What are the potential adverse effects of a diet high in tuna, particularly in relation to mercury (Hg) toxicity and its impact on human health?

From the Guidelines

A diet high in tuna can pose health risks primarily due to mercury contamination, and it is recommended to limit albacore (white) tuna to no more than 6 ounces per week for adults and even less for children and pregnant women, who should consume no more than 4 ounces weekly, as suggested by the FDA 1. When considering the risks associated with a diet high in tuna, it's essential to weigh the benefits of omega-3 fatty acids against the potential harm caused by mercury contamination.

• Large predatory fish like tuna accumulate methylmercury in their tissues, which can cause neurological damage in humans when consumed in excessive amounts.
• The FDA recommends limiting albacore (white) tuna to no more than 6 ounces per week for adults and even less for children and pregnant women, who should consume no more than 4 ounces weekly 1.
• Canned light tuna generally contains less mercury and can be eaten more frequently (up to 12 ounces weekly) 1. Some studies suggest that the benefits of fish consumption, including tuna, may outweigh the risks for certain populations, such as middle-aged and older men and postmenopausal women 1. However, it's crucial to note that excessive tuna consumption may lead to an imbalanced diet lacking in other essential nutrients, and some tuna products contain high sodium levels, which can contribute to high blood pressure when consumed regularly. To maintain a healthy diet while enjoying tuna, it's recommended to:
• Vary seafood choices to include low-mercury options like salmon, sardines, and trout.
• Balance fish consumption with plenty of fruits, vegetables, and whole grains. According to a more recent study, the benefits of seafood consumption, including tuna, on cardiovascular health are well-established, and the American Heart Association recommends consuming at least 1 to 2 fish servings (3.5 oz per serving), preferably oily fish, per week 1. Additionally, another study found that methylmercury consumed from fish has no detectable influence on incident cardiovascular events, hypertension, or diabetes, but women who are or may become pregnant or nursing should follow FDA guidance to eat 2-3 servings/week of a variety of fish lower in mercury 1.

From the Research

Harms of a Diet High in Tuna

• A diet high in tuna can pose health risks due to the presence of methylmercury (MeHg) and other toxic elements 2, 3.
• Methylmercury is a toxic substance that can cause neurological disorders and developmental problems, especially in children exposed in utero 4, 5.
• The bioaccessibility of MeHg in tuna is relatively low, but still poses a risk, especially for pregnant and nursing women who consume raw, boiled, or grilled tuna more than once a month 2.
• Canned tuna also contains MeHg, but the risk is lower compared to raw or cooked tuna, and a weekly meal of canned tuna is considered to have a very low risk 2.
• Other toxic elements such as cadmium (Cd), lead (Pb), and nickel (Ni) have been found in canned tuna, but their non-carcinogenic health risks are considered low for adults and children 3.
• However, the target hazard quotient (THQ) for MeHg in canned tuna was found to be higher than 1 for adults in some countries and for children in several countries, indicating a potential health risk 3.
• Mercury toxicity can cause a wide range of clinical presentations, including neurological, renal, respiratory, immune, dermatologic, reproductive, and developmental problems 4, 6, 5.
• Diagnosis of mercury toxicity can be challenging, but effective therapies have been described, including the use of chelating agents in cases of symptomatic acute mercury intoxication 4, 6, 5.