Causes and Risk Factors of Low Blood Pressure

Many things can cause your blood pressure to be too low (less than 90/60 millimeters of mercury, or mmHg—what's referred to as hypotension). It can be due to factors that are not related to an underlying disease, such as dehydration or medication side effects. But it may also be the result of issues such as heart problems, hormone disturbances, neural conditions, and even pregnancy.

Determining what's at the root of your low blood pressure starts with figuring out the exact kind of hypotension you have.

Common Causes

The three main types of low blood pressure are orthostatic hypotension, neurally mediated hypotension, and severe hypotension linked to shock. Each has different causes.

Orthostatic Hypotension

One especially important cause of low blood pressure is orthostatic hypotension, which is sometimes referred to as postural hypotension. This phenomenon happens when blood pressure drops rapidly during changes in body position, usually when changing from sitting to standing. When this condition is present, it causes the classic signs that the blood pressure is too low, like dizziness, blurry vision, and fainting.

Normally, your nerve receptors signal when you are rising and your central nervous system responds by telling the muscles in the walls of your arteries to contract to increase your blood pressure, as well telling your heart to beat faster. This keeps the blood from pooling in the lower portion of your body.

In orthostatic hypotension, that doesn't happen as it should, and blood pooling results in less blood reaching your brain, lower blood pressure, and wooziness.

Orthostatic hypotension can be caused by these conditions:

• Pregnancy
• Dehydration (which can be due to sweating, not drinking enough, vomiting, or diarrhea)
• Older age
• Heart conditions
• Anemia
• Severe infections
• Thyroid disorders
• Low blood sugar and diabetes
• Pulmonary embolism
• Nervous system disorders including Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, Guillain-Barré syndrome, and neuropathy

Orthostatic hypotension may also be a side effect from certain medications, especially diuretics or other high blood pressure medications, like beta blockers. Medicines used to treat erectile dysfunction and certain psychiatric disorders can also cause low blood pressure.

You may also experience orthostatic hypotension simply by being out in the heat or being immobile for a long period.

Neurally Mediated Hypotension

Problems with the nervous system—especially disorders of the autonomic nervous system, including postural orthostatic tachycardia syndrome (POTS) and vasovagal syncope—can cause low blood pressure after extended periods of standing. Emotional stress can also be a trigger of neurally mediated hypotension.

In these conditions, there is poor communication between your brain and your heart, sending false signals that your blood pressure is high. In turn, your heart slows, which drops your blood pressure further.

Autonomic neuropathy and peripheral neuropathy, which are characterized by nerve damage and can be caused by diseases like diabetes, also affect the regulation of blood pressure.

Severe Hypotension Related to Shock

While some of the causes of severe hypotension in shock may also cause orthostatic hypotension, the blood pressure drop is much more severe with the former—and it doesn't return to normal.

The causes of hypotensive shock include:

• Major blood loss (internal or external)
• Septic shock from infection or toxins
• Severe fluid loss from diarrhea, burns, or overuse of diuretics
• Cardiogenic shock due heart attack, arrhythmia, or pulmonary embolism
• Vasodilatory shock seen in head injury, liver failure, poisoning, or anaphylaxis.

Genetics

For the most part, having low blood pressure is a good thing. Unless it occurs suddenly or produces symptoms, there is usually nothing to worry about. In fact, when you have low blood pressure, you have a reduced risk of developing heart disease, having a heart attack, or experiencing a stroke.

A study conducted by a team of researchers at Howard Hughes Medical Institute found that a small portion of the population has a gene mutation that not only gives them lower blood pressure but also lowers their risk of heart disease, kidney disease, and stroke. In fact, according to the researchers, people who carry the mutation have a 60% reduction in developing hypertension, or high blood pressure, by the time they are 60 years old.

A 2012 study looked at gene variants that were associated with blood pressure and did not find that they had much influence on whether or not a person had orthostatic hypotension. While orthostatic hypotension is seen more often in people who have close relative with the condition, it hasn't been linked to specific inheritance patterns.

Cardiovascular

Sometimes your blood pressure is impacted by the function or structure of your heart. This can lead to orthostatic hypotension or, in severe cases, to cardiogenic shock. Here are some common issues that impact your blood pressure:

• Heart problems that cause low heart rate
• Heart issues resulting in diminished heart strength
• A decrease in the amount of blood supplied to the body

The buildup of plaque in your arteries that comes with aging narrows them and can reduce the blood flow to your heart and brain. This can also contribute to hypotension.

Lifestyle Risk Factors

Blood pressure can be impacted by other factors, including your diet, exercise, and age. Here is an overview of some additional risk factors for low blood pressure:

• Deficiencies of essential nutrients, such as folic acid or iron, can cause the number of red blood cells or the concentration of hemoglobin to decrease, resulting in anemia.
• Alterations in blood sugar, like those caused by diabetes, can lead to hypotension.
• Eating habits: Some older patients, especially those with existing high blood pressure, can experience postprandial hypotension, where the blood pressure drops suddenly after eating a large meal.
• Hydration: Be sure to drink appropriate amounts of water and/or sports drink when exercising to prevent dehydration. For longer periods of exertion or when you are sweating more, you need to replenish salt (electrolytes, as found in sports drinks) as well to maintain good blood pressure.

A Word From Verywell

Feeling a little woozy when you stand up suddenly is something most people experience occasionally. But if it happens frequently, it may be a concern. If you have been diagnosed with low blood pressure and start to experience symptoms such as dizziness, lightheadedness, fatigue, or fainting, you should talk with your healthcare provider right away.