low self-esteem (easier said than done).
So the point of this piece was to update you with some of the latest research in HRV. Obesity, and more specifically waist circumference, visceral fat, is associated with lower HRV. Additionally, erectile dysfunction (ED) is also related with high sympathetic drive (lower HRV). Obviously, the increase of abdominal fat (visceral) could be related to the ED. Either way I don’t think anybody particularly wants to either to be fat or have ED.
Now I think people should be forward thinking, sure they might not be too overweight, or have ED currently. But could HRV give us a concrete measurement prior to these more severe health conditions (diabetes, ED, depression, CVD, …. death) that we can monitor on a daily, weekly, monthly basis. Of course one must take the next step and do the best they can to either maintain your current level of HRV (HRV decreases with age) or increase HRV with various lifestyle changes (better diet - fish, fasting, vegan, etc and exercise).
Tomorrow, I will give you more detail on how the average person can actually monitor their HRV without reliance on the health care system (they probably wouldn’t give you monthly readings or it would come at a relatively high cost).