ROCHESTER, Minn. — Kidney stones can cause not only excruciating pain but also are associated with chronic kidney disease, osteoporosis and cardiovascular disease. If you’ve experienced a kidney stone once, you have a 30% chance of having another kidney stone within five years. Creapharma.com was able to interview co-author Dr. John Lieske.
Changes in diet are often prescribed to prevent recurrent symptomatic kidney stones. However, little research is available regarding dietary changes for those who have one incident of kidney stone formation versus those who have recurrent incidents.
Mayo Clinic researchers designed a prospective study to investigate the impact of dietary changes. Their findings show that enriching diets with foods high in calcium and potassium may prevent recurrent symptomatic kidney stones.
Dietary factors were based on a questionnaire administered to 411 patients who had experienced first-time symptomatic kidney stones and a control group of 384 people — all of whom were seen at Mayo Clinic in Rochester and Mayo Clinic in Florida between 2009 and 2018. The findings, which were published in Mayo Clinic Proceedings, show that lower dietary calcium and potassium, as well as lower intake of fluids, caffeine and phytate, are associated with higher odds of experiencing a first-time symptomatic kidney stone.
Of the patients who had first-time stone formation, 73 experienced recurrent stones within a median of 4.1 years of follow-up. Further analysis found that lower levels of dietary calcium and potassium predicted recurrence.
“These dietary findings may have particular importance because recommendations for preventing kidney stones have been based primarily on dietary factors associated with first-time rather than recurrent stone formation,” says Andrew Rule, M.D., a Mayo Clinic nephrologist and senior author of the study. “Patients may not be likely to adjust their diet to prevent an incidence of kidney stones, but they are more likely to do so if it can help prevent recurrence.”
Fluid intake of less than 3,400 milliliters per day, or about nine 12-ounce glasses, is associated with first-time stone formation, along with caffeine intake and phytate, the study finds. Daily fluid intake includes intake from foods such as fruits and vegetables.
Low fluid and caffeine intake can result in low urine volume and increased urine concentration, contributing to stone formation. Phytate is an antioxidant compound found in whole grains, nuts and other foods that can lead to increased calcium absorption and urinary calcium excretion.
“Changing your diet to prevent kidney stones can be very difficult,” says Dr. Rule. “Thus, knowing the dietary factors that are most important for preventing kidney stone recurrence can help patients and providers know what to prioritize.”
Low dietary calcium and potassium was a more important predictor than fluid intake of recurrent kidney stone formation, says Api Chewcharat, M.D., the article’s first author and a postdoctoral research fellow at Mayo Clinic at the time of the study. “This is not to say high fluid intake is not important. We just did not find benefits of increasing fluid intake among those patients with a history of kidney stone formation.”
The study concludes that diets with daily intake of 1,200 milligrams of calcium may help prevent first-time and recurrent kidney stones. That daily intake is in line with the Department of Agriculture’s daily recommended nutrition.
While higher potassium intake also is recommended, the USDA does not make a recommendation for daily potassium intake. The study also doesn’t recommend an intake level.
Dr. Chewcharat says the takeaway is that patients should add more fruits and vegetables that are high in calcium and potassium to their diets. Fruits that are high in potassium include bananas, oranges, grapefruits, cantaloupes, honeydew melons and apricots. Vegetables include potatoes, mushrooms, peas, cucumbers and zucchini.
Interview with Dr. John Lieske
CREAPHARMA.COM – What are the main findings of your study? What message would you like to send?
Dr. John Lieske – We have studied first-time kidney stone formers at Mayo Clinic Rochester and Florida for over 10 years. We also have recruited matched controls without stones. As part of the study, all participants completed a food frequency questionnaire which gives us information about their diet average over the 3 months prior. In this study we found that dietary fluid intake, calcium intake, potassium, among other things were different between the stone formers and controls at baseline. We also were able to identify the cut off for fluid intake (3400 ml) and calcium intake (1200 mg) where the benefits plateaued. In addition we have followed the stone formers over time for recurrent stones. We identified that lower calcium diet was significantly associated with the risk of recurrence. This is one of the 1st studies that really demonstrates this effect of low calcium intake increasing the risk of recurrent kidney stones.
One of the advantages of our study is that these were first-time stone formers representative of the general community. Often times kidney stone studies are done in larger clinics with referral of harder cases which may not be representative of the general population.
CREAPHARMA.COM – You mention in your press release that kidney stones are associated with osteoporosis and cardiovascular disease, do we know why this association?
Dr. John Lieske – Excretion of high amounts of calcium in the urine is a common risk factor for calcium kidney stones and this is often familial or genetic in nature. Although the mechanisms are being worked out, likely many of the underlying genetic causes are related to calcium metabolism and can also increase your risk of bone loss over time. As studies are completed over the coming years I think we will understand more about this association on a relatively specific basis.
Although the association between cardiovascular events and kidney stones has been made in many studies, the exact reasons are not entirely clear. Certainly part of it has to do with common underlying risk factors since obesity, metabolic syndrome and diabetes. All known risk factors for both kidney stones and cardiovascular events.
CREAPHARMA.COM – You mention calcium and potassium intake through the diet, can taking food supplements also help? Have you tested this?
Dr. John Lieske – The question of calcium supplements is particularly interesting.. Studies suggest that while dietary calcium can reduce kidney stone risk, calcium pills supplements probably increase it to some extent. Thus, we would prefer our stone patients get their calcium through natural sources including dairy. The studies that look at potassium intake and kidney stone risk, like our current one, are also looking at dietary sources as opposed to supplements. Whether not supplemental potassium in pill form would have the same benefit is not known. A lot of the foods that are rich in potassium are fruits and vegetables at also have plenty of citrate which is also protecting in stones. Thus, it may be important how you get your potassium as well.
CREAPHARMA.COM – It is known that consuming too much potassium can be problematic for people with kidney problems. Is there less risk of having an excess of potassium in the diet (compared to dietary supplements for example)?
Dr. John Lieske – In general, individuals can get rid of plenty of potassium by their kidneys unless kidney function is markedly reduced. The range of potassium intake we are talking about here would be more or less along the normal spectrum that people get in their diets. We would not expect this to be an issue unless the patient had stage IV or 5 chronic kidney disease. In general, such individuals would be known and should be followed by a kidney specialist.
CREAPHARMA.COM – In the press release you mention foods rich in potassium, do you also recommend or suggest some foods rich in calcium?
Dr. John Lieske – In general, foods rich in calcium that we think would be helpful for stone prevention would include dairy products such as low-fat milk, yogurt, and cheese.
CREAPHARMA.COM – In addition to eating foods rich in calcium and potassium, what other tips do you have for reducing the risk of kidney stones?
Dr. John Lieske – One other general strategy which is helpful for reducing the risk of kidney stones is drinking plenty of fluid. The amount of calcium and oxalate and other molecules we excrete in our urine is almost entirely independent of the urine volume. Thus the calcium and oxalate that make common calcium oxalate kidney stones can be very concentrated if you are drinking very little, or very dilute if you drinking plenty of fluid. There is currently an ongoing NIH study to look at strategies to increase fluid intake and to determine if that translates into reduced kidney stone risk.
The other general dietary measures that I think could be useful in most calcium stone formers would be reducing their dietary sodium intake. It turns out that the kidney will eliminate more calcium, on average, if you are on a higher sodium diet. We did not see clear relationships between the sodium intake by the food frequency questionnaire and kidney stone risk in our study, but sodium is very difficult to capture on a food frequency questionnaire since it is in so many foods.
August 2, 2022. Interview made by email in early August by Xavier Gruffat (pharmacist) with Dr. John Lieske.
