Vitamin B12 is a crucial ingredient for the healthy running of the body, as it's needed to make red blood cells. Signs of a deficiency can develop very slowly, so it may be difficult to diagnose the condition.
People with undiagnosed symptoms should consider that they may have a vitamin B12 deficiency.
While it's unlikely that your symptoms are caused by the condition, there are still many people that have a lack of B12.
A quick blood test could reveal whether you should be adding more B12 to your diet.
You should consider speaking to a doctor about a B12 deficiency if you have an unexplained eye twitch.
The twitch in your eye may develop for no obvious reason, and it may only affect one of your eyes.
It won't necessarily be painful, but it will almost certainly be annoying, according to charity Patient Thyroid Advocacy.
You should speak to a doctor if your eye twitch won't go away after a few weeks.
It's not necessarily a sign of a vitamin B12 deficiency, but it's still worth getting checked out.
"If you have any unusual undiagnosed symptoms, perhaps you should consider whether you have a vitamin B12 deficiency," said the charity.
"B12 deficiency sometimes goes undiagnosed until the symptoms become moderate to severe, although this is not necessarily the fault of the medical profession.
"Eye twitch, usually in one eye or the other [may be a sign].
"It can occur on the eyelid or just below the eye. This is not usually painful, just annoying."
Eye twitches are very common, and they're rarely a sign of anything serious.
They're usually caused by stress or anxiety, as well as tiredness.
The best way to get rid of an eye twitch is to get plenty of rest, and to find new ways of relaxing.
You should also avoid drinking lots of alcohol, tea and coffee.
Some patients have also reported difficulty walking, vision disturbances, and mouth ulcers.
You should speak to a doctor if you're worried about vitamin B12 deficiency symptoms.
But you can top up on the vitamin by eating certain foods.
The best sources of vitamin B12 include beef, liver, dairy foods, eggs, and salmon.