Vitamin B12

Methylmalonic acid should not be used to rule out B12 deficiency. Normal serum B12 can coexist with depleted cerebrospinal fluid B12 in early cognitive decline. Serum B12 levels below 500 pg/mL are associated with neuropsychiatric symptoms according to the article. The article favors sublingual B12 over oral capsule or liquid delivery because sublingual administration bypasses gastrointestinal absorption. B12 deficiency is described as the most common cause of elevated homocysteine. B12 deficiency may present with psychiatric, cognitive, fatigue-related, and neurological symptoms. B12 supplementation is presented as having a broad safety margin at therapeutic doses.