Canned tuna is a convenient and widely consumed source of protein, but concerns sometimes arise regarding its potential to contain high levels of histamine. Histamine is a naturally occurring chemical that plays several roles in the human body, yet excessive amounts can lead to adverse reactions in certain individuals. The presence of histamine in any fish product is not inherent to the fresh catch but is instead a direct result of improper handling and storage in the supply chain. Understanding how this compound forms and how the body processes it clarifies the true risk associated with this popular pantry staple.
What Histamine Is and Why It Causes Reactions
Histamine is a chemical messenger essential for normal bodily functions, acting as a neurotransmitter and playing a significant role in the immune system. Mast cells release this compound during allergic reactions to cause inflammation. It also assists in regulating stomach acid production for digestion.
Problems arise when the body’s capacity to metabolize histamine is overwhelmed, a condition sometimes referred to as histamine intolerance. The primary enzyme responsible for breaking down histamine ingested through food is Diamine Oxidase (DAO), which operates mainly in the digestive tract. When DAO activity is low, due to genetic factors, certain medications, or compromised gut health, dietary histamine can accumulate.
This buildup can then bind to receptors throughout the body, leading to a wide range of systemic symptoms. Low DAO activity means that even a typical amount of histamine from food can exceed the body’s detoxification limit.
How Histamine Forms in Tuna
Histamine is not naturally present at high levels in freshly caught tuna; it forms after the fish dies through bacterial decomposition. Tuna and other scombroid fish naturally contain high amounts of the amino acid histidine. Certain bacteria, particularly those found on the skin and gills (like Morganella morganii), convert this histidine into histamine using an enzyme called histidine decarboxylase.
The rate of this conversion is heavily dependent on temperature, making temperature abuse the largest factor in histamine accumulation. If the tuna is not rapidly and consistently chilled immediately after being caught, the bacteria multiply quickly, and histamine production accelerates. Allowing tuna to remain at temperatures above 40°F (4.4°C) for even a few hours can lead to potentially toxic levels of histamine.
The canning process involves high-heat sterilization, which destroys the bacteria responsible for producing histamine. However, this heat does not eliminate the histamine already formed because histamine is a heat-stable compound. Canned tuna carries a risk only if the raw fish was mishandled before reaching the cannery. The industry manages this risk through strict time-temperature controls, including rapid freezing at sea.
Identifying Symptoms of Scombroid Poisoning
Acute illness resulting from ingesting fish with excessively high histamine levels is called scombroid poisoning. This reaction is a form of chemical intoxication, not a true allergy, although the symptoms closely resemble an allergic response. Symptoms typically manifest quickly, often within 10 to 60 minutes after consuming the contaminated fish.
Common initial symptoms include flushing or reddening of the face and upper body, a tingling or burning sensation around the mouth, and a headache. These can rapidly progress to nausea, vomiting, dizziness, and heart palpitations. In more severe cases, individuals may experience respiratory distress or blurred vision.
Most reactions are mild and resolve on their own within a few hours, though they may last up to two days. The reaction is highly dose-dependent, meaning the severity relates directly to the amount of histamine consumed.
Reducing the Risk in Canned Tuna
Since histamine is heat-stable and cannot be eliminated by cooking or canning, minimizing risk begins with selecting products from reputable brands that emphasize rapid processing and cold chain integrity. Consumers should look for signs of quality control, such as certifications or statements regarding immediate freezing-at-sea practices. Avoiding cans that are visibly damaged, dented, or bulging is also a safeguard, as a compromised seal can introduce bacteria.
Once the can of tuna is opened, the focus shifts to preventing post-processing histamine accumulation. Opened tuna should be treated as highly perishable food and kept refrigerated at or below 40°F (4.4°C). If the opened tuna is left at room temperature, any bacteria present can begin to multiply and produce histamine rapidly.
Leftover canned tuna should be consumed within one to two days of opening, even when refrigerated, to prevent potential histamine buildup. Using smaller cans for single servings can help eliminate the need for lengthy storage. Water-packed tuna may sometimes offer better indicators of freshness than oil-packed varieties, as the oil can mask signs of spoilage.