The Science of Dairy: Does Hot Milk Have Less Calcium?

December 13, 2025 •

4 min read

A 2016 study found that boiling non-processed milk for ten minutes could reduce its calcium content by 10-14%, suggesting that heating milk does have an impact on its mineral composition. The question, "Does hot milk have less calcium?" is more complex than a simple yes or no answer, involving changes to mineral solubility and overall bioavailability, not just total quantity.

Quick Summary

Heating milk can cause a minor reduction in total calcium while significantly impacting its bioavailability through chemical changes like precipitation. The effect is most pronounced with boiling or ultra-high-temperature processing, which can also degrade heat-sensitive vitamins and alter protein structures.

Key Points

Slight Reduction in Total Calcium: Boiling milk can reduce the overall calcium content by a small percentage, but it does not destroy the mineral entirely.
Reduced Bioavailability: Excessive heat causes calcium phosphate to precipitate, making the calcium less soluble and harder for the body to absorb effectively.
Effect Varies with Temperature: Gentle warming or standard pasteurization has minimal impact on calcium, while boiling or ultra-high-temperature (UHT) processing has a more noticeable effect.
Other Nutrient Loss: High heat diminishes heat-sensitive B vitamins (especially B12, folate, and riboflavin), leading to a reduction in the milk's overall nutritional density.
Denatured Protein: Boiling alters the structure of whey protein. This can sometimes improve digestibility for those with sensitivities but also slightly reduces total digestible protein.
Re-boiling is Unnecessary: Repeatedly boiling pasteurized milk offers no additional safety benefits and only serves to degrade its nutrient content further.

The Science Behind Heat and Calcium in Milk

Milk contains a crucial component known as colloidal calcium phosphate, which is suspended within the casein micelles. These micelles are complex structures of proteins and minerals. When milk is exposed to heat, the stability of these micelles is disrupted. The delicate balance of soluble (ionic) calcium and insoluble (colloidal) calcium shifts. The solubility of calcium phosphate decreases as the temperature rises, causing some of the mineral to precipitate and settle out of the solution.

This precipitation is a key factor in why hot milk can have slightly different nutritional properties. While the total amount of calcium (if the sediment is consumed) might not change drastically, the form it takes does. This transformation from a soluble to a less soluble state can, in turn, affect the body's ability to absorb and utilize the mineral, a concept known as bioavailability.

Boiling vs. Pasteurization: The Impact on Nutrients

Not all heat treatments are created equal. The effects on milk's nutrient profile vary significantly depending on the temperature and duration of heating.

Standard Pasteurization (High-Temperature Short-Time)

Most commercially available milk undergoes pasteurization, typically heated to around 72°C (161°F) for 15 seconds. This process is designed to kill harmful bacteria with minimal impact on nutrients. Research indicates that standard pasteurization does not significantly change the vitamin or mineral content of milk, so there is little nutritional difference between cold, pasteurized milk and milk gently warmed to serving temperature.

Boiling and Severe Heat Treatment

Bringing milk to a full boil, especially for extended periods, has a more pronounced effect. Beyond the slight reduction in measurable calcium content noted in some studies, boiling also affects other vital nutrients. Heat-sensitive B vitamins, including B12, folate, and riboflavin, can be substantially diminished. For example, some studies have shown reductions of 25-36% in certain B vitamins after boiling.

Excessive heat also alters the structure of milk proteins, particularly the whey protein. While this denaturation can make the milk proteins easier to digest for some individuals with sensitivities, it also changes their nutritional state. Furthermore, severe heat can initiate the Maillard reaction, where sugars and proteins react, affecting flavor, color, and potentially decreasing the overall nutritional value and digestibility of proteins.

How Bioavailability is Affected

The key issue with heating milk to high temperatures is not the outright destruction of calcium but rather its decreased bioavailability. A study published in PubMed demonstrated that severely heat-treated milk (multiple sterilization cycles) resulted in lower apparent calcium absorption and retention in rats compared to UHT-treated milk. The researchers concluded that factors from thermal damage, such as Maillard reaction products, might negatively impact dietary calcium utilization. This suggests that while calcium is still present, the body may not be able to access it as effectively.

Practical Recommendations for the Kitchen

For most people, the nutritional differences between cold, pasteurized milk and warm milk are negligible. The choice is often a matter of personal preference or practical application. However, understanding the effects of different heat levels can help you make more informed decisions about milk preparation, especially if it is a major source of nutrients in your diet.

Here are some tips to preserve milk's nutritional integrity:

Avoid re-boiling pasteurized milk: There is no safety benefit to re-boiling milk that is already pasteurized, and it only serves to diminish its nutrient content unnecessarily.
Use gentle heat: When warming milk, use medium heat and remove it from the heat source as soon as small bubbles form around the edges. Avoid a rapid, rolling boil.
Don't discard the "skin": The skin that forms on boiled milk contains precipitated proteins and minerals, including calcium. While its texture is not for everyone, removing it means you are losing a portion of the milk's nutritional value.
Consider nutrient losses: If milk is a primary source of B vitamins in your diet, be mindful that excessive heating will reduce these. For most, milk's primary role is a source of calcium, protein, and Vitamin D, which are less sensitive to gentle warming.

Comparison of Cold vs. Boiled Milk


Feature	Cold Milk (Pasteurized)	Boiled Milk
Safety	Already safe to drink due to pasteurization.	Kills bacteria, but redundant for most store-bought milk.
Nutrient Retention	Retains all original vitamins and minerals.	Loses some heat-sensitive vitamins (B12, folate, riboflavin) and potentially affects bioavailability of minerals.
Protein Integrity	Protein structure remains intact and stable.	Whey protein is denatured; casein remains stable but may interact with whey.
Calcium State	Calcium is highly bioavailable in its soluble and colloidal forms.	Some calcium phosphate precipitates, reducing solubility and bioavailability.
Taste & Texture	Fresh, smooth taste.	Slightly different, cooked flavor and potentially a skin on top.
Digestibility	Good for most, but some with lactose sensitivity may struggle.	Denatured proteins may make it easier to digest for some.

Conclusion

While a gentle warming of pasteurized milk has a negligible effect, the answer to "does hot milk have less calcium?" becomes nuanced when we consider boiling. High heat can cause a minor reduction in total calcium and, more importantly, can reduce the mineral's solubility and bioavailability by causing calcium phosphate to precipitate. It also significantly depletes heat-sensitive B vitamins. For most consumers, the difference between hot and cold milk is about preference rather than a major nutritional trade-off. However, those relying heavily on milk for specific nutrients should be aware of these effects and consider using a gentle heating method to preserve its full nutritional profile.

Assessing the effects of severe heat treatment of milk on calcium utilization

Frequently Asked Questions

No, boiling milk does not destroy all the calcium. The mineral content is not eradicated but undergoes a chemical change where some calcium phosphate precipitates, becoming less soluble. This affects the bioavailability rather than the total amount.

Standard pasteurization (heating to 72°C for 15 seconds) has minimal effect on milk's nutrient profile, including calcium. Warming pasteurized milk gently at home also has negligible impact. The issues arise primarily with high-temperature boiling.

Reduced bioavailability means the body has a harder time absorbing and utilizing the calcium present in the milk. While the total amount is still there, less of it is available for building strong bones and teeth.

Yes, for some people. Warm milk can have a soothing effect on the digestive tract and may be easier to digest for individuals with sensitive stomachs. However, the nutritional content of cold versus gently warmed milk is largely the same.

To preserve milk's nutritional value, heat it slowly over medium heat and stop as soon as it reaches a gentle simmer, with bubbles forming around the edges. Avoid bringing it to a full, rolling boil.

While raw milk contains live enzymes and bacteria, it carries a significant risk of pathogens and foodborne illness. Pasteurization effectively kills these harmful microbes while largely preserving key nutrients, including calcium. The nutritional trade-offs of pasteurization are minimal compared to the safety benefits.

Boiling milk depletes heat-sensitive vitamins, particularly water-soluble ones like B12, folate, and riboflavin. One study noted reductions of 24% or more in B vitamins upon boiling.