Q&A: How Dehydration Leads to Dizziness and Low Blood Pressure
Could you discuss the connection between dizziness and dehydration, and how it affects your blood pressure?
—Michell
As an OT, blood pressure dysregulation is one of the most common challenges I face on a day-to-day basis. While it’s mostly hypertension (high blood pressure), hypotension is often an issue as well, and often as a result of dehydration.
Today, I’ll go in depth to answer Michell’s question by delving into the biological mechanisms of how dehydration impacts blood pressure, how it leads to dizziness, and practical tips for preventing dehydration.
Dehydration, Dizziness, & Hypotension
Water is crucial for many physiological functions, including digestion, nutrient transportation, and thermoregulation (temperature control). The human body is composed of about 60% water, and much of that water is found in the intracellular fluid (inside cells) and the extracellular fluid (outside the cells, including blood plasma). When you become dehydrated, there is a reduction in the extracellular fluid volume, which includes a decrease in blood plasma.
As a result, blood volume decreases, meaning there’s less fluid to be pumped by the heart to supply oxygen and nutrients to tissues. Blood pressure is determined by the force exerted by blood against the walls of blood vessels. When blood volume drops, the body compensates by constricting blood vessels to maintain blood pressure, but this is a temporary fix. The heart then has to pump harder, and the blood becomes thicker due to the reduced fluid content.
This thickened blood, or increased blood viscosity, reduces circulation efficiency, which can impair the function of organs like the brain, kidneys, and heart. This leads to symptoms like dizziness, lightheadedness, and fainting, especially when standing up quickly, a phenomenon known as orthostatic hypotension.
How Dehydration Leads to Low Blood Pressure (Hypotension)
When the body’s water balance is disrupted, several factors contribute to a reduction in blood pressure:
Decreased Plasma Volume: The plasma in your blood is primarily composed of water. When dehydration reduces plasma volume, it leads to hypovolemia (low blood volume), which decreases the amount of fluid available to circulate through the body. This, in turn, reduces blood pressure.
Vasoconstriction: As blood volume decreases, the body attempts to compensate by constricting blood vessels, a process regulated by the sympathetic nervous system. This temporary solution increases resistance in the blood vessels, which can maintain blood pressure for a short time. However, this doesn’t solve the underlying issue of decreased blood volume and can lead to chronic high blood pressure if left unchecked.
Impaired Kidney Function: The kidneys play a critical role in maintaining water balance and blood pressure. When dehydrated, the kidneys signal the body to retain as much water as possible, releasing the hormone renin. Renin activates the renin-angiotensin-aldosterone system (RAAS), which raises blood pressure by increasing sodium and water retention. While this helps temporarily, prolonged dehydration can overwhelm the kidneys, further impairing their ability to regulate fluid balance and blood pressure.
Thicker Blood: When your body is dehydrated, the blood becomes more concentrated, increasing its viscosity. This makes it harder for the heart to pump the blood efficiently, leading to increased strain on the cardiovascular system and the potential for poor circulation and dizziness.
The Mechanism of Dizziness and Orthostatic Hypotension
Orthostatic hypotension occurs when there is a sudden drop in blood pressure when standing up from a sitting or lying position. In a well-hydrated person, the body reacts quickly to this change in posture by increasing heart rate and constricting blood vessels to maintain blood flow to the brain and other organs. however, when dehydrated, these compensatory mechanisms are impaired, leading to a temporary lack of blood flow to the brain, causing dizziness, lightheadedness, or even fainting.
This occurs because:
The baroreceptors (pressure sensors in the blood vessels) don’t detect sufficient blood flow as the blood volume decreases.
The autonomic nervous system doesn’t respond quickly enough to the change in posture, leaving the brain and other organs without the oxygenated blood they need.
How to Prevent and Manage Dehydration-Induced Dizziness
Staying hydrated is the best way to maintain blood pressure and prevent dehydration-related dizziness. Here are some practical strategies to ensure proper hydration:
Drink Enough (and Not Too Much) Water: The "8-10 cups a day" guideline is a myth dating back to the 1940s and has since been misinterpreted. Your hydration needs are highly individualized, depending on factors like sex, height, activity level, and temperature. It’s more common to drink too much water than too little, which can lead to hyponatremia—a condition where low sodium levels in the blood cause swelling in cells, leading to dizziness, headaches, and even organ damage. Instead of following a fixed rule, listen to your body and drink water based on your specific needs, adjusting for temperature, exercise, and other personal factors.
Consume Enough Salt: While many restrict salt, it’s essential for proper hydration. Sodium helps your body absorb and retain water through osmosis, ensuring your cells stay hydrated. Without enough salt, you may experience low blood pressure, dizziness, and dehydration. Opt for high-quality sea salt, which contains beneficial minerals like magnesium and potassium to support hydration and balance. Remember, moderation is key—too much can be harmful, but not enough can impair your body's ability to retain water.
Incorporate Electrolytes: Electrolytes like sodium, potassium, calcium, and magnesium are essential for maintaining fluid balance. These are my favorite kinds, and here is why I avoid Gatorade and Pedialyte:
Best Electrolyte Powder: Redmond Re-lyte Electrolyte Powder, LMNT, and IQMix
Best Electrolyte Drink: Nooma Organic Electrolyte Sports Drink and Vita Coco Coconut Water
Best Electrolyte Tablet: Nuun Sport: Electrolyte Drink Tablets
Eat Hydrating Foods: Include water-rich foods such as cucumbers, watermelon, and oranges, which can help maintain hydration levels.
Be Aware of Caffeine and Alcohol: While caffeine and alcohol can have a diuretic effect, they only contribute to dehydration in proportion to how much you consume. If you drink coffee or alcohol, it's important to balance it with extra water to maintain proper hydration.
Monitor Urine Color: The color of your urine is a good indicator of hydration. Pale yellow or clear urine generally means you're well-hydrated, while dark yellow or amber indicates dehydration.
Gradual Postural Changes: If you feel lightheaded after standing up, try rising slowly. Allow your body time to adjust to the change in posture, which can help prevent dizziness and, worse, a fall.
Takeaway
Dehydration can cause dizziness by reducing blood volume, increasing blood viscosity, and impairing the body's ability to regulate blood pressure. The biological mechanisms behind dehydration-induced dizziness are closely linked to the circulatory system and the body’s hydration status.
Stay hydrated, get enough electrolytes, and consult a healthcare professional for advice.
If you have a question, shoot me an email at contact@mindbodydad.com.
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