Methylmercury half-life in the human body: ~50 days. Daily tuna consumption means mercury intake outpaces excretion. Light tuna (skipjack): lower mercury (0.12ppm) — 2-3 cans/week is the FDA safe limit for adults. Albacore: higher mercury (0.35ppm) — 1 can/week. Symptoms of mercury toxicity: numbness/tingling in hands/feet, memory problems, vision changes, coordination issues. These develop over months — you won't notice until levels are already high.
Tuna is high in selenium (80μg/can — 146% DV). Selenium binds mercury (Hg-Se complex) and reduces its toxicity. This is why populations eating high-fish diets (Japanese, Inuit) have lower mercury toxicity than predicted. Selenium doesn't ELIMINATE the risk — it reduces it.
Daily tuna would provide 25g protein + omega-3 + selenium + B12 + vitamin D. These benefits are real. The mercury concern doesn't make tuna unhealthy — it makes FREQUENCY the issue. Tuna 1-2x/week = net health benefit. Tuna daily = net health risk from mercury.
✅ Safer Daily Alternatives
Sardines (lowest mercury of any fish — eat freely), wild salmon (very low mercury, farmed is fine too), anchovies, herring, mackerel (Atlantic, not king), trout, tilapia. These can be eaten daily with negligible mercury risk.