It sounds like you’re referring to a riddle-style fact, and the answer most commonly associated with this description is:

Peanuts

Why peanuts fit the description

• Responsible for over 200 deaths annually:
  Severe peanut allergies can trigger anaphylaxis, which leads to an estimated 150–200 deaths per year in the United States alone.
• Consumed by millions:
  Peanut butter, roasted peanuts, peanut oil, snacks, and candies are eaten worldwide every day.
• Deadliest in the world:
  Peanuts are often called one of the deadliest foods because even trace exposure can be fatal to someone with a severe allergy.

Important note

For most people, peanuts are safe and healthy. The danger applies only to individuals with a severe peanut allergy, which can cause life-threatening reactions.

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If you were actually referring to something else (for example: fugu fish, raw milk cheese, cassava, or wild mushrooms), just let me know and I’ll identify that one too.