Last year was the world’s ­fourth-hottest year on record. The United States felt the effect. Last summer, parts of the Midwest had record high temperatures. Those temperatures are expected to continue to rise.

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Although an association exists between higher temperatures and kidney stone risk, not all of the reasons are clear. But researchers predict that rising temperatures will mean higher numbers of kidney stone patients.

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In the United States, a half-million patients seek treatment for kidney stones in emergency rooms every year. Those numbers have been increasing in the past three decades. The same is true in Europe. The number of children with the condition has also increased.

How are they formed?

Kidney stones result when certain chemicals in urine concentrate and form crystals.

The crystals grow into larger particles (stones), which move through the urinary tract.

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If the stone gets stuck on its path and blocks the flow of urine, it can become painful and potentially dangerous.

Most stones are a combination of calcium and either oxalate or phosphorous.

Think of this process as putting Lego pieces together. Once you have one, you can stack another, and another, until you have a big piece, in this case a stone.

What increases the risks

Low urine volume is a major risk factor for kidney stone formation, because less fluid to dissolve urinary salts means more concentrated urine.

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Low volume of urine may be a result of dehydration, which could have different causes, including: not drinking enough fluids, strenuous exercise or time spent in a hot environment.

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You’ll know your urine volume is low when it turns a darker color.

Drinking more fluids is important in lowering your risks of forming stones — especially in already tropical and subtropical areas. Urologists call the Southeastern United States “the stone belt” because of the higher rate of stone formation across the region.

Obesity is also a major risk factor for stone formation. Being overweight can change the acid levels in urine and, consequently, increase your risk of stones.

Your diet is important, too. One high in animal protein such as beef, chicken, fish and pork may increase acid levels in the urine because meat breaks down into uric acid, which can help form stones.

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Other medical conditions — such as Crohn’s disease, ulcerative colitis, hyperparathyroidism — or other rare genetic disorders can make stones more likely to form. Some medications and high doses of vitamin C and calcium supplements may increase your risks.

Prevention tips

So, what can you do to prevent kidney stones?

For starters, increase your urine volume — in other words, drink a lot of water. This is especially true for people who have had stones before. I recommend my patients aim for six pints of water a day.

Citric acid may help prevent the formation of certain types of kidney stones. Adding lemon or lime to your water is a great way to get the extra citric acid. Lemonade is great but it usually contains a lot of sugar — so I generally discourage it.

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Other foods you may want to avoid: most kinds of nuts, beets, tea and, I’m very sorry to say — chocolate.

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Alas, these foods have high concentrations of oxalate that contribute to stone formation, especially in people prone to the condition. High urine oxalate levels aren’t always due to how much calcium you eat, but rather how much sodium you ingest. This is because salt keeps calcium from being reabsorbed from the urine into the blood.

I don’t ask my patients to limit their dietary calcium. Instead, I ask them to reduce their salt intake. You should also avoid soft drinks: most colas have high phosphate contents, which help create stones.

Left untreated, kidney stones can be deadly. If you are in pain and think you might have a kidney stone, go see a urologist for an exam.

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And remember, drink plenty of water and watch your diet this summer. As global warming increases, we will have to take care of our bodies, and the planet, progressively more.