So you are worried.  You feel tired all the time, and yet you can't sleep.  You get tingling or headaches, memory problems, and so on.  Could you be short of Vitamin B12?

Well it depends.  Doctors use a process called Differential Diagnosis to decide what the problem is.  That means, they get an overall picture of your health and your symptoms, which gives them a start point.  Could you be worried about money or a family member?  Do you have a virus?  Do you eat the wrong things or nothing at all?  Do you have a terrible but very rare disease?  Then they ask questions which help them decide which of these solutions is right, and your answers may take them down another route entirely.  It always helps your doctor if you have a symptoms diary, a list of your symptoms, how bad they were and when they occurred.  Readers keep asking me to prepare a downloadable symptoms diary - coming "soon".

B12 deficiency is actually very easy to diagnose, but we've complicated things to the point where it isn't your doctor's first thought.  Do you have pernicious anaemia*, or Crohn's disease, or Alzheimer's, or depression?  Do you have sciatica or Bell's palsy?  ME or MS?  All of these are descriptions of symptoms, and the treatment for most of them is simply medication that stops you feeling the symptoms rather than making you better.  But what if all of these (and a whole lot more besides) could actually be CURED?

That's where your doctor needs to go back to his or her basic biochemistry training, and think more deeply.

Vitamin B12 is a very basic vitamin, needed by animals from well before mammals evolved for a number of really key functions.

What does B12 do?

Vitamin B12 is needed for energy production, for lipid metabolism, some mood chemicals, for DNA transcription and for removal of toxins especially heavy metals.

The bit of lipid metabolism that Vitamin B12 is needed for affects some key areas of your body - nerve transmission (both motor nerves ie how you control your muscles, and sensory nerves ie what you feel); hormones and the endocrine system (including most significantly female fertility); the immune system; and your digestive system.

So if you have problems with your nerves (lipid metabolism) and are tired all the time (often energy production), then your problem could either be because you have two diseases (one in each area) simultaneously, or you have a single problem which affects both systems.  Similarly if you have regular memory problems (lipid metabolism) and menorrhagia (heavy periods, bleeding between periods, infertility - also lipid metabolism but a totally different aspect) then you could have two simultaneous diseases or you could have a common cause.

Occam's Razor

Your doctor needs to work out what to treat, by working out what the problem is.  Occam's Razor is a simple principle - the doctor thinks in their head about all the possibilities, then excludes the least likely and examines the remaining 2 or 3 in more detail.  It is the basis of the differential diagnosis.  In the above examples, getting two simultaneous diseases is fairly unlikely, so the doctor should look for a common cause.  

In 2010, we built a table of  Signs and Symptoms so you could see how you score.  2012 we've updated the diagnosis, but it is quite difficult to change the web page so i haven't done it yet - 2010's table will still give good results. 

Essentially, you tick off the symptoms that you observe, and it gives you a score - a likelihood that your symptoms are ue to B12 deficiency.  A lot of symptoms - more likely that you have B12 deficiency.  Only one symptom - you probably have a single specific cause such as stress or a pinched nerve.

On the next page, we look at how your doctor will tackle it.