The big problem with B12 deficiency is that the symptoms are really common, and could be caused by something else instead.
If you don’t sleep, you will feel tired. If you are stressed, then you won’t sleep and you will feel tired. But for some people, there’s nothing to be stressed about and they spend hours asleep, and still wake up tired; or they can manage in the morning but are really tired by early afternoon.
Have you checked whether you are allergic to something? Allergies (such as to gluten, milk, house dust) can cause fatigue.
But it could be B12 deficiency (sufferers describe it as ‘overwhelming tiredness’ and ‘the sighs’). The great thing about B12 deficiency is that it’s easily cured (take some supplemental B12), and the cure is completely safe. You can take some supplements and see if this makes a difference, and if it doesn’t, go down the allergy route. The not so great thing is that there are many different forms of B12 to take as supplements, and different ones seem to work on different people. More on this later.
This is one of the classic signs of neuropathy, neuropathy of the sensory nerves in the peripheral nervous system. There aren’t too many reasons why someone would suffer from neuropathy, but B12 deficiency is one of the most common causes http://www.b12d.org/overview/symptomspns.
Without B12, your natural body repairs of the myelin sheath (the insulation that goes around each nerve axon to make sure it carries its signal and only its signal) don’t work properly. You lose insulation. This can mean that the nerve doesn’t carry its signal to the brain, meaning numbness in the affected area (you can’t feel pain or pressure or heat in a particular bit of skin or on your foot, for example). Alternatively (or even at the same time), it can mean that signals travelling down neighbouring nerve axons trigger a signal in this nerve axon. Since the neighbouring nerve axon can connect to an entirely different part of the body, it results in a funny pattern of signals to your brain that your brain interprets as pins and needles.
The nerve axons most likely to be affected are the longest ones, ie the ones that go to the parts of your body furthest from your brain, in other words the nerves in feet and hands, which is why this often shows up in feet and hands. However a symmetrical problem could be due to pinched nerves, and B12 deficiency is more likely to give asymmetric symptoms (ie one side hand and foot shows it worse than the other).
One of the classic symptoms of B12 deficiency 100 years ago was a strange walk, variously described as walking like a crab, or appearing drunk without drink. It isn’t at all like being drunk - there’s none of the pleasure. But it’s the same cause as above - weakness (which can show up as ‘foot drop’, or paralysis/ occasional paralysis) is when the signal from the brain doesn’t get through because the nerve is damaged.
The most common one we see is low cortisol, where you can’t wake up in the morning because your natural cycle of cortisol - high in the morning to wake you up - doesn’t happen. But patients have described having their infertility or heavy periods/ bleeding between periods cured with B12 supplements; both hypothyroidism and hyperthyroidism have been cured; and there are tens of hormones each with different jobs to do around the body, which could show up and make you feel terrible if they aren’t working the way God intended.
I mentioned above that B12 is completely safe to take supplements - it doesn’t affect any medicine you may be taking (don’t stop your medication until/ unless your doctor says you should, even if the symptoms go away with B12 supplements), and you can take huge doses without any harm except that if you don’t need it, you’ve spent some money you didn’t need to. Mice have been tested with 100 million times the pharmacological dose, with no ill effects.
The guidance says that the body only needs around 35mcg per day of B12. That’s great if you are healthy and not sensitive to B12 deficiency, but there are people who need 1000mcg/day or even more in tablets to function, and some people who are injecting methylcobalamin every week or twice a week because they are really sick.
Just remember - cyanocobalamin is probably not going to work, if you are buying tablets then get the ones that contain methylcobalamin or adenosylcobalamin (or both), or hydroxocobalamin. You may need other vitamins and minerals as supplements - I recommend a one-a-day multivitamin multimineral which are fairly cheap, and they may have different mixes of vitamins and minerals but the differences are fairly unimportant. They don’t have enough B12 in though, you will need more B12 on top.