Brazil nuts are very high in selenium, with one nut typically providing about 50–100 mcg, while the recommended daily intake is around 55 mcg and the safe upper limit is about 400 mcg, so usually 1–2 nuts per day are enough to meet needs without risking excess. They support thyroid function, immune health, and antioxidant protection due to their selenium content, but eating too many regularly can lead to selenium toxicity, which may cause symptoms like nausea, hair loss, brittle nails, and digestive issues, so moderation is important for safe long-term benefits.