Dehydration Symptoms: Is Drinking 8 Glasses of Water Really Enough?
In today’s health-conscious cities, many people are hitting the gym, running trails, and staying active. But after a tough workout, what’s the best way to rehydrate? Plain water works for some, while others reach for sports drinks—but are these sugary, sodium-loaded beverages actually helping or hurting us? For those managing blood sugar or blood pressure, the answer might be surprising. We spoke with Dr. Enoch Wu, a Specialist in Endocrinology, Diabetes & Metabolism, to break down the science of hydration and what you should really be drinking.
Why Hydration Matters for Blood Sugar and Blood Pressure
Keeping your blood sugar and blood pressure in check is crucial for long-term health. Yet in Hong Kong, 1 in 10 adults has diabetes¹, and nearly 30% live with the “Metabolic Syndrome” – hypertension, hyperglycaemia and dyslipidemia²—many without even knowing it, since early stages often show no symptoms.
According to Dr. Wu, while genetics and age play a role, obesity is one of the biggest controllable risk factors of metabolic syndrome³. Excess calories lead to visceral fat accumulation, which throws off hormone balance and makes it harder for the body to regulate blood glucose and blood pressure. The problem could be further complicated by fluid and electrolytes loss after intensive exercise, as dehydration may further exacerbate disturbances in blood sugar and blood pressure.
Keeping your blood sugar and blood pressure in check is crucial for long-term health. Yet in Hong Kong, 1 in 10 adults has diabetes¹, and nearly 30% live with the “Metabolic Syndrome” – hypertension, hyperglycaemia and dyslipidemia²—many without even knowing it, since early stages often show no symptoms.
According to Dr. Wu, while genetics and age play a role, obesity is one of the biggest controllable risk factors of metabolic syndrome³. Excess calories lead to visceral fat accumulation, which throws off hormone balance and makes it harder for the body to regulate blood glucose and blood pressure. The problem could be further complicated by fluid and electrolytes loss after intensive exercise, as dehydration may further exacerbate disturbances in blood sugar and blood pressure.
The 8-Glasses Myth: How Much Water Do You Really Need?
We've all heard the old advice: Drink eight glasses of water a day. But hydration isn't one-size-fits-all. Studies suggest proper fluid intake may help stabilize blood pressure and blood sugar?-so how much is enough? Dr. Wu explains that a good baseline is 35 mL of water per kilogram of body weight per day. That means:
• A 150-pound (68 kg) person needs about 2.4 Liters (10 cups).
• Someone weighing 200 pounds (90 kg) or more might require over 3 Liters (12 cups).
You’ll need even more if you:
• Work outdoors
• Do high-intensity workouts
• Have a fever or Diarrhea
• Spend long hours in air-conditioned offices (which can dry you out faster)
We've all heard the old advice: Drink eight glasses of water a day. But hydration isn't one-size-fits-all. Studies suggest proper fluid intake may help stabilize blood pressure and blood sugar?-so how much is enough? Dr. Wu explains that a good baseline is 35 mL of water per kilogram of body weight per day. That means:
• A 150-pound (68 kg) person needs about 2.4 Liters (10 cups).
• Someone weighing 200 pounds (90 kg) or more might require over 3 Liters (12 cups).
You’ll need even more if you:
• Work outdoors
• Do high-intensity workouts
• Have a fever or Diarrhea
• Spend long hours in air-conditioned offices (which can dry you out faster)
The Dangers of Dehydration: More Than Just Thirst
Skip fluids after heavy sweating, and things can go downhill fast. Losing just 3% of your body’s water triggers dehydration, with symptoms like:
• Extreme thirst
• Headaches
• Dizziness
In severe cases, it can lead to shock—or even become life-threatening.
Skip fluids after heavy sweating, and things can go downhill fast. Losing just 3% of your body’s water triggers dehydration, with symptoms like:
• Extreme thirst
• Headaches
• Dizziness
In severe cases, it can lead to shock—or even become life-threatening.
3 Drinks That Can Make Dehydration Worse
Not all beverages hydrate equally. Some popular choices-like coffee, tea, and broth-based soups-might actually backfire:
• Coffee and tea contain caffeine, a diuretic that makes you lose more water.
• Soups and broths are often packed with sodium, which can increase urine output.
Not all beverages hydrate equally. Some popular choices-like coffee, tea, and broth-based soups-might actually backfire:
• Coffee and tea contain caffeine, a diuretic that makes you lose more water.
• Soups and broths are often packed with sodium, which can increase urine output.
The Problem with Sports Drinks
After a long workout, water alone might not cut it. Sweating drains electrolytes (sodium, potassium, magnesium), and drinking too much plain water can dilute your sodium levels—a dangerous condition called hyponatremia. That’s why many people grab sports drinks.
But Dr. Wu warns: Most sports drinks are loaded with sugar and sodium. While they do replace electrolytes, regularly consumption can:
• Spike blood sugar (especially risky for diabetics)
• Raise blood pressure (due to excess sodium)
Worse, research shows that just one sugary drink a day increases fatty liver disease risk by over 50%⁵. And while exercise does deplete sodium, most people already get more than enough from their diet—the WHO recommends no more than 2 grams of sodium per day⁶, and sports drinks can push you over that limit, straining your heart and kidneys.
After a long workout, water alone might not cut it. Sweating drains electrolytes (sodium, potassium, magnesium), and drinking too much plain water can dilute your sodium levels—a dangerous condition called hyponatremia. That’s why many people grab sports drinks.
But Dr. Wu warns: Most sports drinks are loaded with sugar and sodium. While they do replace electrolytes, regularly consumption can:
• Spike blood sugar (especially risky for diabetics)
• Raise blood pressure (due to excess sodium)
Worse, research shows that just one sugary drink a day increases fatty liver disease risk by over 50%⁵. And while exercise does deplete sodium, most people already get more than enough from their diet—the WHO recommends no more than 2 grams of sodium per day⁶, and sports drinks can push you over that limit, straining your heart and kidneys.
Who Should Avoid Sports Drinks?
If you’re watching your blood sugar or blood pressure, sugary sports drinks could undo your workout’s benefits. For example:
• Running 1 km burns ~60 calories
• But a 500 mL sports drink (~30g sugar, 135 kcal) cancels out 2 km of effort
Dr. Wu advises caution for people with:
• Diabetes
• High blood pressure
• Heart or kidney conditions
If you need more than water after exercise, look for:
• Sugar-free options (to avoid blood sugar spikes)
• Low-sodium formulas (if you have hypertension)
• Optimal osmolality (200–311 mOsm/L)⁹ (for faster absorption)
"Osmolality" (solute concentration in fluids) affects this—higher osmolality slows absorption⁷, and excess sugar raises osmolality, impairing hydration⁸. WHO recommends fluids with 200–311 mOsm/L for optimal electrolyte replenishment and absorption efficiency⁹.
If you’re watching your blood sugar or blood pressure, sugary sports drinks could undo your workout’s benefits. For example:
• Running 1 km burns ~60 calories
• But a 500 mL sports drink (~30g sugar, 135 kcal) cancels out 2 km of effort
Dr. Wu advises caution for people with:
• Diabetes
• High blood pressure
• Heart or kidney conditions
If you need more than water after exercise, look for:
• Sugar-free options (to avoid blood sugar spikes)
• Low-sodium formulas (if you have hypertension)
• Optimal osmolality (200–311 mOsm/L)⁹ (for faster absorption)
"Osmolality" (solute concentration in fluids) affects this—higher osmolality slows absorption⁷, and excess sugar raises osmolality, impairing hydration⁸. WHO recommends fluids with 200–311 mOsm/L for optimal electrolyte replenishment and absorption efficiency⁹.
The Bottom Line
Hydration isn’t just about quantity—it’s about quality. For most people, water is still the best choice. But if you’re sweating heavily, an electrolyte drink without excess sugar or sodium can help. And if you have health concerns? Talk to your doctor before reaching for any sport drinks.
Hydration isn’t just about quantity—it’s about quality. For most people, water is still the best choice. But if you’re sweating heavily, an electrolyte drink without excess sugar or sodium can help. And if you have health concerns? Talk to your doctor before reaching for any sport drinks.
References:
1. 智友站《糖尿病》，retrieved on 18 Feb, 2025
2. 衞生防護中心《高血壓》，retrieved on 18 Feb, 2025
3. 香港家庭醫學學院《最怕肥「高」》，retrieved on 18 Feb, 2025
4. Hakam N, Guzman Fuentes JL, Nabavizadeh B, et al. Outcomes in Randomized Clinical Trials Testing Changes in Daily Water Intake: A Systematic Review. JAMA Netw Open.2024;7(11):e2447621. doi:10.1001/jamanetworkopen.2024.47621
5. Zou Y, Yu M, Sheng G. Association between fasting plasma glucose and nonalcoholic fatty liver disease in a nonobese Chinese population with normal blood lipid levels: a prospective cohort study. Lipids Health Dis. 2020 Jun 20;19(1):145. doi: 10.1186/s12944-020-01326-3. PMID: 32563249; PMCID: PMC7306139.
6. 衞生防護中心《鹽（鈉）攝取與健康》，retrieved on 18 Feb, 2025
7. Mettler, S., Rusch, C., & Colombani, P.C. (2006). Osmolality and pH of sport and other drinks available in Switzerland. Schweizerische Zeitschrift für Sportmedizin und Sporttraumatologie. 54(3), 92–95 https://www.researchgate.net/publication/238768115_Osmolality_and_pH_of_sport_and_other_drinks_available_in_Switzerland
8. Sollanek, K. J., Kenefick, R. W., & Cheuvront, S. N. (2019). Osmolality of commercially available oral rehydration solutions: impact of brand, storage time, and temperature. Nutrients, 11(7), 1485 https://pubmed.ncbi.nlm.nih.gov/31261904/
9. World Health Organization. (2002). Reduced Osmolarity: Oral Rehydration Salts (ORS) Formulation. https://iris.who.int/bitstream/handle/10665/67322/WHO_FCH_CAH_01.22.pdf
1. 智友站《糖尿病》，retrieved on 18 Feb, 2025
2. 衞生防護中心《高血壓》，retrieved on 18 Feb, 2025
3. 香港家庭醫學學院《最怕肥「高」》，retrieved on 18 Feb, 2025
4. Hakam N, Guzman Fuentes JL, Nabavizadeh B, et al. Outcomes in Randomized Clinical Trials Testing Changes in Daily Water Intake: A Systematic Review. JAMA Netw Open.2024;7(11):e2447621. doi:10.1001/jamanetworkopen.2024.47621
5. Zou Y, Yu M, Sheng G. Association between fasting plasma glucose and nonalcoholic fatty liver disease in a nonobese Chinese population with normal blood lipid levels: a prospective cohort study. Lipids Health Dis. 2020 Jun 20;19(1):145. doi: 10.1186/s12944-020-01326-3. PMID: 32563249; PMCID: PMC7306139.
6. 衞生防護中心《鹽（鈉）攝取與健康》，retrieved on 18 Feb, 2025
7. Mettler, S., Rusch, C., & Colombani, P.C. (2006). Osmolality and pH of sport and other drinks available in Switzerland. Schweizerische Zeitschrift für Sportmedizin und Sporttraumatologie. 54(3), 92–95 https://www.researchgate.net/publication/238768115_Osmolality_and_pH_of_sport_and_other_drinks_available_in_Switzerland
8. Sollanek, K. J., Kenefick, R. W., & Cheuvront, S. N. (2019). Osmolality of commercially available oral rehydration solutions: impact of brand, storage time, and temperature. Nutrients, 11(7), 1485 https://pubmed.ncbi.nlm.nih.gov/31261904/
9. World Health Organization. (2002). Reduced Osmolarity: Oral Rehydration Salts (ORS) Formulation. https://iris.who.int/bitstream/handle/10665/67322/WHO_FCH_CAH_01.22.pdf
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