It occurs endogenously in humans, where it has been identified in the hypothalamus, the limbic system, the pituitary, and even the gastrointestinal tract
A., Bhat, V
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Last reviewed: June 9, 2026 Last updated: June 9, 2026 Written by: Jay Hastings, CEO of PlexusDx Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations
Large population studies have shown that unexplained B12 levels above 813 pg/mL are associated with an increased risk of cancer diagnosis within one year, though the absolute risk for any individual is still relatively low