Winter Hydration: Why Milk Retains More Fluid Than Water
TL;DR
- In a 2016 study comparing 13 beverages using the Beverage Hydration Index (BHI) at two hours, skimmed milk (1.58), oral rehydration solution (1.54), and whole milk (1.50) retained significantly more fluid than plain water (1.00), while tea and coffee hydrated comparably to water.
- After exercise-induced dehydration in the heat, participants who rehydrated with milk produced roughly 611 ml of cumulative urine (550 ml for milk with added sodium), compared with 1,184 ml for plain water and 1,205 ml for a sports drink.
- Drinking large volumes of plain water temporarily dilutes the blood and reduces vasopressin, increasing urination, whereas milk supplies lactose, protein, sodium, and potassium that slow gastric emptying and support fluid retention.
- Replacing mineral-rich water or milk during winter with large thermoses of tea brewed from very-low-mineral water can reduce dietary calcium, magnesium, and potassium intake even when total fluid volume increases.
- Warm milk with honey, salted homemade broths and stews, mineral-rich spring water, orange juice, and A2 cow or goat milk (for people sensitive to A1 beta-casein) offer nourishing cold-weather hydration options.
Key facts
- Beverage Hydration Index (BHI) at two hours after drinking 1 liter over 30 minutes: skimmed milk scored 1.58, oral rehydration solution 1.54, and whole milk 1.50, each retaining significantly more fluid than plain water at the 1.00 reference value.
- Cumulative urine output after post-exercise rehydration in the heat: approximately 611 ml with milk and 550 ml with sodium-added milk, versus 1,184 ml with plain water and 1,205 ml with a conventional sports drink.
- Fluid retention after heat-induced dehydration: humans retained approximately 51% of lost fluid when rehydrating with plain water, compared with 71% when rehydrating with sodium replacement.
- Specialized post-exercise oral rehydration solution concentration: approximately 60 mmol of sodium per liter improved fluid retention after exercise compared with water and a sports drink, though it did not improve subsequent cycling performance.
When colder days arrive, many people naturally replace cold drinks with large thermoses of hot tea. And while tea can offer plenty of benefits, there's something worth knowing: not all fluids hydrate equally, and drinking more doesn't necessarily mean retaining more.
Why does drinking large volumes of plain water trigger rapid urination?
Your kidneys continuously regulate how much water your body keeps.
When you drink large amounts of plain water, your blood becomes temporarily more diluted. This reduces vasopressin, a hormone that helps your kidneys conserve water.
The result is increased urination.
Electrolytes and nutrients influence this process, helping explain why different drinks can produce surprisingly different results.
How does milk compare with plain water, sports drinks, and tea in human hydration studies?
In a study comparing 13 everyday beverages, researchers gave participants equal amounts of different drinks and measured how much fluid their bodies retained.
The results were surprisingly different:
- Whole and skimmed milk retained significantly more fluid than plain water.
- Skimmed milk ranked highest numerically, closely followed by oral rehydration solution and whole milk.
- Tea and coffee provided hydration comparable to plain water.
- Orange juice also showed an early fluid-retention advantage.
Another experiment found that milk helped people retain substantially more fluid after exercise-induced dehydration than plain water.
A more recent human study confirmed that milk could remain in the body longer than water, fruit juice and sports drinks in younger adults.
Milk's advantage makes physiological sense. It contains protein, carbohydrates and electrolytes that influence digestion and fluid regulation.
How can drinking mostly low-mineral hot tea in winter lower calcium and electrolyte intake?
Different teas offer useful plant compounds, from increased alertness to relaxation, depending on the variety.
But several large cups prepared with very-low-mineral water provide little calcium or magnesium.
Large fluid loads also increase urine production and can alter urinary electrolyte excretion. This makes mineral balance particularly relevant when your diet already supplies insufficient minerals.
And although you generally sweat less during winter, your nutritional needs remain.
Fortunately, some of the most enjoyable cold-weather options also provide substantial nourishment:
- Warm milk with honey combines fluid, protein, calcium, potassium and carbohydrates.
- Homemade broths and hearty stews provide water alongside sodium, protein and other nutrients.
- Mineral-rich spring water, including sparkling varieties, can contribute meaningful calcium and magnesium.
- Orange juice supplies water, potassium, natural sugars and vitamin C.
For people sensitive to conventional cow milk, A2 cow milk or goat milk may offer better digestive tolerance due to differences in their beta-casein proteins.
How should you balance hot tea with mineral- and nutrient-rich drinks in winter?
Enjoy your tea. But when warm drinks start replacing most of your other beverages, it's worth paying attention to what those drinks actually provide.
Especially if your diet is already low in minerals, a little awareness of your fluid choices can make a meaningful nutritional difference.
Mineral-rich water, milk and nourishing warm meals can help maintain that balance throughout the colder months.
The composition of your drink matters, not just how much you consume.
The full article is linked in the first comment. It explores fluid retention, mineral balance, milk and A2 alternatives, orange juice, nourishing winter drinks, and a practical checklist.
The action plan
What the Beverage Hydration Index actually measures
The 2016 study by Maughan and colleagues compared 13 common beverages using the Beverage Hydration Index (BHI).
Healthy men consumed one liter of a test drink over 30 minutes. Researchers then measured urine production over four hours.
Water served as the reference value of 1.0.
At two hours, the index was:
- Skimmed milk: 1.58
- Oral rehydration solution: 1.54
- Whole milk: 1.50
- Plain water: 1.00
Higher values mean greater fluid retention relative to water. All three leading beverages performed significantly better than water, although their differences from one another were not established as significant.
This index reflects short-term fluid retention, rather than directly measuring how much water enters individual cells.
The design also matters. Drinking one liter within 30 minutes differs from sipping smaller amounts alongside meals.
A later human experiment found a similar milk advantage in younger adults, but not in older participants.
Milk after sweat-induced dehydration
A separate study examined recovery after exercise in the heat.
Participants replaced lost fluid using milk, milk with added sodium, water or a conventional sports drink.
Across the recovery period, cumulative urine output was approximately:
- Milk: 611 ml
- Milk with added sodium: 550 ml
- Water: 1,184 ml
- Sports drink: 1,205 ml
Both milk conditions also supported better net fluid balance.
This adds an important distinction to the resting beverage experiment. Milk's advantage was also observed when participants had actually lost substantial fluid through sweating.
It supports milk as a useful recovery beverage because it combines fluid with electrolytes, protein and carbohydrates.
Why milk can retain fluid longer
The nutritional composition of a drink influences how it moves through the digestive system.
Plain water generally leaves the stomach more quickly than energy-containing liquids.
Milk contains lactose, protein and, depending on the variety, fat. These can slow gastric emptying and change the rate at which fluid reaches the intestine.
Its sodium and potassium also contribute to normal fluid regulation.
These mechanisms help explain the observed retention advantage, although no experiment has precisely isolated how much each component contributes.
Whole and skimmed milk both performed well in the hydration studies. A higher fat content is therefore not required for milk's measured advantage.
Whole milk provides more dietary fat and energy. Skimmed milk provides much of the same protein, lactose and minerals with considerably less fat.
Mineral water: what the label actually tells you
Natural mineral waters vary widely in composition.
Some contain negligible amounts of calcium and magnesium. Others provide several hundred milligrams of calcium per liter and substantial magnesium.
This makes the mineral label more informative than descriptions such as natural, premium, still or sparkling.
The main distinctions are:
- Calcium: supports muscle contraction, nerve signaling and bone health.
- Magnesium: participates in energy metabolism, muscle function and enzyme activity.
- Sodium: contributes to extracellular fluid balance, especially after sweating.
- Bicarbonate: contributes to the mineral profile and buffering properties of certain waters.
Calcium and magnesium are particularly useful when evaluating water as a source of dietary minerals.
Sodium-rich rehydration solutions serve a different function. They are formulated to replace electrolytes and support fluid retention after significant losses.
A water rich in calcium and magnesium is not automatically equivalent to such a solution.
Carbonation itself does not establish greater hydration, but sparkling mineral water can provide substantial mineral intake.
Hard tap water may also contribute meaningful calcium and magnesium. Boiling can precipitate some calcium as limescale but does not eliminate all dissolved minerals.
The mineral balance question
Large water loads can increase urine production and alter the kidneys' handling of electrolytes.
In a small human experiment, rehydrating with plain water after heat-induced dehydration resulted in less retained fluid than rehydrating with sodium replacement.
Approximately 51% of the lost fluid was retained after plain water, compared with 71% in the sodium condition.
The kidneys regulate both water and mineral excretion. They can eliminate additional water while conserving electrolytes, so more urine does not necessarily mean proportionally greater mineral loss.
However, fluid-loading experiments have demonstrated changes in urinary electrolyte measurements. Animal experiments involving prolonged deionized-water intake have also reported disturbances in mineral balance.
These findings make mineral intake worth considering, especially when the diet already supplies too little.
The nutritional consequence of replacing mineral-containing beverages is more straightforward.
A person who previously obtained calcium and magnesium from mineral water, or calcium and potassium from milk, may lose those contributions when switching almost entirely to tea made with very-low-mineral water.
This matters even if total fluid intake stays unchanged or increases.
Orange juice: a different nutritional profile
Orange juice supplies water alongside carbohydrates, potassium and vitamin C.
Its carbohydrates provide energy, while potassium contributes to normal nerve and muscle function.
In the 2016 beverage experiment, orange juice showed greater fluid retention than water at two and three hours. The difference was no longer statistically significant after four hours.
Its most reliable everyday advantage over low-mineral water is therefore nutritional rather than a consistently demonstrated retention benefit.
Orange juice provides relatively little sodium. After substantial sweating, it does not replace sodium losses in the same way as a properly formulated rehydration solution.
Alongside adequate protein and sodium from food, orange juice can be a useful source of fluids, carbohydrates and potassium.
Warm milk with honey
Warm milk with honey combines the established nutritional properties of milk with additional carbohydrates.
Milk provides complete protein, calcium, potassium, sodium and lactose.
Honey contributes sweetness and readily available carbohydrate energy.
The result is a warm, nourishing beverage that can fit naturally into colder-weather routines.
The specific combination has not been tested against plain milk in beverage hydration trials, so its additional value is best attributed to the carbohydrate and energy contribution rather than a proven increase in fluid retention.
A2 casein and goat milk: digestive differences
People who experience discomfort from conventional cow milk may benefit from distinguishing lactose from milk-protein composition.
Beta-casein is a major milk protein with genetic variants, including A1 and A2.
Conventional cow milk commonly contains both forms. Certified A2 cow milk contains the A2 variant without A1.
Goat milk predominantly contains A2-type beta-casein, although its proteins have natural variation.
A1 beta-casein can release a peptide called beta-casomorphin-7 during digestion. Experimental research suggests that this peptide can interact with intestinal opioid receptors and influence digestive processes.
Several randomized human studies reported improvements in selected digestive symptoms with A2-only milk compared with conventional milk. More recent findings have been mixed, so better tolerance is not universal.
The practical distinctions are:
- Lactose-free cow milk: addresses difficulty digesting lactose.
- Certified A2 cow milk: changes the beta-casein composition.
- Lactose-free A2 milk: combines both properties.
- Goat milk: offers predominantly A2-type beta-casein but still contains lactose.
Goat milk and A2 cow milk are not automatically suitable for people with diagnosed cow-milk protein allergies.
These differences concern digestive tolerance. A2 milk has not been demonstrated to retain more fluid than conventional cow milk.
Broths, stews and nourishing soups
Warm meals can contribute both fluid and nutrients, with the exact benefits determined by their ingredients.
A salted broth supplies water and sodium.
Meat provides protein, while potatoes and vegetables contribute carbohydrates, potassium and other micronutrients.
Connective tissue can release gelatin during slow cooking, contributing amino acids such as glycine.
Bone broth is often promoted as mineral-rich, but calcium and magnesium concentrations vary and can be relatively modest.
Using bones does not guarantee substantial mineral extraction.
A hearty stew containing meat, broth, potatoes and other nutrient-rich ingredients often provides broader nourishment than thin bone broth alone.
These meals have not been directly compared with water in beverage hydration-index trials. Their strength is the combination of fluid, food and electrolytes in one preparation.
Tea: plant compounds and water quality
Different teas offer different effects depending on the plants and their active compounds.
Caffeinated teas can support alertness. Some herbal preparations contain compounds traditionally used for relaxation, digestive comfort or throat soothing.
Tea's botanical properties and its mineral content are separate considerations.
A tea prepared with low-mineral water generally contributes little calcium or magnesium. Water with higher mineral concentrations can change that contribution.
Long brewing and boiling do not automatically remove all minerals from the water.
Tea's hydration-index result was comparable to plain water, making it useful for ordinary fluid intake.
The relevant winter distinction is therefore what tea replaces in the diet, not simply the quantity consumed.
When winter fluid needs change
During colder months, reduced heat exposure and sweating often lower fluid-replacement needs compared with hot summer conditions.
Heavy winter clothing, exercise, indoor heating and dry air can alter those needs.
Someone spending most of the day indoors without significant sweating has a different hydration requirement from someone training hard or working outdoors.
This matters because the strongest sodium-rehydration evidence comes from substantial fluid loss.
An oral rehydration solution containing approximately 60 mmol of sodium per liter improved fluid retention after exercise compared with water and a conventional sports drink.
That was a specialized experimental formulation, not an everyday drinking target.
The same study did not show better subsequent cycling performance despite greater retention.
For ordinary daily life, regular meals and drinks generally provide fluid and electrolytes without a need for concentrated rehydration solutions.
Excessive fluid consumption during endurance exercise can become dangerous when blood sodium becomes too diluted.
Medical fluid or sodium restrictions take priority when prescribed.
The one-page recap
Winter drinking habits
- Tea: useful botanical effects vary by variety
- Low-mineral tea water: limited calcium and magnesium contribution
- Seasonal beverage changes: can change daily nutrient intake
- Ordinary winter conditions: often lower sweat losses
- Heavy exercise or warm clothing: additional fluid losses possible
- Fluid intake: volume and nutritional composition both matter
Beverage hydration evidence
- Beverage Hydration Index: short-term fluid retention relative to water
- Skimmed milk: BHI 1.58 at two hours
- Oral rehydration solution: BHI 1.54
- Whole milk: BHI 1.50
- Water: BHI reference 1.00
- Milk: greater retention in controlled studies
- Tea and coffee: comparable retention to water
- Orange juice: temporary retention advantage
- Older adults: milk advantage not established in one newer study
- Trial conditions: large standardized drinks, not ordinary all-day sipping
Mineral water
- Calcium-rich water: additional dietary calcium
- Magnesium-rich water: additional dietary magnesium
- Sodium-rich formulations: particularly relevant after substantial sweating
- Carbonated mineral water: useful when mineral-rich
- Hard tap water: potential calcium and magnesium contribution
- Low-mineral water: limited mineral contribution
- Labels: mineral concentrations matter
Milk and A2 alternatives
- Whole milk: protein, carbohydrates, minerals and fat
- Skimmed milk: lower fat, strong measured retention
- Warm milk with honey: additional carbohydrate energy
- A2 cow milk: no A1 beta-casein
- Goat milk: predominantly A2-type beta-casein
- Lactose-free milk: addresses lactose intolerance
- Lactose-free A2 milk: combines both distinctions
- Goat milk: still contains lactose
- Milk-protein allergy: requires separate assessment
Juices and nourishing warm meals
- Orange juice: potassium, carbohydrates and vitamin C
- Orange juice after heavy sweating: low sodium content
- Salted broth: fluid and sodium
- Meat-based soup: fluid and protein
- Hearty stew: protein, carbohydrates and minerals
- Gelatin-rich broth: amino-acid contribution from connective tissue
- Bone broth calcium: variable and often modest
Fluid and electrolyte regulation
- Vasopressin: regulates kidney water conservation
- Large water loads: increased urine production
- Urine volume: not a direct measure of mineral depletion
- Low dietary mineral intake: beverage composition becomes more relevant
- Heavy sweating: sodium and fluid replacement both matter
- Specialized rehydration solutions: for appropriate fluid-loss conditions
- Excessive endurance-exercise drinking: low blood-sodium risk
- Medical fluid or sodium restrictions: individualized guidance takes priority
Frequently asked questions
How does milk compare to plain water on the Beverage Hydration Index (BHI)?
In a randomized trial of healthy men comparing 13 drinks over two hours against plain water (set at 1.00), skimmed milk scored 1.58, oral rehydration solution scored 1.54, and whole milk scored 1.50, each retaining significantly more fluid than water.
How much less urine do people produce when rehydrating with milk vs. water after exercise?
Following exercise-induced dehydration in the heat, participants who rehydrated with milk produced about 611 ml of cumulative urine (550 ml when sodium was added to milk), compared with 1,184 ml for plain water and 1,205 ml for a commercial sports drink.
Does drinking regular tea or coffee dehydrate you compared to water?
At normal moderate intakes, hot tea and coffee scored comparably to plain water on the Beverage Hydration Index, though replacing milk or mineral-rich water with tea brewed from very-low-mineral water can reduce daily calcium and magnesium intake.
What are good winter hydration options if regular cow milk causes digestive discomfort?
Lactose-free milk, A2 cow milk, goat milk, salted homemade bone or vegetable broths, orange juice, and naturally mineral-rich spring waters provide fluid alongside electrolytes that support retention.
References
- Maughan et al. (2016). A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. The American Journal of Clinical Nutrition, 103(3), 717–723.
- Shirreffs et al. (2007). Milk as an effective post-exercise rehydration drink. British Journal of Nutrition, 98(1), 173–180.
- Rodriguez-Sanchez et al. (2023). A randomised trial to assess fluid and electrolyte balance responses following ingestion of different beverages in young and older men. European Journal of Applied Physiology, 123(10), 2331–2340.
- Watson et al. (2008). A comparison of the effects of milk and a carbohydrate-electrolyte drink on the restoration of fluid balance and exercise capacity in a hot, humid environment. European Journal of Applied Physiology, 104(4), 633–642.
- Calbet et al. (1997). Role of caloric content on gastric emptying in humans. The Journal of Physiology, 498(2), 553–559.
- Nose et al. (1988). Role of osmolality and plasma volume during rehydration in humans. Journal of Applied Physiology, 65(1), 325–331.
- Fan et al. (2020). Efficacy of ingesting an oral rehydration solution after exercise on fluid balance and endurance performance. Nutrients, 12(12), 3826.
- Bankir et al. (2017). Vasopressin: physiology, assessment and osmosensation. Journal of Internal Medicine, 282(4), 284–297.
- Udokang et al. (2005). Effect of volume loading with water, normal saline, palm wine and Lipton tea on urinary output, pH, specific gravity, sodium and potassium concentrations in human subjects. Nigerian Journal of Physiological Sciences, 20(1–2), 101–106.
- Drobnik et al. (2005). The estimation of the influence of deionized water on the basic electrolytes level in blood and urine of tested animals. Roczniki Państwowego Zakładu Higieny, 56(3), 283–289.
- Killer et al. (2014). No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLOS ONE, 9(1), e84154.
- Hew-Butler et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine, 25(4), 303–320.
- Brooke-Taylor et al. (2017). Systematic review of the gastrointestinal effects of A1 compared with A2 β-casein. Advances in Nutrition, 8(5), 739–748.
- Ramakrishnan et al. (2020). Milk containing A2 β-casein ONLY, as a single meal, causes fewer symptoms of lactose intolerance than milk containing A1 and A2 β-caseins in subjects with lactose maldigestion and intolerance: a randomized, double-blind, crossover trial. Nutrients, 12(12), 3855.
- Sun et al. (2016). Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows' milk. Nutrition Journal, 15, 35.
- Robinson et al. (2025). Lactase-treated A2 milk as a feasible conventional milk alternative: results of a randomized controlled crossover trial to assess tolerance, gastrointestinal distress, and preference for milks varying in casein types and lactose content. Nutrients, 17(12), 1946.
- Milan et al. (2018). Digestive responses to fortified cow or goat dairy drinks: a randomised controlled trial. Nutrients, 10(10), 1492.
- Zoghbi et al. (2006). Beta-casomorphin-7 regulates the secretion and expression of gastrointestinal mucins through a mu-opioid pathway. American Journal of Physiology-Gastrointestinal and Liver Physiology, 290(6), G1105–G1113.