For how we live.
"Brain fog" is a lay term for trouble concentrating and remembering, not a disease. Common drivers include poor sleep, low mood, the menopause transition, thyroid or B12 problems, and the tail of an infection.
A limb that has "gone to sleep" is brief pressure on a nerve and clears in minutes. Tingling that is persistent or spreading can mean carpal tunnel, diabetes or low B12; sudden one-sided numbness is an emergency.
A varied diet covers most of the 13 essential vitamins. The evidence-based exceptions are specific: vitamin D is hard to get from food, older adults and vegans need B12, and folic acid is advised before pregnancy.
Classic B12 deficiency is relatively uncommon, but it clusters: in people over 50 whose absorption fails, in vegans whose intake does, and around metformin, acid-lowering drugs and stomach surgery.
Adults need about 2.4 micrograms a day, and most meat-eaters get it easily. Real deficiency clusters in older people, whose absorption fails, and in vegans, whose intake does.
Among 3,032 couples sampled before conception, higher maternal and paternal vitamin B12 both tracked with lower predicted birth-defect prevalence. The paternal pattern was weaker, and this is observational.
A Shanghai study of 3,032 couples measured nutrients before conception. Predicted birth-defect prevalence fell across maternal B12 levels — and, more weakly, across paternal ones.