The consumption of iced beverages is a common cultural practice, often sparking debate about its effects on health. Traditional practices, such as those in Chinese and Ayurvedic medicine, frequently advise against cold drinks, citing potential harm to the digestive system. Western science approaches this question with physiological measurement, seeking to understand the biological impact of introducing a cold substance into the body. Examining the scientific evidence allows for an objective assessment of what happens internally when you drink something very cold.
How Cold Temperatures Affect Digestion
The common belief that cold liquids slow down digestion stems from the idea that the body must expend significant effort to warm the fluid. While the body brings the liquid up to its core temperature of approximately 37°C (98.6°F), this process is rapid in healthy individuals. The stomach’s muscular walls and rich blood supply quickly warm the ingested fluid, causing the temperature to normalize within minutes.
Cold temperatures cause a transient physiological response in the gastrointestinal tract, primarily through vasoconstriction, which is the narrowing of blood vessels. This temporary reduction in blood flow can theoretically slow down gastric motility, or the movement of food. However, studies indicate that in healthy adults, cold water ingestion does not significantly impair the normal digestive process, including enzyme activity or nutrient absorption. For individuals with pre-existing conditions like achalasia, a disorder of the esophagus, very cold drinks can exacerbate symptoms, while warm liquids may provide relief.
Respiratory and Sinus Reactions to Cold Intake
Another concern is that cold drinks can cause congestion or make a person more susceptible to catching a cold. Scientific research confirms that cold beverages can trigger localized physiological responses in the upper respiratory system. When a cold liquid passes through the mouth and throat, it can cause temporary vasoconstriction in the mucosal lining of the nasal passages.
This chilling effect can lead to the temporary thickening of the mucus lining or, in sensitive people, a reflexive dilation of blood vessels that results in a runny nose, a phenomenon known as vasomotor rhinitis. For some individuals, especially those with asthma, the cold stimulus can irritate the throat and vagus nerve, potentially triggering a cough reflex or bronchospasm. While cold drinks can produce symptoms like congestion or a cough, there is no scientific evidence linking the ingestion of cold liquids to causing a viral infection, such as the common cold.
The sharp, sudden headache known as “brain freeze” or sphenopalatine ganglioneuralgia is a direct result of rapid temperature change near the palate. When a very cold substance touches the roof of the mouth, the body reacts by rapidly increasing blood flow to the area to warm it, causing the blood vessels to quickly expand. This sudden vascular change is sensed by the trigeminal nerve, which the brain interprets as intense, short-lived pain often felt in the forehead.
The Science of Thermoregulation and Energy Cost
The body maintains a stable core temperature around 37°C (98.6°F) through a process called thermoregulation. When a cold drink is consumed, the body must expend energy to bring the liquid up to this set point. This expenditure results in a measurable, though small, increase in metabolic rate, a process called water-induced thermogenesis.
The amount of energy expended is modest, estimated to be only about eight calories burned to warm a glass of ice water. This negligible energy cost means that drinking cold beverages is not a viable strategy for significant weight loss. During intense exercise, consuming cold fluids (around 4–10°C) can be beneficial, as it provides a direct cooling effect on the core temperature. This slight reduction can help delay heat-related fatigue and improve endurance, especially in hot environments.
Dental Sensitivity and Tooth Health Concerns
The most immediate effect of cold drinks is often felt in the teeth as a sharp, brief pain. This pain is due to dental sensitivity, which occurs when the protective enamel layer is worn down or when gums recede. This exposes the underlying dentin, a porous layer containing microscopic fluid-filled tubes that lead directly to the tooth’s nerve center.
When a cold liquid contacts this exposed dentin, the rapid temperature shift causes the fluid within these tubules to move, stimulating the nerve and resulting in a sudden jolt of pain. While the cold temperature itself does not damage healthy teeth, it highlights an underlying issue like enamel erosion, a cavity, or gum recession. The rapid contraction and expansion from temperature changes can also pose a minimal risk to existing dental work, such as fillings or crowns, or exacerbate small cracks in the enamel.