Your genetics do not cause the autoimmune attack, but they do shape how efficiently you absorb, transport, and use B12 once it is in your system
Vitamin B12 Deficiency Is Rare The liver can store excess vitamin B12, and only trace amounts are lost through daily bodily functions such as urination, perspiration, and defecation
Typically administered as a weekly intramuscular injection

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High intakes of vitamin B12 have been linked to a lower risk of depression, which can be a major cause of sleep disorders like insomnia
After that window, the preservative action may not be sufficient to prevent contamination, and you should discard any remaining solution