This site cites this specific source directly: National Institute on Aging, Memory Problems, Forgetfulness, and Aging.
Worth noting this is the one reference not tied to a specific ingredient — it addresses when memory changes warrant medical attention generally, directly supporting this site's own repeated red-flag guidance.
This site links to this source directly alongside its specific examples of worrying symptoms — worth checking it if you're uncertain whether your own or a family member's experience warrants medical attention.