Cold water is not bad for most healthy people. Drinking it won’t damage your organs, cause disease, or meaningfully slow your digestion in ways that matter day to day. That said, cold water does produce real, measurable physiological effects, and for a small number of people with specific conditions, it can genuinely make symptoms worse. Here’s what actually happens in your body when you drink it.
What Cold Water Does to Your Stomach
Your stomach contracts rhythmically to break down food and push it forward. Cold water temporarily slows those contractions. In a controlled study of healthy young men, drinking 500 ml of near-freezing water (2°C) significantly reduced the frequency of stomach contractions compared to body-temperature water (37°C), and that difference persisted for a full hour. Cold water also empties from the stomach more slowly than warm water.
For most people, this is barely noticeable. Your body warms the water quickly, contractions return to normal, and digestion proceeds. But the study also found that cold water before a meal reduced how much food participants ate afterward. If you’re trying to eat less, that’s potentially useful. If you’re already struggling to eat enough, it could work against you.
The Calorie-Burning Claim
You may have heard that cold water burns extra calories because your body has to warm it up. This is technically true and practically meaningless. Drinking 500 ml of water increases metabolic rate by about 30% for roughly 30 to 40 minutes. That sounds impressive until you see the actual numbers: about 100 kilojoules per 500 ml, or roughly 24 calories. Even if you drank two liters of cold water a day, the extra burn adds up to around 95 calories, less than a single banana.
Cold water can support weight management as one small piece of a larger picture, but it will never substitute for changes in diet or physical activity. Anyone selling cold water as a weight loss strategy is overstating the science considerably.
Cold Water and Headaches
If you’ve ever gotten a sharp headache from gulping ice water, you’re not imagining it. In a study of 669 women, 7.6% developed a headache after drinking just 150 ml of ice-cold water through a straw. Women with active migraines (at least one attack in the past year) were twice as likely to get one of these cold-stimulus headaches compared to women who had never had migraines. The headaches are typically brief and resolve on their own, but they’re worth knowing about if you’re migraine-prone. Drinking cold water more slowly tends to reduce the risk.
Effects on Your Heart Rate
Drinking ice water activates the vagus nerve, which runs from your brainstem to your abdomen and helps regulate heart rate. In healthy volunteers, 250 ml of ice water measurably slowed heart rate compared to room-temperature water. The effect was driven by increased vagal tone, essentially your body’s “rest and digest” branch of the nervous system kicking into higher gear.
For healthy people, this slight dip in heart rate is harmless and temporary. Researchers have raised questions about whether this matters for people with certain cardiac conditions, but the study itself was conducted in healthy subjects. The takeaway is that ice water does briefly nudge your cardiovascular system, just not in a way that poses a risk to most people.
Nasal Congestion Gets Worse, Not Better
One area where cold water performs noticeably worse than warm water is nasal congestion. In a classic study measuring how fast mucus moves through the nose, cold water actually slowed nasal mucus velocity from 7.3 mm per minute down to 4.5 mm per minute. Hot water did the opposite, increasing mucus velocity from 6.2 to 8.4 mm per minute. Hot chicken soup performed even better, reaching 9.2 mm per minute.
All the hot-liquid improvements faded by 30 minutes, but the cold water slowdown also persisted at that mark. If you’re congested from a cold or allergies, reaching for warm or hot fluids will help clear your nose more effectively. Cold water may temporarily thicken things up.
When Cold Water Is Actually Beneficial
During exercise, cold water has a clear advantage. In a study comparing cold and room-temperature water during a workout combining strength and cardio training, people drinking cold water had a significantly smaller rise in core body temperature: 0.83°C versus 1.13°C. They also delayed the onset of that temperature rise. With room-temperature water, core temperature climbed significantly after just 15 minutes. With cold water, that increase was delayed until 45 minutes.
Both groups drank similar amounts of fluid and experienced similar drops in hydration, so the benefit came specifically from the cooling effect of the water itself. If you’re exercising in warm conditions or doing prolonged physical work, cold water helps your body manage heat more effectively.
Who Should Actually Avoid Cold Water
For a few specific groups, cold water creates real problems. People with achalasia, a condition where the esophagus has trouble moving food into the stomach, are the clearest example. Cold water increases the resting pressure of the lower esophageal sphincter (the valve between your esophagus and stomach) and prolongs the duration of esophageal contractions. In practical terms, it makes swallowing harder. In one study, 9 out of 12 achalasia patients reported discomfort from cold food or drinks, including worsened difficulty swallowing, regurgitation, and chest pain.
People with other esophageal motility disorders may experience similar effects. Cold temperatures essentially tighten and slow the esophagus, which is fine when everything works normally but painful when the system is already struggling.
Cold water can also trigger sharp tooth pain if you have dentin hypersensitivity, where the protective enamel layer has worn down and exposed the underlying dentin. The cold stimulus causes rapid fluid movement through tiny tubes in the tooth, activating pain receptors. This isn’t dangerous, but it’s a sign of enamel erosion worth addressing with a dentist.
Why the Myth Persists
Traditional medical systems, particularly Ayurveda and traditional Chinese medicine, have long advised against cold water. Ayurvedic teaching holds that cold water increases mucus production and disrupts digestion, while warm water supports the body’s natural balance. These systems developed their recommendations through centuries of observation, and some of their claims (like cold water thickening nasal mucus) do align with modern findings. Others, like the idea that cold water “extinguishes digestive fire,” don’t map neatly onto what we can measure physiologically.
The real answer is undramatic. Cold water produces temporary, modest changes in stomach motility, heart rate, nasal mucus flow, and esophageal pressure. For the vast majority of people, these changes are trivial and resolve within minutes to an hour. The most important thing about water isn’t its temperature. It’s that you’re drinking enough of it.