A reading of 108/73 mmHg falls squarely within the range most medical guidelines consider healthy for adults. It sits comfortably below the 120/80 threshold that marks the upper boundary of “normal” blood pressure, and it is well above the levels where doctors typically start worrying about hypotension. For most people, this reading is a sign that the cardiovascular system is doing its job without undue strain. That said, “normal” on a chart and “normal for you” are not always the same thing, and certain groups of people need to pay closer attention to numbers in this range than others.
Where 108/73 Sits on the Blood Pressure Spectrum
Blood pressure is measured in two numbers. The top number (systolic) reflects pressure in the arteries when the heart contracts; the bottom number (diastolic) reflects pressure between beats. Standard adult guidelines classify anything below 120/80 as normal, 120-129 over less than 80 as elevated, and 130/80 or higher as hypertension. There is no universally agreed-upon threshold for “too low.” Most clinicians consider systolic below 90 or diastolic below 60 as the rough floor where true hypotension begins, and even then, only if the person has symptoms.
At 108/73, both numbers sit in a comfortable middle zone. The systolic is 18 points below the elevated cutoff and 18 points above the rough hypotension floor. The diastolic is 7 points below the normal ceiling and 13 points above the low end. By virtually any clinical standard, this is an unremarkable reading. If you took this measurement and feel fine, there is nothing to investigate.
Why Symptoms Matter More Than the Number
Blood pressure in the low-normal range only becomes a medical issue when it causes symptoms. The body is remarkably good at maintaining adequate blood flow to organs across a wide range of pressures. Feeling dizzy, lightheaded, chronically fatigued, or faint at readings like 108/73 would be unusual for most adults, but not impossible.
A large population study published in the BMJ found a negative association between systolic blood pressure and self-reported tiredness and feeling faint, meaning that as blood pressure dropped, these symptoms became somewhat more common. The association was strongest in women under 50.1British Medical Journal. Symptoms of low blood pressure: a population study Importantly, the researchers were looking at a broad population and found that these symptoms tracked with lower pressures in a gradient fashion. That does not mean everyone with a systolic of 108 feels tired. It means that if you do feel persistently fatigued or woozy, your blood pressure could be contributing, and it is worth mentioning to a doctor.
The practical rule is straightforward. If you have no symptoms, 108/73 is simply a healthy reading. If you are experiencing dizziness when standing, persistent fatigue, blurry vision, or episodes of near-fainting, the reading provides useful context for your doctor even though the number itself is not alarming on paper.
The J-Curve Concern for People With Heart Disease
Here is where the story changes for a specific subset of people. If you have coronary artery disease, significant narrowing of heart arteries, or severe left ventricular thickening, a diastolic reading of 73 could actually be worth watching. Research has identified what is called a J-curve effect: cardiovascular complications can increase not only when blood pressure is too high but also when it dips below certain thresholds, particularly on the diastolic side.
A review of large clinical trials found that this J-curve effect appears at a diastolic pressure of roughly 70-80 mmHg and a systolic below about 130 mmHg in patients with existing cardiovascular disease. The phenomenon is thought to exist because the heart’s own arteries fill with blood during the diastolic phase of each heartbeat. Push diastolic pressure too low in someone whose coronary arteries are already compromised, and the heart muscle may not get the blood supply it needs.2PubMed Central. The significance of the j-curve in hypertension and coronary artery diseases The same review noted that this J-curve does not appear for stroke or kidney disease, because blood flow to the brain and kidneys depends more heavily on systolic pressure.
For a healthy adult without coronary disease, a diastolic of 73 is perfectly fine. For an elderly patient on multiple blood pressure medications who also has clogged heart arteries, that same 73 might prompt a doctor to ease off one of the medications. The guidance from that review was to keep diastolic pressure at a minimum of 70 mmHg and ideally between 80-85 mmHg in high-risk patients with coronary disease or severe heart muscle thickening.2PubMed Central. The significance of the j-curve in hypertension and coronary artery diseases If you have heart disease and are seeing numbers like 108/73 regularly, it is worth discussing with your cardiologist, not because the number is dangerous for most people, but because you are not most people.
Blood Pressure Is a Moving Target Throughout the Day
One reading of 108/73 is a snapshot, not a portrait. Blood pressure fluctuates constantly based on activity, stress, time of day, and even posture. It can swing by 20 or more points over the course of a single day in a perfectly healthy person.
The most predictable pattern is the overnight dip. Blood pressure typically drops during sleep and rises in the early morning hours. A study using 24-hour ambulatory monitoring in young adults found that the average ratio of nighttime to daytime systolic pressure was 0.88, meaning blood pressure during sleep was about 12 percent lower than during waking hours.3PubMed Central. Nighttime blood pressure dipping in young adults and coronary artery calcium 10-15 years later: the coronary artery risk development in young adults study Someone whose daytime blood pressure is 108/73 could reasonably expect numbers closer to 95/65 during deep sleep. That nighttime dip is healthy. People whose blood pressure fails to dip adequately at night actually face higher cardiovascular risk down the road.3PubMed Central. Nighttime blood pressure dipping in young adults and coronary artery calcium 10-15 years later: the coronary artery risk development in young adults study
Hydration status also plays a measurable role. Dehydration reduces blood volume and can impair the body’s ability to maintain pressure when you stand up. Research has shown that even moderate dehydration can worsen orthostatic tolerance, meaning you are more likely to feel dizzy upon standing.4PubMed Central. Hydration Status and Cardiovascular Function If your reading of 108/73 was taken on a day when you hadn’t been drinking enough water, it may be slightly lower than your true baseline. Conversely, after a large glass of water and some salt, you might see a few points higher.
The point is that a single reading is less informative than a trend. If you are tracking your blood pressure at home, try to measure at the same time each day, in the same position, and look at the average over a week or two rather than fixating on any one measurement.
Pregnancy and Naturally Lower Readings
Pregnant women frequently see blood pressure numbers drop into the low-normal range, and 108/73 would be entirely expected during certain stages of pregnancy. The cardiovascular system undergoes dramatic remodeling during pregnancy. One of the earliest changes is dilation of blood vessels throughout the body, which causes systemic vascular resistance to fall and triggers a compensatory increase in cardiac output of roughly 40-50 percent.5PubMed. Physiological changes of pregnancy and monitoring Blood volume increases, heart rate goes up, and despite all that extra blood being pumped, arterial blood pressure tends to decrease, particularly during the first and second trimesters.6PubMed. Physiologic changes during normal pregnancy and delivery
For a pregnant woman, 108/73 is typically a reassuring number. The real concern during pregnancy is blood pressure going too high (preeclampsia), not too low. That said, the lower baseline blood pressure of pregnancy combined with the tendency for blood to pool in the legs can sometimes cause dizziness when standing up quickly. Staying well hydrated and changing positions slowly are simple ways to manage this.
How Thyroid Function Quietly Shapes Blood Pressure
Thyroid hormones are an underappreciated influence on blood pressure, and they are worth knowing about if your readings are consistently on the low side. The thyroid affects how tightly blood vessels constrict, how fast the heart beats, and how much blood the heart pumps with each beat. Changes anywhere along the thyroid spectrum can shift blood pressure.
Hyperthyroidism, where the thyroid is overactive, tends to widen the gap between systolic and diastolic numbers by increasing cardiac output while decreasing vascular resistance. Hypothyroidism does roughly the opposite: it narrows the gap between the two numbers and tends to increase vascular resistance.7PubMed. Thyroid hormone and blood pressure regulation Interestingly, hypothyroidism is more commonly associated with elevated blood pressure than with low readings, because the increased vascular resistance tends to push numbers up. So if you have hypothyroidism and a reading of 108/73, that is likely a good sign rather than a concerning one.
What makes the thyroid connection especially interesting is that even within the “normal” range of thyroid function, variations in thyroid hormone levels correlate with blood pressure differences. A study of nearly 300 subjects found that within the euthyroid (normal thyroid) range, lower levels of circulating thyroid hormone were associated with higher vascular resistance, and the thyroid hormone index independently predicted blood pressure salt sensitivity.8The Journal of Clinical Endocrinology & Metabolism. Thyroid Function and Blood Pressure Homeostasis in Euthyroid Subjects In practical terms, this means that your thyroid status subtly tilts your blood pressure even when your thyroid tests come back “within normal limits.” A person whose thyroid hormones sit at the higher end of normal may have slightly lower vascular resistance and a slightly lower baseline blood pressure than someone at the lower end of normal.
None of this means you should request thyroid testing simply because your blood pressure is 108/73. But if you have other symptoms that could point to thyroid dysfunction, such as unexplained weight changes, persistent cold sensitivity, or changes in energy level, the blood pressure reading adds another data point to the conversation.
Getting an Accurate Home Reading
Before worrying about whether 108/73 is too low, it is worth asking whether the number is accurate. Home blood pressure monitors are convenient, but small errors in technique can easily shift a reading by 5-10 points in either direction. Your 108/73 could actually be 115/78 or 100/68 depending on how the measurement was taken.
The basics are simple but frequently ignored. Sit with your back supported and feet flat on the floor for at least five minutes before measuring. Rest your arm on a flat surface at heart height. Do not talk during the reading. Use the correct cuff size, as a cuff that is too small will overestimate and a cuff that is too large will underestimate your pressure. Newer devices have addressed some of these issues. Advanced home monitors now feature longer inflatable cuff bladders that wrap more completely around the arm, which expands the acceptable range of cuff placement and reduces the chance that slightly off positioning will throw off the reading.9PubMed Central. Home Blood Pressure Monitoring
Arm position alone can swing your results meaningfully. If your arm is dangling at your side instead of resting at heart level, the reading may come in higher than reality. If your arm is raised above your heart, the reading may be artificially low. The difference between a properly positioned arm and a drooping one can be enough to move your systolic from 108 to 115 or higher.
Taking two or three readings a minute apart and averaging them gives a more reliable number than relying on a single measurement. If you are seeing 108/73 consistently across multiple readings taken with good technique, you can trust that it represents your actual resting blood pressure.
Dietary Nitrates and Going Even Lower
If your blood pressure is already 108/73 and you are consuming foods or supplements known to lower blood pressure, you may want to be aware of the cumulative effect. Dietary nitrates, found in beets and dark leafy greens, have a real and measurable blood-pressure-lowering effect. A study on chronic beetroot juice supplementation found that it reduced systolic pressure, diastolic pressure, and vascular resistance both at rest and during exercise compared to a nitrate-depleted placebo version of the same juice.10PubMed. Effects of chronic dietary nitrate supplementation on the hemodynamic response to dynamic exercise
For someone with high blood pressure, that effect is desirable. For someone already sitting at 108/73, the additional drop could potentially push readings into territory where symptoms like lightheadedness become noticeable, especially during exercise when blood is being redirected to working muscles. This does not mean you should avoid vegetables. The effect from whole foods is modest. But concentrated beetroot juice supplements, high-dose garlic extract, and similar products marketed for cardiovascular health can add up, particularly if you are also taking medications that lower blood pressure. If you feel fine, there is no problem. If you notice dizziness or fatigue after starting a new supplement, your already-low baseline blood pressure is a reasonable suspect.
When It Is Worth Mentioning to a Doctor
A reading of 108/73 does not call for a doctor visit on its own. It calls for attention only in combination with other factors. These are the situations where it makes sense to bring up the number:
- New symptoms: Persistent dizziness, especially when standing, chronic fatigue that is not explained by sleep quality, frequent lightheadedness, or episodes of near-fainting.
- Recent medication changes: If you were recently started on a blood pressure drug, a diuretic, an antidepressant, or another medication that can lower blood pressure as a side effect, the reading provides useful information for dose adjustment.
- Existing heart disease: As discussed with the J-curve, people with coronary artery disease may need their diastolic pressure managed more carefully, and 73 is in the range that warrants a conversation.
- Significant drop from your baseline: If your blood pressure usually runs around 125/80 and has recently dropped to 108/73 without an obvious explanation like increased exercise or weight loss, the change itself is worth investigating even though the new number looks fine on paper.
For the vast majority of adults, especially younger and middle-aged people without cardiovascular disease, 108/73 is simply a healthy blood pressure reading. The cardiovascular system has robust mechanisms to keep organs well-perfused across a wide range of pressures, and 108/73 falls well within that range. The body adjusts vascular tone, heart rate, and fluid balance to maintain adequate blood flow, and these regulatory systems operate efficiently at this pressure in most individuals. The number is worth tracking over time and interpreting in context, but it is not worth losing sleep over.