Vitamin B complex contains all of the B's but for B12 you need a separate B12 methylcobalamin sublingual stand-alone. The reason being that B12 is a hormone rather than vitamin and is essential for neurological health if deficient:-
Symptoms of Vitamin B12 Deficiency - it is recommended that our result should be around 1,000. Methylcobalamin sublingual B12 should be chosen over cyanocobalamin B12.
If we don't have adequate vitamin B12 levels in our bloodstream, we might notice some of the following warning signs:
problems with your memory
lack of motivation
feelings of apathy
fatigue and a lack energy
tingling in your extremities
One of the most important functions of vitamin B12 is building the myelin which insulates and protects your nerve endings and allows them to communicate with one another.
If you're B12 deficient and your myelin is depleted, you can experience health problems as widespread as depression, dementia and even symptoms which mimic multiple sclerosis.
Depression is thought to be linked to a shortage of compounds called monoamines, which are manufactured by your central nervous system. Vitamin B12 helps your body make these compounds. There is also evidence high levels of homocysteine associated with B12 deficiency may promote depression.
Dementia and Alzheimer's
Research also indicates a B12 deficiency may lead to cognitive problems and reversible dementia in the elderly. This type of treatable dementia differs from Alzheimer's, however, B12 may play a role in this growing epidemic as well.
A study of over 100 senior volunteers showed older individuals with low levels of vitamin B12 are more apt to suffer from brain atrophy or shrinkage. Brain atrophy is a well-established characteristic of Alzheimer's disease.
If our B12 was quite low there is a possibility that we could have Pernicious Anaemia so GP should check for intrinsic factor which confirms P.A.