Low HRV: Causes and What You Can Actually Improve

The practical conclusion from this review is that there is no single universal 'good' HRV value. A healthy 25-year-old may have an RMSSD several times higher than a healthy 55-year-old, and two people of the same age and similar fitness can differ twofold. So the question 'is my 35 ms low' makes no sense without knowing the measurement method, age, time of measurement and your own history of results.

The value is influenced above all by age (HRV declines with age), genes (a considerable part of the variability is inherited), sex, aerobic fitness, body weight, body position and breathing during the measurement. Hence the basic rule: compare yourself only with yourself, with the same device, under the same conditions. For people who want to learn to read the changes, the key is to establish a baseline from at least 2–4 weeks of measurements and then watch deviations from it, not the absolute value.

HRV is by nature variable from day to day. Even in a healthy, regularly living person, one night can differ from the next by 10–20% or more with no clear reason. A one-off drop can be influenced by a late meal, alcohol, a hot bedroom, an argument before bed, a hard workout the previous day, an infection starting up, or simply a worse night. A sensible interpretation is therefore based on a 7-day rolling average compared with a baseline from several weeks, not on a single value.

The second important thing is the direction of change. A drop in average HRV lasting 5–7 days together with a rise in resting heart rate is the typical pattern of accumulated fatigue, short sleep or an oncoming illness. Conversely, a gradual rise in HRV over months with a stable or falling resting heart rate usually reflects improved fitness and recovery. It is therefore worth viewing HRV alongside resting heart rate, which we discuss in a separate article on the normal resting heart rate, and alongside how you feel and how well you sleep.

Do not treat HRV as a moral verdict on your day either. It is one of several sensors of autonomic state, subject to measurement error, imprecisely processed by the manufacturer's algorithm and sensitive to things you cannot control (menstrual cycle phase, ambient temperature, altitude). When you feel great and the watch says 'low HRV', trust your own sense of well-being and review the trend rather than changing your plan on the basis of one number.

Sleep is the most important but most often overlooked factor. Short sleep lowers RMSSD, exactly the measure most devices include in the nightly result. A paradoxical mechanism adds to it: the lower the HRV, the worse the sleep and the worse the recovery, creating a vicious circle. Sleep apnea, snoring and night awakenings further stimulate the sympathetic system. We write about alcohol, which lowers nighttime HRV even when you feel rested, in a separate article on alcohol and HRV despite sleep.

The second group of causes is illness and inflammation. Viral and bacterial infections, fever, inflammation after a vaccination, painful periods, a flare of a chronic disease or an ordinary cold often lower HRV 1–2 days before symptoms appear and keep it low for several days after they subside. Add to this dehydration, heat, altitude, pregnancy, iron deficiency, an overactive or underactive thyroid and some drugs (for example beta-blockers change heart rate and indices, and antidepressants and antihistamines with anticholinergic action can lower HRV).

The third group is stress and training load. Chronic psychological stress, tension at work, lack of rest, intense training without enough recovery, as well as caffeine late in the afternoon or a heavy dinner right before sleep push the balance toward the sympathetic system. As we describe in the articles on evening training and heavy leg training, the effect of one big session on HRV the next night can be clear but temporary.

Caution is needed here. Population data concern clinical measurements (usually several-minute or 24-hour ECG recordings), not a nightly value from a ring or watch, and describe the risk of groups, not of one person. Moreover, these are observational associations: low HRV accompanies obesity, hypertension, diabetes, low fitness and inflammation, so part of the effect comes from those factors. There is no evidence that artificially raising the watch value in itself reduces the risk of heart attack or stroke.

The best-documented intervention is regular endurance training. Sandercock's meta-analysis shows a moderate, significant rise in HRV measures after a period of training, though smaller in older people. In practice this means several hours a week of aerobic activity at moderate intensity, with one or two units of higher intensity, including zone 2 work, described in the entry in the knowledge base. The effect develops over weeks and months, not days, and disappears when training stops. It is also important not to overdo it: too many intense sessions without rest lower HRV.

The second group is reducing excess body weight. A systematic review of 27 studies on weight change (including 7 controlled trials) indicates that weight loss through diet and exercise is usually associated with a rise in RMSSD and HF and a fall in LF/HF, that is, with greater parasympathetic activity, while weight gain shows the opposite pattern. The authors stress, however, that the quality of evidence was low or very low and the results were not consistent. The third group is sleep: regular times, sufficient length and treatment of sleep apnea if present, because these are the factors that most often explain low HRV in people who otherwise have a good lifestyle.

The fourth group is breathing and stress reduction. A meta-analysis of 24 studies (484 participants) showed a large reduction in subjective stress and anxiety after HRV biofeedback training, but that is an effect on well-being, not proof of a lasting rise in resting HRV. We describe the protocol details in the article on resonance breathing. The fifth group is limiting alcohol and late, heavy meals, which predictably lower nighttime HRV, and treating secondary causes (hypothyroidism, iron deficiency, sleep apnea).

On the other hand, expensive supplements marketed as 'raising HRV', cold showers as a way to permanently increase the value, or yet more gadgets have no convincing evidence. Magnesium, omega-3 or adaptogens may matter when a deficiency or a specific problem existed beforehand, but in people without a deficiency the effect on HRV, if any, is small and inconsistent. First get sleep, movement, alcohol and stress in order.

The same goes for the concept of 'overtraining'. A drop in HRV does not by itself mean overtraining, because the same pattern is produced by poor sleep, stress or infection. In athletes, however, a prolonged drop in HRV combined with poorer well-being, a fall in performance and a raised resting heart rate is a reasonable basis for reducing the load.

In case of worrying symptoms the first step is usually a resting ECG and basic blood tests (blood count, TSH, ferritin, glucose), and if rhythm disturbances that occur in episodes are suspected, Holter monitoring. We describe them in the entries on the resting ECG and Holter ECG. We also write about palpitations and their diagnosis in a separate article.

Treat HRV like a weather indicator, not a verdict. Build a baseline, look at the weekly average and react to lasting deviations: first check sleep, alcohol, infection and training load, and only then look for deeper causes. The biggest lasting rise in HRV comes from boring, well-studied things: aerobic exercise, regular sleep, a sensible body weight and moderation with alcohol. If the watch starts to fuel anxiety about your own body, put it aside for a few days: that, too, is a reasonable intervention.