Is the Nitrate in Leftover Vegetables Harmful?

Cooked broccoli, carrots, and cauliflower in a bowl

Philippe Desnerck / Getty Images

For most of us, eating leftover vegetables will not cause problems as long as they’re not spoiled and are reheated properly (neither of which has to do with nitrates; these are just good food safety practices). There are two times when you will need to be cautious about nitrates.

One of those times is during the first four months of life—but it’s not likely that babies that young are eating leftover vegetables or anything else. They should be consuming only breast milk or infant formula. Babies can be exposed to excessive amounts of nitrates if their formula is made from well water.

The second time to be cautious about nitrates is during the last 8 to 10 weeks of pregnancy. But again, this refers to drinking water contaminated with really high levels of nitrates—not the amount typically found in fresh or reheated vegetables.

Harmful Nitrates

Nitrates are naturally found in soil and water. They’re formed when microorganisms convert organic wastes into ammonia, which reacts with oxygen to form nitrate and nitrite.

Well Water Contamination

Nitrates are found in fertilizer, some rodenticides, and human and animal waste. Rural well water can become contaminated from nearby seepage from the fertilized soil, municipal, or industrial wastewater, landfills, animal feedlots, or septic systems.

The federal standard for nitrate levels in drinking water is 10 milligrams per liter. If you have a well with more nitrate than that, you may have to go through extreme measures to use that water.

Food Preservation

Sodium nitrate is a food preservative that’s often used to cure meat. You’ll find it in processed meats like bacon, ham, and sausage. Large observational research studies show that people who eat larger amounts of these meats tend to have higher risks of diseases like heart disease and some forms of cancer.

The natural response is to point the finger at the nitrates in the processed meat. But processed meats are also high in calories, saturated fat, and sodium.

Plus, people who eat lots of processed meats also tend to eat fewer fruits and vegetables, get less fiber, and consume more calories, smoke more, drink more, and exercise less. These are all risk factors for poor health outcomes.

If nitrates are accompanied by vitamin C (ascorbate or ascorbic acid), you don’t have to worry about them forming unhealthy, harmful substances in your body. When you see nitrates on your ingredient list, you’ll likely also see vitamin C.

Helpful Nitrates

Vegetables that grow in the soil are going to contain some nitrate. In fact, about 85% of your daily nitrate intake—about 20 to 25 milligrams per day—comes from vegetables. Cauliflower, spinach, collard greens, broccoli, and root vegetables contain more nitrates than other vegetables.

And vegetables are good for you. If anyone tells you that vegetables are bad for you because of the nitrates or any other reason, you should run from them. Very fast.

Some scientists posit that nitrates may even be part of the reason vegetables are good for you. It may be that nitrates are good for your blood vessels, help reduce blood pressure, and keep the platelets in your blood from clotting too much or in the wrong places.

Reheating Vegetables

It's true that if you re-boil water, you’ll concentrate the amount of nitrates as the water evaporates. Maybe people fear that reheating vegetables does the same thing.

But to concentrate nitrates, you'd have to reheat your vegetables to the point where they’re dried up, shriveled, and concentrated into a nasty lump. At that point, you're unlikely to eat them!

A Word From Verywell

Eat your vegetables. Save the leftovers. Heat them and eat them to avoid food waste and to get your daily veggie quota. There's no need to worry about the nitrates in vegetables, no matter how they are prepared.

7 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Agency for Toxic Substances and Disease Registry. ATSDR case studies in environmental medicine nitrate/nitrite toxicity.

  2. Agency for Toxic Substances and Disease Registry. What are U.S. standards and regulations for nitrates and nitrites exposure?.

  3. Alshahrani SM, Fraser GE, Sabaté J, et al. Red and processed meat and mortality in a low meat intake population. Nutrients. 2019;11(3):622. doi:10.3390/nu11030622

  4. Zhang Y, Zhao G, Cheng P, et al. Nitrite accumulation during storage of tomato fruit as prevented by hydrogen gas. Int J Food Prop. 2019;22(1):1425-1438. doi:10.1080/10942912.2019.1651737

  5. Jackson JK, Patterson AJ, Macdonald-Wicks LK, et al. Dietary Nitrate and Diet Quality: An Examination of Changing Dietary Intakes within a Representative Sample of Australian Women. Nutrients. 2018;10(8):1005. doi:10.3390/nu10081005

  6. Agency for Toxic Substances and Disease Registry. Nitrates/nitrites poisoning patient education care instruction sheet.

  7. Machha A, Schechter AN. Inorganic nitrate: A major player in the cardiovascular health benefits of vegetables?. Nutr Rev. 2012;70(6):367-372. doi:10.1111/j.1753-4887.2012.00477.x

Additional Reading

By Shereen Lehman, MS
Shereen Lehman, MS, is a former writer for Verywell Fit and Reuters Health. She's a healthcare journalist who writes about healthy eating and offers evidence-based advice for regular people.