Follow Your Heart: Heart rate variability (HRV) explained

While HRV tends to decline as we age, studies have looked at the connection between low HRV and the risk for cardiac diseases. HRV measures differ significantly across age groups, with older adults typically showing lower HRV compared to younger individuals. Low HRV scores indicate sympathetic overactivity, which is correlated with age-related diseases and conditions, including cardiovascular disease, hypertension, and heart failure [4]. HRV often decreases with age and is associated with an increased risk of disease. In research, specific measures and HRV measures such as SDNN, LF, and HF are used to assess autonomic function and predict health outcomes.

Another study found that HRV-related parasympathetic function decreases with age, reaching its lowest point in our 80s; however, after our 80s, something interesting happens: there is a reversal and increase in our parasympathetic function, which is more characteristic of younger populations [5]. This pattern is observed when analyzing heart rhythm and its variability in different age groups. Core body temperature and circadian rhythms also play a role in regulating HRV and are linked to healthy aging and longevity.

Consistently high HRV rates in the elderly were also a predictor of longevity [5], and centenarians with a higher HRV also had greater survival rates (about 1.6 additional years) [6]. Compared to the general population, centenarians often display unique HRV profiles and better health outcomes. In addition, cardiovascular health is closely related to rate and blood pressure, as well as heart rate and blood metrics, all of which are influenced by HRV. HRV analysis is frequently performed in a medical setting to assess longevity and disease risk.

HRV is shaped by several factors, including both the non-modifiable genetic factors we inherit and the modifiable factors within our control. Key factors that affect HRV include physical activity, enough sleep, mental health, cholesterol levels, and the presence of heart conditions. Lifestyle habits, such as regular exercise, managing stress, and avoiding excessive alcohol, also significantly affect HRV.

HRV reflects the body's ability to adapt and how well the body handles stress in daily life. Higher HRV is associated with being well rested and can help the body recover faster from both physical and mental strain. Mental health and mental health issues, such as anxiety and depression, can influence HRV, making it a useful indicator for both physical and mental well-being.

HRV is an important marker of overall health, complementing traditional cardiovascular metrics like cholesterol levels. Health data from wearables and trackers can be used to monitor HRV, though tracking HRV has both benefits and limitations for stress management. Research uses specific measures, such as SDNN, LF, and HF, to assess HRV and its relationship to health outcomes.

Physical activity is crucial for maintaining and improving HRV, while getting enough sleep is essential for optimal HRV levels. HRV can also signal potential heart conditions, highlighting the importance of accurate measurement methods. Regularly tracking HRV provides insights into how the body responds to stressors in daily life and helps guide healthy lifestyle choices.

Studies have found that genetics may determine up to 60% of individual differences in HRV [7]. Family and twin studies have also found a significant genetic contribution to HRV, with heritability estimates reaching as high as 71% [8].

Men tend to have a slightly higher HRV than women [9]. It’s also normal for HRV to fluctuate in women throughout their menstrual cycle, with HRV being higher during the low-hormone follicular phase (the first half of the cycle) and dropping during the high-hormone luteal phase (the phase right before menstruation). This tells us that women may be more primed to take on stress (AKA intense workouts) during the first half of their cycle while benefiting from more restorative, low-intensity activities during their lower-HRV luteal phase [10, 11]. Pregnancy also causes a temporary drop in HRV [12]. 

Drinking alcohol has not only been shown to increase heart rate but also significantly lower HRV. Data analysis conducted by Whoop (a wearable tracker business) found that athletes who drank had a 16.2% higher heart rate (HR) and a 22.7% lower HRV the next day, as compared to non-drinkers. These same athletes also showed reduced recovery metrics (aka HR and HRV) for 4-5 days post-alcohol consumption [13]. 

Sleep is crucial for recovery. It also shifts the body into a more parasympathetic tone [14]. So, it’s not surprising that both sleep deprivation and poor sleep result in a lower HRV [15, 16]. Another study found that poor sleep quality and increased daytime dysfunction were related to lower HRV [17]. 

While regular exercise is one of the best ways to increase HRV [18], exercise intensity is what influences HRV [19]. It’s normal for high-intensity exercise and endurance training to result in an acute decrease in HRV and slower HRV recovery [20]. After sufficient recovery, a high HRV is also a strong predictor of training adaptation. A downward-trending HRV may occur during overload training (increasing weights over time to build adaptation), but after recovery, HRV should return to baseline [21]. 

These are only some of the factors that can impact HRV. Everything from age and health conditions to circadian changes (e.g., jetlag), perceived stress, and air pollution can also affect your HRV. 

Want to boost your HRV and achieve a more balanced nervous system? Here are some simple everyday habits that may help: These habits can help reduce stress and lead to less stress overall, supporting your well-being. Achieving a relaxed state is associated with higher HRV, better recovery, and increased feelings of calmness. Improving HRV is linked to changes in the heart's electrical activity, which can be measured using devices like ECGs. Physiologically, these habits help balance the sympathetic and parasympathetic nervous systems, counteracting the fight or flight response and promoting rest and recovery.

Prioritizing hydration is key to HRV, as dehydration triggers the parasympathetic nervous system, lowering HRV. One study found that even mild dehydration reduced HRV in men and women [22]. Older adults and women during the luteal phase of their menstrual cycle are more susceptible to dehydration. 

Any type of regular exercise, aerobic or anaerobic, can increase HRV. Exercising out in nature, such as a walk or hike, has also been shown to boost HRV [23]. High-intensity exercise was shown to improve HRV the most in physically inactive adults, compared to moderate-intensity training [24]. However, too much strenuous activity can prevent the body from adequately recovering. Tracking your HRV consistently can help you adapt your training to better fit your body’s needs. 

While both aerobic exercise and strength training can increase HRV, it’s important to recognize the positive impact rest and recovery have on a higher HRV. Overtraining leaves us stuck in “fight or flight” mode, which decreases HRV over time [25]. If you workout regularly and notice a steady increase in resting heart rate along with a downward trending HRV over days, a rest day may be in order. 

Nine out of 10 Americans don’t get enough fruits or vegetables [26], but if you want to help boost your HRV, this is another reason to add more leafy greens—namely, spinach, mustard greens, and lettuce— to your diet [27]. 

Individuals who participated in a 6 breaths/minute breathing exercise for 10 minutes a day had a higher HRV than the groups that performed rhythm breathing or watched a nature video [28]. Another study conducted on young men found a significant increase in HRV in just four weeks of daily 20-minute sessions of resonance breathing (taking 4.5-7 breaths per minute) [29]. 

One study found that individuals who participated in gratitude journaling showed increased HRV both during their journaling practice and post-journaling compared to individuals who did not journal [30].