Citrates are salts or esters derived from citric acid, the same tart compound found naturally in lemons, limes, and other citrus fruits. They show up in a surprisingly wide range of places: inside your cells generating energy, in supplements and medications, in processed foods, and even in the tubes used to collect your blood at a lab. Understanding what citrates actually are helps make sense of why they appear on so many ingredient lists and prescriptions.
How Citrates Relate to Citric Acid
Citric acid is a small organic molecule with three acidic groups. When those groups lose their hydrogen atoms (which happens naturally in water or when combined with a mineral), the result is a citrate ion. Pair that ion with sodium and you get sodium citrate. Pair it with potassium and you get potassium citrate. Pair it with calcium and you get calcium citrate. Each version inherits certain properties from citric acid, like the ability to bind metals and influence acidity, but behaves differently depending on which mineral is attached.
Nearly all commercial citric acid, and by extension the citrates made from it, comes from microbial fermentation rather than squeezing fruit. A mold called Aspergillus niger is the primary workhorse: fed sugar from glucose syrup or beet molasses, it can produce up to 90 grams of citric acid per liter of liquid. About 80% of the world’s supply is made through submerged fermentation, where the mold grows in large tanks. The remaining 20% uses surface fermentation, an older technique where the mold grows on top of a shallow liquid bed.
Citrate’s Role in Energy Production
Inside your cells, citrate is the very first molecule formed in the citric acid cycle (also called the Krebs cycle), the central energy-producing pathway in virtually every cell of your body. The cycle begins when a two-carbon fragment from broken-down food combines with a four-carbon molecule called oxaloacetate. That reaction, which is essentially irreversible, produces citrate and kicks off a series of chemical transformations inside the mitochondria.
As the cycle turns, it strips high-energy electrons from carbon skeletons and loads them onto carrier molecules. Those carriers then feed into a separate process, the electron transport chain, which generates the vast majority of the ATP your body uses as fuel. This pathway handles the final breakdown products of carbohydrates, fats, and amino acids, making citrate a metabolic crossroads. When energy is abundant, citrate can also be diverted out of the cycle and used as a building block for fatty acid synthesis, essentially helping the body store excess fuel as fat.
Citrates in Food and Beverages
Sodium citrate, labeled as E331 on European packaging, is one of the most common food additives in the world. It serves several roles at once: it acts as a preservative, a flavor enhancer (it gives club soda both its sour and slightly salty taste), an antioxidant, and a pH buffer that keeps acidity levels stable during processing and storage.
One of its more popular uses in cooking is as an emulsifying salt. A small amount of sodium citrate can turn virtually any cheese into a perfectly smooth, melty sauce by preventing the proteins and fats from separating. It works by binding the calcium in the cheese that would otherwise cause clumping. The same calcium-binding ability makes it useful in molecular gastronomy techniques like spherification, where acidic liquids need their pH raised before they can form proper gel spheres.
Kidney Stone Prevention
Potassium citrate is widely prescribed for people who form kidney stones, particularly calcium-based stones. It works through two mechanisms: it makes urine less acidic (more alkaline), and it binds to calcium in the urine so that calcium can’t combine with oxalate or phosphate to form crystals.
Your kidneys naturally excrete citrate, and having enough of it in your urine is one of the body’s built-in defenses against stone formation. Healthy adults who don’t form stones excrete a median of about 640 mg of citrate per day. When levels drop below 320 mg per day, the condition is called hypocitraturia, and stone risk goes up significantly. Many kidney stone specialists recommend targeting at least 640 mg per day, or a concentration of 320 mg per liter of urine, as an optimal goal. For people who fall short, potassium citrate supplements help close the gap.
Citrate in Supplements
Beyond kidney stones, citrate forms are popular in mineral supplements because they tend to absorb well. Calcium citrate is a good example. A meta-analysis comparing calcium citrate to calcium carbonate (the other common form) found that calcium citrate was absorbed roughly 22% to 27% better, whether taken on an empty stomach or with food. That flexibility matters because calcium carbonate requires stomach acid for absorption and works best with meals, while calcium citrate works well regardless of timing. For people with low stomach acid or those taking acid-reducing medications, calcium citrate is generally the better choice.
Magnesium citrate is another widely used form. At supplement doses, it provides magnesium for general health. At higher doses, it acts as a saline laxative: the citrate pulls water into the intestines, softening stool and triggering a bowel movement typically within 30 minutes to 6 hours. This osmotic effect is why magnesium citrate is commonly used for bowel preparation before medical procedures.
Blood Collection and Laboratory Use
Sodium citrate plays a critical role in medical laboratories. When your blood is drawn into a light-blue-topped tube, that tube contains sodium citrate as an anticoagulant. It prevents clotting by binding to calcium ions in the blood, and calcium is essential for the clotting process to proceed. This technique has been used for over a century to stabilize blood and blood products. When lab technicians are ready to run coagulation tests, they add calcium back to the sample to restart the clotting process and measure how long it takes. This is the basis for common tests like prothrombin time (PT) and activated partial thromboplastin time (aPTT), which help assess bleeding disorders and monitor blood-thinning medications.
Common Side Effects of Citrate Supplements
Citrate-based supplements and medications are generally well tolerated, but they can cause digestive issues. The most frequent complaints are nausea, diarrhea, and stomach discomfort, particularly with magnesium citrate at laxative doses. Potassium citrate, because it raises potassium levels, requires more caution: people with kidney disease or those already taking medications that increase potassium need careful monitoring to avoid dangerously high blood levels.
For most people, the citrates encountered in food, supplements, and beverages are safe in normal amounts. They’re among the most thoroughly studied and widely used compounds in both the food and pharmaceutical industries, with a track record stretching back more than a century.