yes vitamin b12 deficiency causes severe depression. also thoughts like not being able to fulfil duties can induce guilt and worse depression. please take your friend to a psychiatrist for treatment with a combination of antidepressants and cognitive behavior therapy for best results. please continue his vitamin b12 replacement as going on. eating green vegetables and white meat like chicken and fish will help. for further information consult a psychiatrist online --> <link>
can vitamin b12 deficiency cause depression and anxiety?