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Resting heart rate (RHR) is a fundamental clinical parameter that reflects the number of heart beats per minute when at rest. It is an easy-to- measure bed side clinical variable that can be used to gauge your cardiovascular and metabolic health. In fact, RHR is a sensitive indicator of the interplay between the sympathetic (fight or flight) and parasympathetic (relaxed) system. Sympathetic overactivity contributes to a high RHR and an increased risk of chronic diseases. Conversely, lower RHR reflects an efficient heart muscle function and is a positive prognostic indicator of cardiovascular fitness.
To measure your RHR, a heart rate sensor can be used. Alternatively, you can measure it by feeling your radial pulse (at the wrist beneath the thumb) and counting the number of beats in 20 seconds and then multiplying that by three. The American Heart Association recommends measuring your RHR first thing in the morning whilst in bed to eliminate the influence of external factors.
RHR is normally between 60-100 beats per minute (bpm). However, an athlete can have a normal RHR at 30-40 bpm. Several factors can influence it and therefore cause day to day or person to person variation. For instance, genetic factors such as gender can play a role – women tend to have slightly higher RHR. Other external and internal factors include: physical fitness and level of activity, diet (alcohol, caffeine, and salt consumption), smoking, body mass index (BMI), emotions, pre-existing heart disease, and drugs. All of which instigate imbalances between the sympathetic and parasympathetic causing variations in the RHR.
Lower RHR is directly related with a higher life expectancy. In the last decade, several studies revealed a significant relationship between elevated RHR ,chronic diseases, and total mortality. For instance, a prospective based cohort study of more than 40,000 men and women with a mean age of 55 years, published in 2018, demonstrated that an increase in the RHR of 10 bpm from baseline was associated with an 11%, 8%, and 20% increase in heart diseases, cancer, and other all-cause mortality respectively – with gender and lifestyle factors adjusted for.
An elevated RHR occurs due to the overstimulation of the sympathetic system which in turn increases the oxygen demands of the heart muscle due to the increased workload. Blood supply to the heart is primarily delivered during the relaxation phase of a heartbeat. This phase shortens as the RHR increases causing an imbalance between oxygen demand and supply placing extra strain on the heart muscle. Moreover, sympathetic activity stimulates the renin-angiotensin-aldosterone system (RAAS) resulting in increased production of angiotensin 2. The latter acts on blood vessels promoting atherosclerosis (plaque formation that stiffens and narrows arteries) and on the heart muscle mediating its fibrosis. It also promotes salt and water retention, via the kidneys, increasing the blood pressure. The combined effect of narrowed blood vessels, impaired blood and oxygen supply, and fibrosis increase the risk of heart attacks, fatal irregular heart rhythms, sudden death, and high blood pressure.
Furthermore, a possible link between elevated RHR, high blood pressure, and obesity is leptin production, a hormone produced by fats cells. It upregulates sympathetic activity in the kidney activating RAAS which increases blood pressure. Therefore, an elevated BMI is a red flag for elevated RHR and heart disease.
A systematic review and meta-analysis published in 2021 evaluated the relationship between RHR and cancer. In conclusion, their analysis revealed : 1) a positive association between elevated RHR and the risk of cancer and 2) that a RHR less than 60bpm seems to be protective. The exact mechanism of this association is complex and not fully understood, however several theories exist. One plausible theory attributes the risk of cancer to the over production of growth and pro-inflammatory factors, due to the hyper-stimulated sympathetic system. These factors stimulate the uncontrollable division of abnormal cells and new blood vessel formation in amidst a state of hyperinflammation. These combined form a breeding ground for cancerous growths. It is prudent to note that genetic factors and environmental factors such as BMI, smoking, and physical inactivity are also important risk factors for cancer development that have to be taken into consideration.
A chronically upregulated sympathetic response can result in a state of insulin resistance. This impairs the body’s ability to reduce blood sugar levels increasing the risk of type 2 diabetes as portrayed by a prospective cohort study and meta-analysis (2018). The state of insulin resistance is linked with high levels of uric acid and triglycerides and low levels of high density lipoproteins (good cholesterol) – all of which have a direct damaging effect on the endothelium (inner lining) of blood vessels promoting atherosclerosis and high blood pressure. It is important to note that this relationship is also heavily influenced by other variables such as BMI, age, and lifestyle.
Regular physical activity and exercise have been proven to reduce the RHR. A systematic review and meta-analysis (2018) conducted on 16 trials revealed that both yoga and endurance training, such as running, swimming, and cycling, contribute to a an approximately 8.4% reduction in RHR in individuals after three months of three training sessions per week. Diaphragmatic deep breathing in yoga training activates the stretch receptors in the lungs which stimulate parasympathetic activity promoting a relaxed stress free state. The synergistic effect of stress reduction and parasympathetic activity contribute to the reduction in RHR. Conversely, strength training exercises had no impact on the RHR.
Another proven method of reducing RHR is through dietary intervention. Several studies have demonstrated the beneficial effect of Mediterranean diet on reducing the incidence of heart disease. This was further validated by the findings of the NUTRIVASC study that investigated the cardioprotective effects in participants, with no previous history or risk factors of heart disease, that adhered to the French Nutrition and Health Program guideline – higher vegetable intake and lower caloric , saturated fat and added sugar intake. Essentially, participants who adhered to the diet had a lower RHR. Interestingly, consumption of omega-3 fatty acids can also significantly reduce the RHR.
Furthermore, smoking is a main culprit for an elevated RHR and heart disease. A recent exploratory study (2020) was conducted to monitor RHR to verify abstinence from smoking. Results of heart rate measurements showed a reduction on days of abstinence when compared to smoking days. Therefore, it is prudent to discuss smoking cessation and possible nicotine replacement therapy with your General Practitioner to help move your RHR in a favourable direction decreasing your risk of heart disease.
Additionally, a cohort study (2014) demonstrated the significant risk of heavy binge drinking (≥12 drinks on one occasion) and high RHR on heart disease when compared with non-drinkers. This association was noted even after controlling other lifestyle variables. A possible explanation is the increased risk of development and progression of atherosclerosis. Therefore, it is important to monitor the RHR in heavy drinkers and to encourage them through counselling services and detoxification programmes to reduce their daily alcohol consumption to help tackle this risk.
A RHR between 50-70 bpm is associated with a lower mortality rate. However, achieving the same targets with medications, such a β-blocker, is associated with double the mortality. Therefore, it is vital to reduce the RHR through lifestyle modification to achieve the desirable health benefits.
Resting heart rate: what is normal?
https://heart-bmj-com.libgate.library.nuigalway.ie/content/104/13/1048
Resting heart rate and the risk of cardiovascular disease, total cancer, and all-cause mortality – A systematic review and dose–response meta-analysis of prospective studies (2017)
https://www-sciencedirectcom.libgate.library.nuigalway.ie/science/article/pii/S0939475317300856?via%3Dihub
Resting Heart Rate as a Predictor of Cancer Mortality: A Systematic Review and Meta-Analysis (2021)
https://www-mdpi-com.libgate.library.nuigalway.ie/2077-0383/10/7/1354
Dose-response association of resting heart rate and hypertension in adults
https://journals-lww-com.libgate.library.nuigalway.ie/md-journal/Fulltext/2020/03060/Dose_response_association_of_resting_heart_rate.42.aspx
Resting heart rate and risk of type 2 diabetes: A prospective cohort study and meta-analysis (2018)
https://onlinelibrary-wiley-com.libgate.library.nuigalway.ie/doi/full/10.1002/dmrr.3095
Uric acid and hypertension
https://www.nature.com/articles/s41440-020-0481-6
Effects of Exercise on the Resting Heart Rate: A Systematic Review and Meta-Analysis of Interventional Studies
https://www-mdpi-com.libgate.library.nuigalway.ie/2077-0383/7/12/503
Yoga, mindfulness-based stress reduction and stress-related physiological measures: A meta-analysis https://www.sciencedirect.com/science/article/abs/pii/S0306453017300409?via%3Dihub
Association Between Adherence To The French Dietary Guidelines And Lower Resting Heart Rate, Longer Diastole Duration, And Lower Myocardial Oxygen Consumption. The NUTRIVASC Study
https://www.dovepress.com/association-between-adherence-to-the-french-dietary-guidelines-and-low-peer-reviewed-fulltext-article-VHRM
Reduction of heart rate by omega-3 fatty acids and the potential underlying mechanisms
https://www.frontiersin.org/articles/10.3389/fphys.2012.00416/full
Decrease in Resting Heart Rate Measured Using Smartphone Apps to Verify Abstinence From Smoking: An Exploratory Study
https://www-ncbi-nlm-nih-gov.libgate.library.nuigalway.ie/pmc/articles/PMC7364830/
Modifying Effects of Resting Heart Rate on the Association of Binge Drinking With All-cause and Cardiovascular Mortality in Older Korean Men: the Kangwha Cohort Study
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4074631/
