Vitamin B12 deficiency symptoms occur when a person lacks the vitamin in their diet. Vegans and vegetarians can be at risk because the best sources of B12 are from foods of an animal origin. Certain medical conditions can also affect a person's absorption of B12 from foods, such as pernicious anaemia. Vitamin B12 is vital for the production of red blood cells and keeping nerves healthy.
If a person lacks B12, their red blood cell count will be low and their nerves can become damaged.
Vitamin B12 deficiency, left untreated, can lead to serious complications including temporary infertility and loss of physical co-ordination.
But these complications can be avoided if you spot the symptoms of vitamin b12 deficiency early enough.
One symptom which is not recognised as one of the main symptoms of vitamin B12 deficiency, but has been demonstrated in studies to be a sign, is trouble sleeping.
One small-scale study found two patients who suffered disrupted sleep-wake patterns found improved sleep after taking daily dosses of vitamin B12.
The patients were administered 1.5mg of vitamin B12 a day.
A good therapeutic effect lasted for more than six months while one of the patients - a 55-year-old man who suffered from delayed sleep phase syndrome since the age of 18 - was on the medication.
More general symptoms of vitamin B12 deficiency are listed by the NHS:
Bupa adds: "If you have vitamin B12-deficiency anaemia, you may also look pale or jaundiced (have a yellowy tinge to your skin and the whites of your eyes).
"As well as the symptoms of anaemia, vitamin B12-deficiency may cause symptoms related to your nerves. This is called vitamin B12 neuropathy. It may affect your movement and sensation, especially in your legs, cause numbness or pins and needles and decrease your sensitivity to touch, vibration or pain. It can also cause confusion, depression, poor concentration and forgetfulness.
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