Resting heart rate as a potential biomarker

Everyone has a heart rate, so everyone needs to pay attention. But what does that heart rate, or pulse, tell us beyond the obvious fact that we are alive?

Our “normal” resting heart rate is between 60 to 100 beats per minute. We know that a RHR above 100 bpm is abnormal; it is referred to as tachycardia, or a racing heartbeat, and has potentially serious consequences. However, even “normal” RHRs can be stratified to identify risks for diseases. What I mean is that, even in the “normal” range, as your resting heart rate increases, so do your potential risks. Actually, RHR below approximately 70 bpm may be ideal.

The importance of the resting heart rate should not be underestimated. In fact, it may play a role in longevity, heart disease — including heart failure, arrhythmias, heart attacks and sudden cardiac death, and even chronic kidney disease.

The good news is that the RHR is modifiable. Methods that may reduce your rate include medications for high blood pressure, such as beta blockers and lifestyle modifications, including meditation, dietary changes and exercise.

Impact on lifespan

We all want to live longer and healthier lives. Reducing the RHR may be an important component in achieving this goal.

In the Copenhagen Male Study, a prospective (forward-looking) study that followed 2,798 participants for 16 years, results showed that those with higher resting heart rates had greater risk of death (Heart Journal 2013 Jun;99(12):882-7). There was a linear relationship between risk of death and increasing RHR. Those who had a resting heart rate above 90 bpm were at a threefold greater risk of death, compared to those who had a RHR at or below 50 bpm. RHR was inversely related to the amount of physical activity.

Thus, the authors concluded that a “healthy” person with higher RHR may still have a shorter lifespan, with all other factors being equal, such as physical activity and blood pressure.

In contrast with the previous study, the following one took a “glass is half-full approach” to longevity. The Jerusalem longitudinal cohort study showed that elderly women and men who had a lower RHR lived the longest (J Am Geriatr Soc. 2013;61(1):40-45). There were more than 2,000 participants, ranging from 70 to 90 years old.

Heart disease mortality

In the Nord-Trondelag health study, a prospective observational study, those with a higher RHR at the end of the study than they did 10 years prior, at the beginning of the study, were more likely to die from heart disease (JAMA 2011; 306:2579-2587). In other words as the RHR increased from less than 70 bpm to over 85 bpm, there was a 90 percent greater risk of heart disease, compared to those who maintained a RHR of less than 70 throughout the two measurements. This study involved 30,000 participants, but unlike some other studies, many of us can relate to the population: They were at least 20 years old and were healthy volunteers.

Heart attacks

It is more common for women to have heart attacks with atypical symptoms than men. Therefore, it is very important for women to reduce their risks. In the Women’s Health Initiative, results showed a 26 percent decrease in the risk of cardiovascular events in those postmenopausal who had a RHR below 62 bpm, compared to those who had a RHR above 76 bpm (BMJ. 2009 Feb 3;338:b219). Interestingly, these results were even more substantial in the subgroup of women who were newly postmenopausal, ranging in age from 50 to 64.

Effect on kidney function

Since I wrote about chronic kidney disease on May 9, I thought an interesting follow-up might be resting heart rate and its impact on kidney function. In the Atherosclerosis Risk in Communities Study, results showed that the most severe form of chronic kidney disease, end-stage renal disease, was 98 percent more likely to occur in those with the highest RHR, compared to those with the lowest (J Am Soc Nephrol. 2010 Sep;21(9):1560-70). There were approximately 13,000 participants in the study, with a 16-year follow-up.

The authors hypothesized that this negative affect on the kidney may be due to a loss of homeostasis in the autonomic (involuntary) nervous system, resulting blood vessel dysfunction, such as increased inflammation and vasoconstriction (narrowing).

Eating fish

What can be done to reduce the resting heart rate with minimal side effects? Fish consumption has recently been shown to have a positive effect. In a study, European men who ate greater amounts of fish — more than one serving per week — had lower resting heart rates than those who ate fish rarely (Circulation. 2003;108:820-825). There was also a direct relationship between the amount of fish consumed and the RHR: The more fish consumed per week, the greater the reduction in RHR. This was a prospective observational study involving about 5,000 men. Some beneficial side effects of eating fish included decreased triglycerides and diastolic (lower number) blood pressure, as well as increased HDL (“good cholesterol”). Even after controlling for these beneficial side effects, there still was a significant improvement in RHR with fish consumption.

Is there a resting heart rate that is too low? Well, it depends on the context. If you are a marathoner or an athlete, then a RHR in the 40s may not be abnormal. For a healthy, physically active individual, it is not uncommon to have a resting heart rate in the 50s. However, if you are on medications that reduce your RHR and/or have a chronic disease, such as heart failure, it is probably not advisable to go much below 60 bpm. Always ask your doctor about the appropriate resting heart rate for your particular situation.

Thus, resting heart rate is an easy and inexpensive biomarker to potentially determine risk stratification for disease manifestation and to increase longevity, even for those in the “normal” range. We can utilize RHR as tool for primary prevention of disease. The fact that it is modifiable means it is something that we need to monitor, so that we can achieve the ideal RHR, rather than just the “normal.”

Dr. Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, go to the website www.medicalcompassmd.com and/or consult your personal physician.