Dr. Cannell: Does vitamin D cause kidney stones?
Dr. Cannell replies:
It may, at least for people on modern American diets. The reason this has come up is because a recent study found the relative risk for people taking 400 units of vitamin D and 1,000 mg of calcium daily was 17% higher than in the placebo group. To my knowledge, this is the first study to find an increased risk of kidney stones with vitamin D supplementation. I’m not aware of any reports of increased incidence of kidney stones in any other vitamin D supplementation trial.
However, at least two studies have linked kidney stones to latitude, with an increasing incidence of stones at lower latitudes. One also directly linked stones to sunlight. A Saudi Arabian study found kidney stones were more common in the summer. Eleven of 45 lifeguards in Israel had kidney stones, which is twenty times the rate of the general population.
The largest study that looked at the risk of kidney stones with vitamin D came out of Harvard. They studied 45,616 men over 14 years for a total of 477,000 person-years of follow up. They found no increased risk of kidney stones with vitamin D intake but did not look at sun exposure or 25(OH)D levels. Of interest, they found three things in your diet that protect against kidney stones: high potassium (46% lower relative risk), high magnesium (29% lower relative risk), and high fluid intake (29% lower relative risk). For younger men, higher dietary calcium was associated with a reduced risk of kidney stones (31% lower relative risk).
It seems likely that physiological vitamin D intakes will result in a higher relative risk for kidney stones for people on modern American diets (low potassium, low magnesium, high refined carbohydrates, high sodas, and a high acid residue). You may lower your risk of kidney stones by remaining vitamin D deficient, but then you raise your risk of dying from many other diseases. The best thing to do to prevent kidney stones is be sure you drink adequate fluids, be sure you have adequate magnesium (see below) and potassium in your diet, and be sure you are not in a state of low-grade metabolic acidosis. The last is important, because foods that contain potassium (vegetables and fruit), also turn your body more basic.
Today, humans live in a state of low-grade metabolic acidosis, mainly caused from a modern diet of high animal protein, refined sugars, refined grain, and sodas—instead of an ancient diet of moderate protein and whole grain and lots of vegetables and fruit. The low-grade acidosis in modern humans leaches calcium from our bones, increases the amount of calcium in our urine, and causes kidney stones, hypertension, and even stroke. Also, vitamin D does not work as well in metabolically acidotic people. For those of you who just can’t eat five to nine servings of vegetables and fruit a day, 25 mEq of effervescent potassium bicarbonate every day in the form of a supplement is a good idea, as long as you are not taking a medication (usually for hypertension) that inhibits potassium excretion by the kidney.