Hydration: The Effectiveness of Different Beverages
Different beverages affect the body’s hydration levels in different ways. To evaluate this effect, researchers use the Beverage Hydration Index (BHI), which reflects how long fluid is retained in the body compared to water.
Beverages with hydration levels equal to or close to water include:
Water — the baseline standard (≈100%).
Tea and coffee — approximately 90–100%.
Despite containing caffeine, moderate consumption does not cause significant dehydration.
Milk — may exceed 100% (≈110–130%).
The higher hydration effectiveness of milk is due to:
the presence of proteins and fats;
its electrolyte content (especially sodium and potassium);
slower fluid elimination from the body.
Note: Values above 100% do not mean additional water intake, but rather more efficient fluid retention in the body.
Fruits and vegetables contain a high percentage of water (about 80–95%), including:
cucumbers;
watermelon;
oranges.
They:
contribute to overall hydration;
are a beneficial addition to the diet.
However, they cannot fully replace drinking water because:
the amount consumed is limited;
water is absorbed more slowly.
Recommendation: Use water-rich foods as an additional source of hydration.
Alcohol has a pronounced diuretic effect.
Mechanism:
suppresses the production of vasopressin (antidiuretic hormone);
reduces water reabsorption in the kidneys;
increases fluid loss from the body.
Consequences:
the body loses more fluid than it gains;
the risk of dehydration increases.
Therefore, it is inaccurate to consider alcohol as beneficial for hydration, even if the beverage contains water.
Standard serving sizes:
beer — approximately 12 oz (355 ml);
wine — approximately 4 oz (125 ml);
spirits — 1.5–1.7 oz (40–50 ml).
Recommendation: Alternate alcohol with water (e.g., a 1:1 ratio) to reduce the risk of dehydration.
Caffeine has a mild diuretic effect; however:
at typical intake levels (up to about 300–400 mg per day),
it does not cause clinically significant dehydration;
the body partially adapts to its effects.
Examples of caffeine content:
black tea — about 40–50 mg per 8 oz (250 ml);
coffee — about 80–100 mg per 8 oz (250 ml).
As a result, tea and coffee can be counted toward daily fluid intake.
The most effective approach to maintaining hydration includes:
Foundation: plain drinking water;
Additional sources:
tea;
coffee;
milk;
water-rich foods;
Limit: alcoholic beverages.
A balanced combination of different fluid sources is key to maintaining optimal hydration levels.
More details: https://www.nhs.uk/live-well/eat-well/food-guidelines-and-food-labels/water-drinks-nutrition/