Today we’re talking about kidney stones – not a fun topic, particularly if you’ve ever had them. And, whether you’ve had them or not, you will want to do all you can to avoid either a recurrence or getting one for the first time. Did you know they are more prevalent in the summertime?

What is a kidney stone?

Kidney stones are hard, “stone-like” deposits that form in one or both kidneys when amounts of certain minerals and other constituents of the urine get to a high enough level that they precipitate out. An analogy would be if you mixed salt in a glass of water and there was so much salt that it didn’t all dissolve and some sank to the bottom of the glass. Although there are several types of kidney stones, by far the most common type is calcium oxalate, which accounts for 80 percent of kidney stones. Less common are calcium phosphate, uric acid, struvite, and cystine kidney stones. 

Kidney stones can go undetected if they stay put in the kidneys. However, when they venture out and travel down the ureter toward the bladder, that is a different story altogether. If they are too large to pass, then they may try to retreat back into the kidneys. While they are trying to migrate, you will know about them because you will experience pain of varying degrees depending on the size and how far they get. They can also become stuck in the ureter and cause excruciating “flank” pain in your kidney region of your lower back that can radiate down, even to your lower abdomen and thigh region. And even if they don’t get stuck and are small enough to pass, it’s likely they will be big enough to give you some serious grief, requiring pain remediation.

If they don’t pass on their own, ultimately, they will likely require removal. This is typically done by a procedure called lithotripsy, which uses high intensity sound waves to break up the stone into smaller pieces so it can pass through the ureter. But don’t think that once they are smaller, passing them is going to be a picnic either. So, your best bet is to prevent them in the first place. Read on to find out how.

Kidney stone facts and myths

  • Kidney stones are twice as common in men than women.
  • 11 percent of men and 6 percent of women in the United States will have a kidney stone at some time in their life.1
  • Summer is kidney stone season because people are more likely to sweat and become dehydrated, making it easier for mineral deposits to precipitate out.
  • The southeastern United States is considered the kidney stone belt, because of the hot, humid weather, which causes more sweating and likelihood of dehydration. 
  • Eating calcium-rich foods or taking a calcium supplement does not cause calcium-containing stones – that’s an old wives’ tale. It’s possible if you were to pop TUMS or Rolaids all day, you might be at some increased risk, but calcium supplementation at recommended amounts is not putting you at risk. Taking calcium in its citrate form is your best bet for urinary tract health (read on to find out why).*

Risk factors

In addition to hot weather and not drinking enough water to stay hydrated, there are several other risk factors associated with kidney stone prevalence.

  • Family history or personal history of kidney stones
  • Being overweight or having gained significant weight
  • High dietary intakes of sodium, animal protein, or sugar, which can increase loss of calcium in the urine; animal protein also increases risk of uric acid stones
  • Eating foods high in oxalates (more on this below)
  • Heavy use of alcohol
  • Gastrointestinal issues – bypass surgery, inflammatory bowel disease
  • Frequent urinary tract infections – increase the risk for struvite stones (made of magnesium ammonium phosphate)
  • Certain metabolic diseases, like hyperparathyroidism
  • Some medications, such as antacids, seizure medications, laxatives, or diuretics
  • Disruptions to the microbiome by antibiotic use because there are specific gut bacteria that metabolize oxalates so they’re not absorbed – one such bacteria is Oxalobacter formigenes, which is particularly susceptible to destruction by antibiotics.

How to decrease the risk

Hydration. Staying properly hydrated should be number one on your list for preventing kidney stones. This is especially important during the summertime, after heavy exercise, or when engaging in anything that increases fluid loss. To prevent repeat kidney stones, the Urology Care Foundation recommends drinking at least ten 10-ounce glasses of water daily. 

Check out these resources on Take 5 Daily with tips for staying hydrated.

Oxalate foods to avoid or eat on a limited basis.2 As mentioned above, the most common type of kidney stone is made of calcium oxalate. Oxalates can bind to calcium and form crystals in your urine. Therefore, it should come as no surprise that eating foods high in oxalic acid (oxalates) – like in the following list – might increase your kidney stone risk.

  • Certain green leafy vegetables: 900 mg in a half cup of red-stalked Swiss chard, 755 mg in a half cup of spinach, and 500 mg in a half cup of white-stalked Swiss chard
  • Rhubarb: 570 mg in a 3.5-ounce serving of rhubarb stalk (there is a much higher amount in the leaves – up to 1,900 mg per serving – although the leaves are rarely eaten)
  • Soybeans: 336 mg in a cup of soy milk or soy yogurt; 235 mg in a 3-ounce serving of firm tofu
  • Beets: 152 mg in one cup (found in both the root and the greens)
  • Almonds: 122 mg in a 1-ounce serving (about 22 nuts); Brazil nuts and pine nuts are also high in oxalates
  • Baked potato: 97 mg in a medium potato (mostly in the skin)
  • Navy beans: 76 mg in a half cup
  • Raspberries: 48 mg in one cup
  • Dates: 24 mg in one date!

Alternative foods to substitute.2 Intuitively you might think that foods with similar qualities would have similar oxalate levels, but that is not necessarily true. Also, cooking vegetables can decrease soluble oxalates (the ones most readily absorbed and likely to cause a problem). According to one study, boiling was more effective than steaming vegetables to remove oxalates. Baking (used in the case of a baked potato) did not remove any oxalates.3

  • Green leafy vegetables: 2 mg in a cup of kale and 1 mg in a cup of bok choy (substitute for spinach or Swiss chard)
  • Nuts (per ounce): 30 mg in cashews, 14 mg in pistachios; 12 mg in Macadamia nuts; 10 mg in pecans; 8 mg in walnuts; 0 oxalates in coconut (substitute for almonds, Brazil nuts, or pine nuts)
  • Seeds:   2 mg in one ounce of pumpkin or sunflower seeds; 2 mg in 2 tablespoons of ground flaxseeds
  • Beans: 15 mg in a half cup of kidney beans (that one should be easy to remember; substitute for navy beans)
  • Berries:  4 mg in a cup of blueberries or blackberries (substitute for or mix in with raspberries)
  • Potato: 28 mg in a sweet potato (compared to 97 mg in a white potato)
  • Figs: 9 mg in one fig (substitute for dates)
  • And don’t forget your broccoli, which has only 2 mg in a cup.

For a more extensive list of food oxalate content, consult this chart, provided by the UC Irvine Kidney Stone Center.

Tea – a controversial issue

The issue of tea consumption and its relationship to kidney stones is controversial. Although true tea from Camellia sinensis has varying levels of oxalates and is sometimes fingered as a culprit in kidney stone formation, several studies have found tea drinkers have a lower kidney stone risk. One study found a 16-percent decreased risk of kidney stones in individuals who drank 1-2 cups of tea (type unspecified) daily compared to those who drank less than one cup per week.4  In that same study, beverages with added sugars or artificial sweeteners increased the risk, while coffee (caffeinated and decaffeinated), red wine, orange juice, and beer decreased the risk.

If you are looking for tea with the lowest oxalate content, then this is how they stack up in the order of highest to lowest amount: Black tea, oolong, pu-erh, green tea, white tea, and purple tea. Even black tea has only about 5 mg of oxalates per cup. But it’s the habitual nature of tea drinking that might be a problem for some individuals. A scenario that could increase risk (and I speak from experience here) is drinking large amounts of iced tea during hot weather.

If you are at risk for kidney stone formation, particularly calcium oxalate stones, then your best bet might be to drink green tea. A study on stone-formers with high levels of calcium in their urine found that green tea did not increase the risk for men or women and even seemed to prevent stone formation in women.5 But if you’re a black tea lover, don’t despair. One study found that adding milk to black tea reduced the absorption of soluble oxalates to a negligible amount.6

Supplements can support dietary recommendations

You might be wondering if there are any vitamins or minerals that could be of benefit for urinary tract health. There are in fact a handful of nutrients that can help keep crystals from forming in the urine.

Magnesium can provide benefit in several ways. It inhibits absorption of oxalates from the gut and also helps prevent formation of calcium oxalate crystals in the urine.* But in order to do the latter, magnesium must be absorbed, so the form of the mineral matters. Studies have shown benefit from magnesium citrate, but not from magnesium oxide.7 This is partly because magnesium oxide is poorly absorbed and partly because the “citrate” in magnesium citrate also provides benefit. 

Citric acid (citrate) binds to calcium oxalate stones in the urine and keeps them from growing.* So, while any form of well-absorbed magnesium can provide benefit, magnesium citrate can provide a 1-2 punch.* And citrate bound to other minerals like calcium can provide benefit, too.*

Potassium in the form of citrate has a similar effect to magnesium citrate. Potassium decreases urinary excretion of calcium and the citrate portion can bind to the stone and keep it from growing.* Potassium also alkalinizes the urine.* Making the urine less acidic could provide benefit for individuals who tend to get uric acid stones,* since that type of stone flourishes in acidic urine.

Vitamin B6 can decrease oxalate production, lowering its amount in the urine.* One study found women in the highest vitamin B6 dietary-intake group were 34-percent less likely to form a kidney stone than women in the group with the lowest dietary intake.*8 This same study found vitamin C had no effect on risk.

In addition to magnesium’s benefit on the content of the urine, it is essential for helping to keep calcium in the bones and out of the soft tissues like the kidney. Vitamin D increases calcium absorption and in a manner similar to magnesium, vitamin K helps direct calcium to the bones and away from soft tissues.* That is why Thorne often recommends pairing vitamin K with vitamin D, as well as magnesium with calcium.

This is a lot of information to unpack, but if you remember nothing else – remember to drink plenty of water!

References

  1. National Institute of Diabetes and Digestive and Kidney Diseases. Definition & Facts for Kidney Stones. [Accessed July 14, 2023]
  2. WebMD. https://www.webmd.com/diet/foods-high-in-oxalates [Accessed July 14, 2023]
  3. Chai W, Liebman M. Effect of different cooking methods on vegetable oxalate content. J Agric Food Chem 2005;53(8):3027-30. doi: 10.1021/jf048128d. 
  4. Ferraro PM, Taylor EN, Gambaro G, Curhan GC. Soda and other beverages and the risk of kidney stones. Clin J Am Soc Nephrol 2013;8(8):1389-1395. doi: 10.2215/CJN.11661112. 
  5. Rode J, Bazin D, Dessombz A, et al. Daily green tea infusions in hypercalciuric renal stone patients: no evidence for increased stone risk factors or oxalate-dependent stones. Nutrients 2019;11(2):256. doi: 10.3390/nu11020256.
  6. Savage GP, Charrier MJ, Vanhanen L. Bioavailability of soluble oxalate from tea and the effect of consuming milk with the tea. Eur J Clin Nutr 2003;57(3):415-9. doi: 10.1038/sj.ejcn.1601572.
  7. Massey L. Magnesium therapy for nephrolithiasis. Magnes Res 2005;18(2):123-126. 
  8. Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Intake of vitamins B6 and C and the risk of kidney stones in women. J Am Soc Nephrol 1999;10(4):840-5. doi: 10.1681/ASN.V104840.