Kidney stones in hot weather: what research says about heat, dehydration and drinking water

Do kidney stones show up more often when it is hot? Studies of kidney stones in hot weather say yes, with limits. The question of hot weather and kidneys is covered here through seven papers: three on heat and stones, one review of the causes, and three on whether drinking more water lowers the risk.

It is informational material, not medical advice. Pain you suspect comes from a kidney stone is a reason to see a doctor, not to read an article.

Kidney stones in hot weather: what the visit data show

The largest US study counted visits, not stones. Tasian and colleagues took 60,433 patients who sought evaluation or treatment for kidney stones in 2005–2011 (insurance claims data) in five cities: Atlanta, Chicago, Dallas, Los Angeles and Philadelphia (Tasian et al., 2014).

The link between temperature and visits was not a straight line, and its shape differed from city to city. In most of them, though, risk rose once the mean daily temperature passed 10 °C. Comparing a day averaging 30 °C with one averaging 10 °C, the cumulative relative risk over 20 days was:

• Atlanta: 1.38 (1.07–1.79)
• Chicago: 1.37 (1.07–1.76)
• Dallas: 1.36 (1.10–1.69)
• Philadelphia: 1.47 (1.00–2.17)
• Los Angeles: 1.11 (0.73–1.68), a result that cannot be told apart from no effect

In four cities the strongest link was with a lag of three days or less. Cold was tied to visits too: below 2 °C in Atlanta, below 10 °C in Chicago and Philadelphia.

Two cautions belong next to these numbers. A visit is the day someone sought care, not the day a stone formed. And a mean of 30 °C is a very hot day, so the 30-versus-10 comparison describes extremes, not an ordinary summer afternoon.

Are kidney stones more common in summer? Humidity changes the picture

Ross and colleagues looked at South Carolina, 1997–2015, 188,531 patients (Ross et al., 2018). Their starting point is physical: temperature and humidity push water loss by evaporation in opposite directions, and the authors call evaporation the likely mediator between temperature and stones.

In summer, the best predictor of visits was the daily wet-bulb temperature, a measure that takes both heat and humidity into account. On the hottest days (99th percentile) compared with the median day, the excess risk was 8–14%, depending on the metric. In winter the metrics worked about equally well. The authors conclude that the combination of temperature and humidity sets the risk, most of all in humid heat.

For what humid heat does to the body in general, see heat, humidity and fatigue. If you want a single figure for how hot and humid a given day feels, the site has a feels-like calculator. The studies above do not use it and do not say which feels-like value matters for stones.

Does hot weather cause kidney stones? What the review can and cannot say

Fakheri and Goldfarb reviewed the literature (Fakheri & Goldfarb, 2011). The cause of most kidney stones is unknown, they write, and the literature points to heat and climate as significant risk factors. Most of the studies are distorted by other factors, such as sunlight and regional differences in diet. Even so, heat appears to matter in certain groups, and its role is much larger in men than in women.

So the careful reading is an association. Hot days go with more stone visits. That is not the same as showing that heat forms stones in any given person. This article covers one slice of the question, heat and water. Most stones have other causes that nothing here addresses.

A projection sits on the same shelf. Brikowski and colleagues modelled the south-eastern US "stone belt" and estimated that the share of the US population in high-risk zones would grow from 40% in 2000 to 56% by 2050 and 70% by 2095, with 1.6–2.2 million more lifetime cases by 2050 under a moderate warming scenario (Brikowski, Lotan & Pearle, 2008). It is a model forecast, not something anyone has observed.

Dehydration and kidney stones: what drinking more water has shown

The heat studies suggest water loss as the bridge. The water studies test it from the other side. The first of them followed people who had already had a stone.

Borghi and colleagues followed 199 patients for five years after a first idiopathic calcium stone (Borghi et al., 1996). One randomly chosen group was told to drink a lot of water with no change in diet; the other had no treatment. A stone came back in 12 of 99 in the water group and in 27 of 100 in the other (p = 0.008). The mean time to recurrence was 38.7 against 25.1 months. At the start, patients with stones had less urine than a control group of 101 people: men 1,057 against 1,401 mL a day, women 990 against 1,239. The authors read this as urine volume being a real risk factor and a high water intake as the first step against recurrence.

A 2016 meta-analysis pooled nine studies: two randomized trials (269 patients) and seven observational ones (273,685 people) (Cheungpasitporn et al., 2016). High fluid intake went with a relative risk of stones of 0.40 (0.20–0.79) in the trials and 0.49 (0.34–0.71) in the observational studies. For repeat stones the figures were 0.40 and 0.20. Data on how well people stick to it and on safety were thin, and the authors suggest studying safety separately in people at risk of fluid overload or low blood sodium (hyponatremia).

The newest review, from 2026, covered 31 studies, 26 of them randomized (Asher et al., 2026). For adults with calcium oxalate or calcium phosphate stones, more water is among the measures that may lower recurrence, alongside diet changes and medications a doctor selects. The strength of evidence is low. For children, and for harms, there is little data.

How this fits with "drink when thirsty"

How much water you need argues that general water norms are population estimates, not a personal target, that heat and activity raise losses, and that for most people thirst is the best guide. Nothing here contradicts that. The studies above are about stopping stones from forming or coming back, including repeat stones in people who have already had one. For them, the amount of water is a conversation for the doctor, and more so with heart or kidney disease, where the meta-analysis itself raises fluid overload and hyponatremia. No litres or targets are given here because no paper above supports one for everybody.

What nobody knows yet

• How much heat itself, as opposed to diet, sunlight or region, adds to stone risk. The review says most studies are distorted by such factors.
• Why the effect of heat is much larger in men than in women. The sources do not explain it.
• Whether US findings hold elsewhere. The heat data here are mostly American, and mostly observational.
• When a stone formed. Visits show when someone sought care.
• How much water suits a given person. The evidence for water is about prevention, especially of repeat stones, and it is rated low or limited. No paper gives a target for everyone.

What the app can and cannot do

In MeteoHealth you set the daily water goal yourself, in steps of 100 mL between 1,000 and 4,000 mL. The field opens at 2,000 mL, which is a starting point and not a recommendation. The app does not derive the goal from weight, sex or age. Optionally, as a PRO feature that is off by default, it adjusts the goal for heat and activity and shows the breakdown: base, plus a weather adjustment, plus an activity adjustment. The app's own description of the feature says it "does not prescribe diets and does not judge your food. Calorie and hydration numbers are estimates from open data and your profile — not the advice of a nutritionist or doctor."

The app does not recognize or diagnose kidney stones. If you have had them, agree the water goal with your doctor and enter it yourself.