DHA in Tuna: Amounts, Benefits, and Mercury Levels

Docosahexaenoic acid, or DHA, is a long-chain omega-3 fatty acid that contributes to human health and development. The human body is not efficient at producing DHA, making dietary intake the primary way to secure adequate levels. Tuna is one of the most widely consumed fish globally, and its accessibility in both fresh and canned forms makes it a common choice for obtaining this nutrient.

DHA Content in Different Tuna Varieties

The amount of DHA in tuna varies considerably across different species, a factor directly linked to the fish’s fat content. Fattier, cold-water fish generally store more omega-3s in their tissues. For instance, fresh Bluefin tuna, particularly the prized fatty belly cut known as otoro, contains the highest concentration of DHA, sometimes exceeding 1,200 milligrams per 3-ounce serving.

Albacore tuna, often sold as “white” canned tuna, provides approximately 1,000 mg of DHA per 3-ounce serving. In contrast, canned “light” tuna, made from smaller Skipjack or Yellowfin tuna, contains lower levels, usually offering between 200 and 300 mg of DHA. Fresh Yellowfin steaks fall between Albacore and light tuna in their DHA content.

These differences result from the distinct physiology and habitat of each species. Bluefin and Albacore are larger fish that live longer and accumulate more fat, which serves as a reservoir for DHA. Skipjack are smaller and have a shorter lifespan, resulting in leaner meat and consequently lower levels of omega-3s.

Health Significance of DHA from Tuna

DHA is a primary structural fat in the human brain and the retina of the eye. Within the brain, it accumulates in the cerebral cortex, the area responsible for higher-order thinking, memory, and language. Its incorporation into cell membranes influences signaling pathways and neurotransmitter function.

During pregnancy and early childhood, the demand for DHA is high, as it is fundamental for the proper development of the fetal brain, eyes, and immune system. DHA is transferred from the mother to the fetus across the placenta and later supplied to infants through breast milk. Adequate intake during these periods is associated with better neuronal and visual development in the child.

In adults, maintaining sufficient DHA levels supports cognitive processes and brain health, with research suggesting a connection to a reduction in age-related cognitive decline. DHA also exhibits anti-inflammatory properties. It serves as a precursor to molecules that help resolve inflammation, which may help manage conditions like rheumatoid arthritis and promote cardiovascular health by lowering blood triglyceride levels.

Balancing DHA Intake with Mercury Concerns

While tuna is a source of DHA, it also contains methylmercury, a compound that can be harmful to the developing nervous system. Mercury enters waterways from industrial sources and is converted by aquatic microbes into methylmercury. This compound builds up in fish through bioaccumulation, where the mercury concentration becomes more potent as larger predatory fish consume smaller ones.

The type of tuna consumed directly impacts mercury exposure. Larger, longer-living species like Bigeye and Albacore tuna have higher mercury levels than smaller species like Skipjack. Because of this, Albacore (“white”) tuna can have three times more mercury than canned light tuna.

The U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) have established joint recommendations, especially for pregnant or breastfeeding individuals and young children. For this population, the advice is to consume two to three 4-ounce servings of fish from the “Best Choices” list per week, which includes canned light tuna. The guidelines suggest limiting fish from the “Good Choices” list, like Albacore and Yellowfin tuna steaks, to one 4-ounce serving per week.

For the general population, tuna can be part of a healthy diet that includes a variety of fish. Opting for canned light tuna more often than Albacore is a practical strategy for regular consumers. This approach allows individuals to benefit from tuna’s protein and DHA content while adhering to established safety guidelines.