No Thirst Doesn’t Mean You’re Hydrated: What’s the Link Between Blood Pressure and Dehydration?
In recent years, many middle-aged adults have focused on wellness by adopting healthier habits—cutting back on sugar and salt, eating balanced meals, getting enough sleep, and exercising regularly. While these changes are great for overall health, one basic need often gets overlooked: staying properly hydrated. What should you keep in mind about hydration? How does dehydration affect blood pressure? And when’s the best time to drink water?
For this issue, healthyD spoke with Dr. Jacky Chan Kit, a heart specialist, about the signs of dehydration, the best ways to stay hydrated, and how to choose the right sports drinks. Dr. Chan also shares specific advices for middle-aged and older adults, as well as those with chronic health conditions.
For this issue, healthyD spoke with Dr. Jacky Chan Kit, a heart specialist, about the signs of dehydration, the best ways to stay hydrated, and how to choose the right sports drinks. Dr. Chan also shares specific advices for middle-aged and older adults, as well as those with chronic health conditions.
Dehydration: 3 Key Warning Signs
Water is vital for life. Many people think dehydration only happens after intense, long workouts, but everyday activities—like working in air-conditioned offices or being out in hot weather—can also cause fluid loss. If you don’t replace adequate fluid, you can get dehydrated. Dr. Chan points out three key signs to watch for:
1. Dry Mouth and Thirst
Don’t wait until you’re thirsty to drink water—by then, you’re already dehydrated.
2. Urine Color
Urine isn’t just for flushing out toxins— it’s also a hydration indicator. Passing light yellow colored urine means you’re well-hydrated. Passing dark yellow or amber colored urine means you are dehydrated and you will need water ASAP.
3. Body Weight
Dehydration leads to a noticeable drop in weight. Every 1kg of acute weight loss after exercise or profuse sweating suggests acute fluid loss of of 1 litre.
Water is vital for life. Many people think dehydration only happens after intense, long workouts, but everyday activities—like working in air-conditioned offices or being out in hot weather—can also cause fluid loss. If you don’t replace adequate fluid, you can get dehydrated. Dr. Chan points out three key signs to watch for:
1. Dry Mouth and Thirst
Don’t wait until you’re thirsty to drink water—by then, you’re already dehydrated.
2. Urine Color
Urine isn’t just for flushing out toxins— it’s also a hydration indicator. Passing light yellow colored urine means you’re well-hydrated. Passing dark yellow or amber colored urine means you are dehydrated and you will need water ASAP.
3. Body Weight
Dehydration leads to a noticeable drop in weight. Every 1kg of acute weight loss after exercise or profuse sweating suggests acute fluid loss of of 1 litre.
Dehydration: Can Drinking Too Much or Too Little Be Harmful?
Drinking water after exercise helps prevent dehydration, but can chugging too much water too quickly be dangerous? Dr. Chan explains that overloading on water can throw off your body’s electrolyte balance, leading to hyponatremia (low sodium levels) or even water poisoning ¹.
On the other hand, not drinking enough also carries risks. Heavy sweating drains both water and sodium. If you don’t replace them quickly, dehydration can worsen, and in severe cases, blood pressure can drop suddenly—causing dizziness, fainting, or even shock.
Drinking water after exercise helps prevent dehydration, but can chugging too much water too quickly be dangerous? Dr. Chan explains that overloading on water can throw off your body’s electrolyte balance, leading to hyponatremia (low sodium levels) or even water poisoning ¹.
On the other hand, not drinking enough also carries risks. Heavy sweating drains both water and sodium. If you don’t replace them quickly, dehydration can worsen, and in severe cases, blood pressure can drop suddenly—causing dizziness, fainting, or even shock.
Dehydration: The Best Times to Drink Water, According to a Doctor
Dr. Chan says you shouldn’t rely on thirst alone to tell you when to drink. Instead, sip water steadily throughout the day. He recommends these key times for hydration around workouts:
• Before Exercise: Drink enough water until you feel the urge to pee—that’s a sign you’re well-hydrated.
• During Exercise: If you’re sweating heavily, take small, frequent sips to keep your performance up ².
• After Exercise: For workouts lasting over an hour (like marathons), dehydration is common. Drink enough to replace 100–120% of the weight you’ve lost. For example, if you lose 1 kg, drink 1 to 1.2 liters of fluid ¹.
Since sweat also drains electrolytes, Dr. Chan suggests using sports drinks in moderation. Look for ones with osmolarity similar to that of blood (isoosmolar fluid).
Dr. Chan says you shouldn’t rely on thirst alone to tell you when to drink. Instead, sip water steadily throughout the day. He recommends these key times for hydration around workouts:
• Before Exercise: Drink enough water until you feel the urge to pee—that’s a sign you’re well-hydrated.
• During Exercise: If you’re sweating heavily, take small, frequent sips to keep your performance up ².
• After Exercise: For workouts lasting over an hour (like marathons), dehydration is common. Drink enough to replace 100–120% of the weight you’ve lost. For example, if you lose 1 kg, drink 1 to 1.2 liters of fluid ¹.
Since sweat also drains electrolytes, Dr. Chan suggests using sports drinks in moderation. Look for ones with osmolarity similar to that of blood (isoosmolar fluid).
Dehydration in Older Adults: Chronic Dehydration Can Cause Hypernatremia
Seniors are at higher risk for dehydration. Dr. Chan has seen cases where elderly people living alone didn’t drink enough because of self neglect. Long-term chronic dehydration reduces blood volume, triggering the kidneys to release hormones that tighten blood vessels and retain sodium and water—which can raise blood pressure³.
Seniors are at higher risk for dehydration. Dr. Chan has seen cases where elderly people living alone didn’t drink enough because of self neglect. Long-term chronic dehydration reduces blood volume, triggering the kidneys to release hormones that tighten blood vessels and retain sodium and water—which can raise blood pressure³.
Research shows that staying hydrated helps control blood pressure. One study found that people who drank ≥6 cups of water a day had a 40% lower risk of high blood pressure than those who drank ≤1 cup daily ⁴. Another study showed that drinking more than five cups of water daily reduced fatal heart disease risk by 41% (women) to 54% (men) compared to those drinking less than two cups of water daily⁵.
However, seniors with heart or kidney problems need to watch their fluid intake. Too much water can overwhelm their bodies, worsening their condition. For severe heart failure patients, Dr. Chan recommends limiting fluids to 1.5–2 liters a day and tracking urine output, leg swelling, and body weight to adjust intake safely.
Hydration Tips for Seniors: Eat Well to Stay Hydrated
A healthy diet supports hydration. Dr. Chan recommends the Mediterranean diet—low in bad fats, cholesterol, and salt, but high in magnesium, potassium, calcium, protein, and fiber. Foods like veggies, nuts, fruits, and fish (tomatoes, bananas, blueberries, walnuts, cashews, salmon) help prevent high blood pressure. In the long-term, this diet may help lower blood pressure by *about 10 mmHg* ⁶. (Note: Kidney disease patients should check with their doctor before eating high-potassium foods because they have impaired kidneys potassium excretion.)
Dr. Chan adds that seniors can get fluids from foods while also nourishing their bodies. Caregivers should monitor salt intake, aiming for no more than 2,300 mg of sodium daily (the American Heart Association’s guideline). For those with high blood pressure, less than 1,500 mg of sodium a day is ideal—and under 1,000 mg sodium a day can help even more ⁷.
A healthy diet supports hydration. Dr. Chan recommends the Mediterranean diet—low in bad fats, cholesterol, and salt, but high in magnesium, potassium, calcium, protein, and fiber. Foods like veggies, nuts, fruits, and fish (tomatoes, bananas, blueberries, walnuts, cashews, salmon) help prevent high blood pressure. In the long-term, this diet may help lower blood pressure by *about 10 mmHg* ⁶. (Note: Kidney disease patients should check with their doctor before eating high-potassium foods because they have impaired kidneys potassium excretion.)
Dr. Chan adds that seniors can get fluids from foods while also nourishing their bodies. Caregivers should monitor salt intake, aiming for no more than 2,300 mg of sodium daily (the American Heart Association’s guideline). For those with high blood pressure, less than 1,500 mg of sodium a day is ideal—and under 1,000 mg sodium a day can help even more ⁷.
Post-Workout Hydration Tips for Seniors
With more seniors staying active, Dr. Chan advises that for light exercise, plain water is enough. If using sports drinks, avoid high-sugar or high-sodium options, since long-term use can increase the risk of obesity, diabetes, and heart disease.
Those with high blood pressure or heart failure should keep sodium under 2,300 mg a day (about 1 teaspoon of salt). Too much salt can raise blood pressure, strain the heart and kidneys, and worsen fluid retention or heart failure.
With more seniors staying active, Dr. Chan advises that for light exercise, plain water is enough. If using sports drinks, avoid high-sugar or high-sodium options, since long-term use can increase the risk of obesity, diabetes, and heart disease.
Those with high blood pressure or heart failure should keep sodium under 2,300 mg a day (about 1 teaspoon of salt). Too much salt can raise blood pressure, strain the heart and kidneys, and worsen fluid retention or heart failure.
References:
1. Racinais S, et al. Br J Sports Med 2023;57:8–25. doi:10.1136/bjsports-2022-105942
2. Judge LW, et al. J Hum Kinet 2021;79:111–122. doi:10.2478/hukin-2021-0065
3. Watso JC, Farquhar WB. Nutrients 2019;11(8):1866. doi:10.3390/nu11081866
4. Li S, et al. Front Public Health 2024;11:1280653. doi:10.3389/fpubh.2023.1280653
5. Chan J, et al. Am J Epidemiol 2002;155(9):827–833. doi:10.1093/aje/155.9.827
6. Whelton PK, et al. Hypertension 2018;71(6):1269–1324. doi:10.1161/HYP.0000000000000066
7. American Heart Association. How much sodium should I eat per day? Accessed April 1, 2025
1. Racinais S, et al. Br J Sports Med 2023;57:8–25. doi:10.1136/bjsports-2022-105942
2. Judge LW, et al. J Hum Kinet 2021;79:111–122. doi:10.2478/hukin-2021-0065
3. Watso JC, Farquhar WB. Nutrients 2019;11(8):1866. doi:10.3390/nu11081866
4. Li S, et al. Front Public Health 2024;11:1280653. doi:10.3389/fpubh.2023.1280653
5. Chan J, et al. Am J Epidemiol 2002;155(9):827–833. doi:10.1093/aje/155.9.827
6. Whelton PK, et al. Hypertension 2018;71(6):1269–1324. doi:10.1161/HYP.0000000000000066
7. American Heart Association. How much sodium should I eat per day? Accessed April 1, 2025
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