Nitrates are naturally occurring chemicals found in plants and soils that can cause babies to develop a very rare and dangerous form of anemia. The amount of nitrates in a vegetable depends on the type of vegetable, the age of the plant, and environmental factors such as sunlight, moisture, soil composition, and fertilizer. Some foods (e.g., carrots, beets, green beans, squash, or spinach) tend to contain more nitrates than others.

Nitrate poisoning is usually associated with formula that’s been mixed with contaminated well water. For that reason, the American Academy of Pediatrics (AAP) recommends exclusive breastfeeding and regular water testing in areas where only well water is available. Parents should not prepare their baby’s formula or food with well water that is high in nitrates. Well water can be tested by a laboratory and should contain less than 10 ppm (parts per million) of nitrates. (Your local health department or health care provider should be able to provide guidance about how to get your water tested.)

The AAP also recommends not giving foods with nitrates to babies less than 3 months of age. Fortunately, at about 3 months of age, your baby’s stomach will begin to produce more hydrochloric acid, which destroys most of the nitrate-converting bacteria. Since most parents don’t start feeding solid foods to their babies until they’re around 6 months old, there is little need to worry about nitrates.

Still, to minimize your child’s exposure to nitrates: serve foods with nitrates right away (spinach, beets, cabbage, broccoli, and carrots all have nitrates, but leafy vegetables contain the highest amounts); select frozen vegetables instead of fresh for foods highest in nitrates (studies have shown that nitrate levels increase with storage time, unless the vegetables are frozen); and when using fresh vegetables to make your homemade baby food, prepare the food as soon as possible after purchase and freeze extra servings right away.