Kidney Stones, Low Urinary Citrate, and Lemonade Stands

Today this episode is again focusing on kidney stone prevention. Today’s focus is on a mineral called citrate. C-i-t-r-a-t-e.

Citrate is a naturally occurring substance. It is a salt or ester of citric acid. Citric acid is found in relatively high amounts in citrus foods and juices, lemon and lime juice have some of the highest amounts of citric acid, but other citrus juices such as orange juice do as well. Citric acid is not to be confused with Vitamin C which is ascorbic acid.

Urinary citrate is an inhibitor of kidney stone formation due in part to binding of calcium in urine. Citrate in the urine inhibits crystal formation, growth and aggregation. If you don’t have enough citrate in your urine, something we call hypocitraturia, you may be at risk for forming kidney stones. 

Here is the point of this episode. If you want to increase your urinary citrate and decrease your kidney stone risk you can drink, you guessed it, lemonade. Who knew?

Here is how kidneys work. Your two kidneys are each made up of about one million nephron units. A nephron is a complete and complex structure that begins its function by filtering blood at the glomerulus, a tuft of capillaries nestled in a tiny filtering cup. The filtrate is a clear solution of water and small molecules. That filtrate enters a long and loopy set of tubules that reabsorb a vast fraction of the water and salts and minerals back into the blood leaving behind only the stuff destined for export out of the body in the form of urine into its collecting ducts. The collecting ducts drain into the renal pelvis and ureter as small tributaries do to form a river. The renal pelvis and ureters drain into the bladder.

The cells that line the tubules of the nephron regulate what fractions of innumerable individual salts and small molecules are taken back or let go into the urine.

For the many nutrients and byproducts of our metabolism the kidneys offer the only way out of the body. Minerals and electrolyte salts flow through our bloodstream from the food we eat. For each molecule passing through the kidney, the kidney determines what get excreted as urine and what is left behind.

Here, then, is how kidney stones form. Your urine is very concentrated because of the concentration of minerals by the kidneys at the level of the glomerulus and the tubules. The urine becomes supersaturated with minerals and salts. Supersaturated fluid can form crystals because the minerals and salts fall out of solution.

An example of supersaturation is when you boil sugar water to make rock candy. You then place the concentrated liquid in a glass, drop a string or stick in it, and crystals form on the string or stick to make rock candy.  

Supersaturation with respect to the most common type of stones, calcium oxalate and calcium phosphate stones depends upon urine concentrations of calcium, oxalate, phosphate, citrate, and urine pH.

Drinking adequate fluids (at least ten 8-ounce glasses per day) is the most powerful way to decrease your risk of developing stones by diluting the urine to make it less supersaturated. 

But, as I said before urinary citrate, the amount of the mineral citrate in your urine is a major inhibitor of kidney stone formation. Citrate in the urine inhibits crystal formation, growth and aggregation. Urine citrate binds urine calcium in a soluble citrate complex, which reduces calcium salt supersaturations.

If you are a kidney stone former your doctor can measure your level of urinary citrate excretion along with other minerals in a 24-hour urine collection. A 24-hour urine collection is every drop of urine you produce over exactly 24-hours collected in a large jug by you at home, and then brought to a laboratory for analysis.

Low urine citrate levels are considered a risk for kidney stone formation. Hypocitraturia. Hypo, meaning low. Citraturia. Low urinary citrate levels.

Low urinary citrate promotes kidney stone formation and growth. Conditions that lowers renal tubular pH or intracellular pH may decrease citrate and must be corrected (eg, metabolic acidosis, increased acid ingestion, hypokalemia, or hypomagnesemia). But for most stone formers altering diet or using a medication called potassium citrate is how we increase the amount of citrate in the urine.

Pharmacological doses of citric acid, prescribed as potassium citrate, are effective in the treatment of stones. But potassium citrate tablets are big horse pills, and they can be expensive. And some patients require several tablets daily.

Which bring us back to citric acid as a way to increase urinary citrate. Citric acid is an organic acid and a natural component of many fruits and fruit juices. Of these fruits, lemons and limes have the most citric acid.

Citrate inhibits stone formation and breaks up small stones that are beginning to form. it prevents small stones from becoming “problem stones” by coating them and preventing other material from attaching and building onto the stones. Citric acid is protective; the more citric acid in your urine, the more protected you are against forming new kidney stones.

A half-cup (4 ounces) of pure lemon juice per day or 32 ounces of prepared lemonade per day provide about the same amount of citric acid as does pharmacological therapy with the big expensive horse pills.

Yes, that is a lot of lemons and lemonade.

But you can use commercially available lemonade products and mixes. Use low-calorie lemonades and lemonade mixes that are high in citric acid but have less sugar. Of the commercially-available lemonade products, those that are ready-to-consume generally have more citric acid than those that come as a powder.

To make homemade lemonade, squeeze a 1⁄2 cup (4 ounces) of fresh lemon juice into a pitcher of cold water; bottled lemon juice may also be used. Add sugar or sugar substitute, if desired. Voila, lemonade.

Here are some other suggestions to add lemons or limes to your diet. You can freeze some lemon or lime juice into ice cubes. Use these cubes for sprucing up plain tap water and other beverages. You can Squeeze fresh lemon or lime juice directly into your soda, fruit juice, tea, or water. You can make lemon or lime spritzers. Lastly you can use fresh lemon on lettuce or spinach salads, fruit salads, or on fish and in marinades for any type of meat.