Heart rate variability (HRV) is an important metric that gives a fascinating insight into the subconscious response to stress of your nervous system.
What is it?
HRV is the shift or variability of time between consecutive heart beats.
If you have a rest heart beat of say 50, it is extremely unlikely you will have those beats separated by exactly one second each. In reality the time between beats will be fractionally different. This variance exists whether your heart rate is high or low.
The HIGHER the variance or average time between heart beats, the better.
In short:
High HRV = Good
Low HRV = Bad or less good
The variance between the beats is perfectly normal and is not anything associated with arrhythmia.
So why is it an important measurement of stress and how do changes occur?
The link between your brain and your heart via the autonomic nervous system dictates how fast your heart beats. When you are more stressed (physically, emotionally, through lack of sleep or other changes that could be causing stress), this increases the tone or activation of the sympathetic branch of the nervous system.
The sympathetic branch is your fight and flight system. A couple of the things that increased sympathetic activation affects are the increases in heart rate and blood pressure. Increases to heart rate and blood pressure are normal when the time calls for it, not for when you are sat on the sofa or lying in bed.
Increased sympathetic nervous system tone will result in a DECREASE in HRV.
A lowering in sympathetic tone and an increase in parasympathetic tone will result in an INCREASE in HRV variability.
Decreased HRV is a sign that you adaptation to stress is low; which also effects your body’s ability to adapt to future stress.
A high number represents an increase in the average time between beats of your heart. A high HRV is a great indicator that you are good to go and are likely to be able to take on a decent amount of physical or emotional strain.
Chronically, very low HRV has been linked to increased rates of diabetes, cardiovascular disease, inflammation and other chronic conditions.
WHAT SPECIFICALLY EFFECTS HRV?
The biggest factors that affect acute or chronic changes to HRV are:
1. Emotional stress
Moderate to high states of emotional stress are almost guaranteed to have a negative effect on HRV. Chronic stress from depression, anxiety, work, family or health are all key emotional factors that affect our wellbeing. Your HRV will also change and likely lower during these periods.
2. Sleep
I say this all the time; sleep is the bedrock upon which all health is built upon. Sleep is an active process and takes place over the course of the night and requires a lot of contributing factors to complete the tasks of recovery. Having reduced hours of sleep is the first way which will negatively impact HRV as much as increased hours of sleep will likely have a positive impact. The quality of your sleep and by quality we mean the time spent in restorative vs light sleep is another huge factor in the recovery process of the body.
The health of your circadian will also affect this. Take a look at my blog on sunlight and circadian for more info on this.
3. Physical stress or strain
If you have a very physical job or are training in the gym or doing sport on top of an already busy lifestyle, your HRV is likely to lower in response to this increased demand on the sympathetic arm of your nervous system.
For anyone interested in peak physical performance or improvements in their sport will know, its a balancing act between training hard and resting enough to avoid burnout or going over the top.
4. Nutrition (both what and when you eat)
The quality of the food you eat is an obvious benefit to all areas of health, including improving HRV. A diet that has limited nutritional value containing few vitamins and minerals, relying instead on processed sources of proteins, fats and sugars will result in all areas of health being affected. Omega 3 fatty acids, vitamins c, d and magnesium have in studies all shown to be cardioprotective and have benefits to HRV.
Consuming enough calories dependant on your own personal needs or activity levels can effect short term changes to HRV. If you have a day of a lot of physical or emotional strain, your calorie requirements to aid with recovery from this will be higher. If you fail to meet those needs, your sympathetic nervous system is likely to be the dominant factor going into sleep and will thus effect HRV. This approach is more nuanced and reflects the smaller picture of your day to day caloric needs but one to be mindful of.
However, over the longer term, numerous studies have found that some form of caloric restriction, be it dieting or fasting has overall improvements on HRV. Especially as we age. The conclusions of these studies theorise that maintaining a healthy fat/muscle mass ratio and healthy metabolism are the key drivers behind these observations.
How late you finish eating is also a huge factor on recovery and HRV. Eating closer than 2-3 hours before bed has been found to reduce HRV. Digestion is a parasympathetic activity and thus competes for parasympathetic tone over other recovery processes that occur during sleep.
5. Alcohol
Sadly, for those that enjoy an alcoholic drink, the right amount of alcohol is no alcohol if you are concerned with your HRV. It is universally one of the worst things you can consume (especially of an evening) that will negatively effect your HRV. One way to mitigate some of the negative effects of alcohol is to drink earlier in the day and to stop drinking as early as possible. This gives your system a decent chance to metabolise as much of the alcohol in the blood, prior to going to bed.
6. Hydration
This is a simple one. You don’t drink enough, you will put extra stress on all systems in your body.
7. Age
Sadly, like all things in life, things degrade gradually over time. HRV is one of them that gradually decreases over time. Although HRV is unique to each individual and some people will naturally have slightly lower HRV than peers of the same age and remain perfectly healthy, these numbers will still decrease slightly as the decades pass. That doesn’t mean you can’t exceed the normal values for your age group and many people manage it.
8. Diseases and infection
Almost all states of ill health will decrease HRV. For those that measure regularly, an unusual drop in HRV could predict the onset of a cold or illness. Sustained drops in HRV could also, be a sign of something more sinister (if no other stressors or variables have changed) and can be a good indicator to get yourself checked out.
9. Increases in external and internal temperature
Heat increases sympathetic nervous system activity and thus will have a lowering effect on HRV.
10. Pain
Pain is a big driver of increased sympathetic tone and those in chronic pain could expect their baseline HRV values to be lower than what they could be. Reducing the factors that are contributing to pain and desensitising the down stream increases to sympathetic tone is a key part of the treatment process here. A more parasympathetic environment is one in which promotes healing which is why balancing that side of the system is a major goal for all patients.
11. The time of the year (in particular if you live in the Northern Hemisphere)
Studies have shown that average HRV values fall during the winder. This is most likely linked to a drop in vitamin D levels because of reduced sun exposure. Another reminder if you need one, to get as much sunlight as possible and to supplement with vitamin D rich foods (oily fish, red meat, liver, eggs, butter, whole milk) and a vitamin D3 and vitamin K2 supplement.
WHAT CAN YOU DO TO IMPROVE HRV VALUES?
1. Improve sleep quality and performance
Consistency plays a big part in sleep performance. Trying to get to bed and awaking at similar times each day is crucial for circadian consistency and trying to get at least 7 hours total sleep time if possible. This is the benchmark number that north of 90% of the worlds population need to meet recovery requirements.
2. Get in as much sunlight as possible
No matter the time of year try to get outside as much as you can to ensure that vitamin D levels are stocked up. Supplement with Vitamin D + Vitamin K2 if you are in a particularly low sunlight area or if your routine does not allow for much time outside.
3. Increase cardiovascular fitness
The benefits to increasing your cardiovascular fitness extend way beyond HRV but it is also one of the biggest bang for your buck changes you can make which could push your HRV into the upper ranges for your age range, no matter your age.
4. Avoid alcohol or stop drinking as early in the day as possible
5. Practice methods like yoga, yoga Nidra, mediation or breath work to increase the parasympathetic arm of the nervous system
Engaging in activities or practices that increase parasympathetic nervous system activity is a way to help calm the nervous system and counter act against some of the stressors in your daily life.
6. Supplement
There are some supplements that you can add to a balanced diet and lifestyle that may also help increase HRV by aiding sleep or aiding with lowering of the stress hormone cortisol. Supplements like Ashwaghanda help to lower cortisol which is a major driver of the sympathetic response to stress.
Other supplements that aid with reducing inflammation and promoting homeostasis in the individual are all likely to yield positive results with HRV increases. What you as an individual may need is likely to be specific to you. But you could explore (as mentioned) Vitamin D+K2, Vitamin C, Omega-3 fatty acids, L-theanine, NAC.
So many factors may be contributing and before taking supplements I always recommend you ensure that the fundamentals of sleep, diet and exercise are solid and taken care of. When you have a solid foundation of health practices you can start to narrow down the variables that may move the needle so to speak with regards to HRV.
7. Stay hydrated
Optimal hydration is a key part of health. Making sure you drink enough water and maintain a balance of electrolytes from your food or other sources if needed can make a significant difference in recovery and HRV.
8. Keep your bedroom cool
Heat was mentioned above as an environmental factor that negatively affects HRV. Mitigating against increases in heat is most important at night as in order to get into deeper, restorative sleep, your body needs to cool its core temperature.
No matter the time of year, having a cool bedroom will help reduce that core temperature, leading to more efficient sleep and increased parasympathetic tone.
WHY MIGHT YOU WANT TO TRACK YOUR HRV?
As you can tell from the information above, HRV is a key metric to measure with regards to your subconscious stress response. There are a lot of factors that can positively or negatively affect HRV and sometimes it is difficult to tell which changes or adjustments to your lifestyle may be impacting it. By recording your HRV, you can see the acute day to day fluctuations that a new job, nutritional change or bed routine might be having on it. Over time you can get a clearer picture of how your subconscious is responding to stress or mitigations you are adding to help balance things.
If you are an athlete, tracking your HRV should be something you consider, as changes to HRV can occur during a training cycle and will be an indicator to your body’s response to the current intensity/volume/recovery methods you are working with. This is information you can use to adjust things as you go to ensure that you are making the most of your training and also to prevent burnout.
However you choose to track or record HRV, just having access to this one simple number can help shape your decisions about your own health. You change your diet, you can adjust your movement or exercise, you can improve your sleep habits, get outside in the day, drink a little more or supplement a little. The number of variables that you have the potential to adjust are huge and should give you hope that you can make many small decisions or changes that will drastically improve your quality of life.
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