Here’s how lemon juice can keep the kidneys at bay

A surprising drug may explain how lemon juice puts pressure on kidney stones.

Lemons contain nanoparticles that, when trapped in mice, block stone formation, scientists report on 22 Dec Nano Letters. If the tiny bags do the same for humans, nanoparticles may one day offer a way to prevent kidney stones in people, says pharmaceutical scientist Hongzhi Qiao of Nanjing University of Chinese Medicine.

Lemon juice is a well-known home remedy for kidney stones, which crystallize with minerals and form a mass inside the kidneys.SN: 9/21/18). These rocky masses rattle around in the urinary tract, ripping and damaging tissues as they eventually pass out of the body (SN: 10/31/16). “There is, yes, pain,” said Jingyin Yan, a nephrologist at Baylor College of Medicine in Houston, who was not involved in the new study. Patients feel a sharp pain in the back, side or lower abdomen when they pass a stone, looking up. “People describe it as worse than a baby.”

Although some medications can help treat kidney stones, many end up needing surgery to remove them, says Thomas Chi, a urologist at the University of California, San Francisco, who was also not part of the study. People often use their kidneys to shape small pebbles, sometimes they are shaped like large stones. “I pulled out the stones the size of a fist.”

Therefore, prevention is key. Scientists already knew that the citric acid that sours their lemons can do the trick by binding the minerals that make up the stones. But drinking mouth-puckering lemon juice is not so convenient for patients, Qiao says.

A 2022 clinical trial found that kidney stone patients drank 120 milliliters — about half a cup — of lemon juice per day. Drinking loads of lemonade can cause dental problems, too. Chi patients will drink so much that the acidic liquid eats away at their teeth.

So Qiao and his colleagues looked for other, milder lemon-derived ingredients that would help prevent kidney stones. Inside edible and medicinal plants like ginseng, grapefruit and dandelion, his team found extracellular nanoparticle-like vesicles, tiny sacs filled with molecules including fat, protein and DNA.

The mice were fed a substance that promotes the growth of kidney stones. Those that were fed the lemon nanoparticles also developed smaller kidney stones (left) than the mice that were not fed the grape pouches (right).L. Zhang et al/Nano Letters 2023The mice were fed a substance that promotes the growth of kidney stones. Those that were fed the lemon nanoparticles also developed smaller kidney stones (left) than the mice that were not fed the grape pouches (right).L. Zhang et al/Nano Letters 2023

These nanoparticles are in the lemon juice too – and the team fed them to the mice which also ingested a substance that promotes the growth of kidney stones. The zesty particles slowed stone formation, Qiao and colleagues found. The finding of these particles suggests the development of calcium oxalate crystals, the most common cause of kidney stones. The particles can also soften the stones and make them less viscous, the team showed.

The new work challenges conventional wisdom on how lemon juice works to fight kidney stones, Chi says. Using lemon nanoparticles to treat humans is still a long way off, but the team says the results hold promise. “The faster you can find this in a human clinical trial, the better.”