Low blood pressure can stem from a variety of causes, ranging from harmless physiological variations to serious medical conditions. While some people naturally maintain lower blood pressure without issues, others may experience hypotension due to factors that impact the heart’s ability to pump blood or alter blood vessel tone and volume. Identifying the cause is crucial for determining whether the hypotension is benign or indicative of an underlying health problem.
Common Causes
Genetic predisposition is one of the most benign causes. Many younger adults and athletes naturally have lower blood pressure due to better cardiovascular efficiency. Their hearts pump more effectively, and their arteries remain flexible. In these cases, low readings are typically not concerning if no symptoms are present.
Dehydration is another common cause. When the body loses more fluids than it takes in—through vomiting, diarrhea, fever, or insufficient intake—blood volume decreases. This can lead to dizziness, weakness, and fainting, especially when standing. Severe dehydration may lead to hypovolemic shock, a medical emergency requiring urgent care.
Blood loss, whether due to trauma, gastrointestinal bleeding, ruptured aneurysms, or heavy menstrual periods, can also lead to a significant drop in blood pressure. When blood volume reduces, the heart struggles to maintain adequate pressure, causing symptoms like pallor, rapid pulse, and confusion. This requires immediate medical attention.
Medication-Related Causes
Certain medications can cause low blood pressure. These include:
- Diuretics (e.g., furosemide, hydrochlorothiazide) which reduce fluid retention.
- Alpha-blockers (e.g., prazosin) and beta-blockers (e.g., atenolol), which relax blood vessels or slow heart rate.
- ACE inhibitors and angiotensin II receptor blockers (ARBs), which treat hypertension and heart failure.
- Antidepressants, particularly tricyclics, which may affect vascular tone.
- Parkinson’s disease medications like levodopa.
- Narcotic pain relievers and anaesthetics which cause vasodilation and reduced pressure.
Older adults are especially vulnerable to drug-induced hypotension due to polypharmacy (taking multiple medications). Monitoring and adjusting dosages can often resolve the issue.
Heart-Related Causes
Heart conditions can lead to low blood pressure, such as:
- Bradycardia (slow heart rate).
- Heart valve disease.
- Heart attack or heart failure.
These conditions impair the heart’s ability to pump blood effectively, leading to decreased arterial pressure. Symptoms such as chest pain, shortness of breath, or bluish skin (cyanosis) require urgent medical evaluation.
Endocrine Disorders
Endocrine issues are also common contributors to low blood pressure. These include:
- Addison’s disease, which affects the body’s ability to retain sodium and regulate vascular tone.
- Hypothyroidism, which slows heart rate and reduces vascular responsiveness.
- Diabetes, particularly when uncontrolled, may damage the autonomic nervous system, making it harder to regulate blood pressure.
Other Specific Causes
Postural (orthostatic) hypotension occurs when blood pressure drops significantly upon standing. It results from a delayed or inadequate autonomic response, which allows blood to pool in the lower extremities. Causes include dehydration, medications, and long periods of inactivity. This is common in older adults and can increase the risk of falls.
Postprandial hypotension occurs after meals, particularly in older adults. Blood is redirected to the digestive system, and if the cardiovascular system can’t adjust, blood pressure may fall, leading to dizziness or fainting. Smaller meals and avoiding large, carbohydrate-heavy meals can help.
Neurological disorders like Parkinson’s disease and multiple system atrophy impair the autonomic nervous system’s ability to regulate blood pressure. These conditions often cause chronic and difficult-to-treat hypotension.
Severe Infections and Allergic Reactions
Sepsis and severe infections trigger systemic inflammation and cause blood vessels to dilate, leading to septic shock. This life-threatening condition results in dangerously low blood pressure despite a high heart rate. Prompt treatment with fluids, vasopressors, and antibiotics is critical.
Anaphylaxis, a severe allergic reaction, also leads to profound hypotension due to vasodilation and fluid leakage from blood vessels. Without prompt treatment with adrenaline (epinephrine), anaphylactic shock can be fatal.
Rare Causes
In rare cases, nutritional deficiencies (e.g., vitamin B12 or folate) can cause anaemia, impairing oxygen transport in the blood and lowering blood pressure.
Pregnancy often causes a mild drop in blood pressure, particularly in the first and second trimesters, as blood vessels dilate to accommodate the developing fetus. While this is typically temporary and self-limiting, it should be monitored if symptoms like dizziness or fainting occur.
Conclusion
The causes of low blood pressure are diverse, ranging from harmless variations to life-threatening conditions. Identifying the cause is essential for effective treatment. Whether hypotension is medication-related, linked to an underlying illness, or part of a broader systemic condition, understanding the cause helps clinicians provide targeted care. It also enables individuals to manage their risk and seek appropriate medical attention when needed.
