Kidney stones are an all-too-common comorbidity of type 2 diabetes. Fortunately, there is a lot diabetics and others can do to keep them in check.
Here is a reprint on an article I wrote in 2003.
Sometimes writers who are kind enough to address us in English even though it is not their first language don't quite hit their mark. An ad promoting a part of Tuscany as "The Delicious Italy," for instance, read, "Fine restaurants of Gubbio use all the fruits of the forest to make the very best of the pasta around. Mushrooms as well as rabbit and other wild game make sure fine red wines and kidney stones are guaranteed."
And this "guarantee" of kidney stones, known in the medical literature as renal calculi, must have made the research of four Italian scientists named Cirillo, Laurenzi, Panarreli, and Stamler easier. These scientists at the University of Naples studied the diet of residents of Gubbio in relationship to risk of renal stones. They obtained urine samples from more than 3,000 residents of Gubbio, of whom 127 had a history of the condition. Urine samples were used to determine their sodium and potassium intakes.
Their findings? The Gubbioni who had the lowest levels of potassium and the highest levels of sodium in their urine had the highest rates ofstones. Residents in the highest quartile of sodium consumption were 3 to 9 times more likely to develop stones.
The relationship of dietary salt to kidney stones has also been studied in Texas. Scientists at Southwestern Medical School in Dallas found that a high salt diet increased the amount of sodium and calcium excreted into the urine, as well as making the urine much more alkaline. A high salt diet also decreased the excretion of citrate, leaving more citrate in the kidneys to form calcium citrate stones. Clearly, lowering salt is a good idea if you are prone to having this kidney problem.
What you can do about stones? The scientists at Southwestern Medical School studied diets that were unquestionably high in sodium-at least 5 grams a day over the amount of salt already in foods, equivalent to 1-2 tablespoons of added salt at every meal. Demonstrating reduced calcium excretion-less of the raw materials for making stones-required lowering the daily amount of sodium in the diet to 1,000 mg. I recommend that you consume no more than 1,500 mg a day, and that you consume nine servings of fruits and vegetables every day to obtain approximately 3,500 mg of potassium.
What you can expect. I can't guarantee that sodium restriction will protect you from future attacks. The evidence only suggests that attacks will be less frequent if you follow a low-sodium, high-potassium diet.
What foods may help prevent the formation of kidney stones? In the United States, women are more likely to develop stones if they have a history of high blood pressure, if they have not used calcium supplements, and if their diets are low in magnesium-rich foods such as beans, broccoli, nuts and seeds (especially peanuts), leafy greens, and soy.
Women whose sisters develop stones are more likely to develop kidney stones themselves if their urine is high in calcium and unusually alkaline. (Making urine more alkaline by using cranberry extract tablets is a risk factor for kidney stones in women.) Men are more likely to develop stones if they have uncontrolled high blood pressure. Men whose brothers have stones are more likely to develop stones as they grow older and if their urine potassium levels are low or their urine calcium levels are high. Children on extremely high-fat diets are at risk of stones unless they consume adequate amounts of fluid.
Vitamin B6 may reduce the risk of kidney calcifications in women. A study of 85,557 women by the Harvard School of Public Health found that women consuming the greatest amount of the vitamin had risk reduced by approximately one-third. A study of 45,251 men by the Harvard School of Public Health found that consuming vitamin B6 reduced risk of kidney stones by approximately 10 percent. Since vitamin B12 is possibly linked to increased risk of stones, it is best to use a B6 supplement rather than a complete B-vitamin.
Or better yet, eat foods that are rich in vitamin B6. These include avocados, bananas, barley, bok choy, brown rice, chicken, chickpeas, fresh pork, mangoes, rice, salmon, and turkey.
The simplest yet most essential task in preventing stones in the kidneys is drinking enough water. Adequate hydration helps ensure that the volume of urine will be enough to dissolve the minerals that can cause stones. Some other beverages are helpful. Survey data collected by the Harvard School of Public Health shows that consuming 1 cup (240 ml) of coffee daily (regular or decaffeinated) reduces the risk of calcificatons by 10 percent, the same amount of tea, 14 percent, beer, 21 percent, and wine, 39 percent. (The data do not show that drinking large quantities of any of these beverages eliminates the risk of stones). Juices tend to be harmful.
The same survey also found that drinking a cup of apple juice daily increased the risk developing kidney stones possibly by 75 percent and drinking a cup of grapefruit juice daily increased the risk of stones by as much as 85 percent. While using cranberry juice tablets increases the risk of stones in women, no study has found that cranberry juice itself increases the risk of kidney stones.
Since most stones are made of calcium, it would seem logical that reducing dietary calcium would reduce the risk of stones. Reducing consumption of calcium-rich foods does reduce the amount of calcium in the urine, but it increases the amount of the other component of most kidney stones, oxalate. Rather than reducing the risk of stones, a low-calcium diet nearly doubles the risk of recurrent kidney stones, at least in men. Even taking calcium supplements, in the form of calcium citrate, does not increase the risk of renal calculi.
Similarly, since most renal calculi contain oxalate, it would seem logical to limit consumption of foods that are high in oxalic acid, such as almonds, beet greens, bran, chocolate, rhubarb, spinach, strawberries, and tea. No study, however, has found that restricting consumption of these foods increases the risk of kidney involvement and some studies have found that consumption of leafy greens, peanuts, and tea actually reduce the risk of stones. The vitamin K in green leafy vegetables may be one reason vegetarians have a lower incidence of kidney stones.
Consumption of animal protein is likewise an accepted risk factor for kidney stone disease, but clinical testing has found that only about one-third of people who get kidney stone complications are adversely affected by a high-protein diet. It seems sensible to avoid excessive consumption of meat, but severe protein restriction probably will not help.