Nitrites are chemical compounds that, while useful in food preservation, can pose health risks at elevated concentrations. They are closely related to nitrates, which can transform into nitrites in the environment or within the human body through bacterial action. The primary health concern stems from nitrite’s ability to interfere with the body’s oxygen transport system.
Common Sources of Nitrite
Exposure to nitrites can occur through several channels, with food and water being the most significant. Cured and processed meats like bacon, hot dogs, and deli meats contain nitrites, added to preserve them, prevent bacterial growth, and maintain color and flavor. The U.S. Food and Drug Administration (FDA) and the Department of Agriculture (USDA) regulate the levels of these compounds in meat production.
Another source of exposure is drinking water, particularly from private wells in agricultural areas. Fertilizers used in farming contain nitrogen, which can seep into the ground and contaminate water sources as nitrates. When this nitrate-contaminated water is ingested, bacteria in the body can convert it into nitrite. This is a particular concern for infants when contaminated well water is used to prepare formula.
The human body also produces small amounts of nitrite. Bacteria in saliva and the digestive tract can convert nitrates from our diet into nitrites. Vegetables like spinach, beets, and carrots can be high in nitrates, though for most people, the amount converted in the body is not harmful. This internal production is a normal physiological process.
How Nitrite Affects the Body
Nitrite toxicity is directly linked to its effect on hemoglobin, the protein within red blood cells that transports oxygen from the lungs to the rest of the body. Hemoglobin contains iron in the ferrous (Fe2+) state, which allows it to bind to oxygen molecules. This process is fundamental for cellular respiration.
When nitrite enters the bloodstream, it oxidizes the iron in hemoglobin, changing it from the functional ferrous (Fe2+) state to the non-functional ferric (Fe3+) state. This altered molecule is called methemoglobin. The issue with methemoglobin is its inability to bind with and transport oxygen, reducing the blood’s oxygen-carrying capacity.
The increase of methemoglobin in the blood diminishes the ability to deliver oxygen to tissues. This condition is known as methemoglobinemia. The resulting oxygen deprivation, or hypoxia, causes the toxic effects of nitrite poisoning. The severity is directly related to the percentage of hemoglobin converted to methemoglobin.
Signs of Nitrite Poisoning
The signs of nitrite poisoning result from the body’s tissues being starved of oxygen. Initial symptoms can be subtle and include headaches, dizziness, fatigue, and shortness of breath. As the level of methemoglobin rises, more pronounced symptoms appear, such as a rapid heartbeat, confusion, and nausea.
A distinct sign of moderate to severe nitrite poisoning is cyanosis, a visible bluish or grayish discoloration of the skin, lips, and nail beds. This blue tint occurs because blood with non-oxygen-carrying methemoglobin is darker and appears blue through the skin. In severe cases, the lack of oxygen can lead to seizures, loss of consciousness, and death if not treated promptly.
Infants are susceptible to the effects of nitrites, a condition called “blue baby syndrome.” This vulnerability is due to several factors, including their gut bacteria and the presence of fetal hemoglobin, which is more easily oxidized to methemoglobin. Infants also have lower levels of the enzyme that converts methemoglobin back into functional hemoglobin, making it harder for their bodies to counteract the effects.
Managing Nitrite Exposure and Toxicity
Preventing nitrite toxicity involves limiting exposure from key sources. For those using private well water, it is important to have it tested for nitrates and nitrites by a certified laboratory. If levels are high, use a water treatment system for nitrate removal, as boiling water will not remove nitrates and can increase their concentration. Moderating the consumption of cured and processed meats also reduces dietary exposure.
Special care should be taken for infants. Avoid using untested well water for mixing infant formula. Home-prepared baby foods made from vegetables high in nitrates, like spinach or beets, should be avoided for infants younger than three months old. Breastfeeding is a protective measure, as nitrates do not significantly accumulate in breast milk.
Acute nitrite poisoning is a medical emergency that requires immediate professional care. The primary treatment for severe methemoglobinemia is the intravenous administration of methylene blue. This antidote helps an enzyme in the body to rapidly convert methemoglobin back into normal, oxygen-carrying hemoglobin, which restores the blood’s ability to transport oxygen.