Vitamin B12 deficiency: The tell-tale sign when waking up after a 'good' night's sleep

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B12 plays a "key" role in the production of red blood cells, it affects the amount of oxygen your body gets. So without the vitamin, which is found in lots of foods including meat, cheese and eggs, we can feel weak, struggle with movement and experience mood changes.

It also has a huge impact on our energy levels. Fatigue is a well known symptom of a B12 deficiency, but it could be easy to mistake just feeling tired or run down for a sign.

However, there is one way to tell in the morning if it is genuine fatigue - signalling a lack of B12. Health and wellbeing store, Holland and Barrett, explains: "The vitamin is important for your red blood cells. "When red blood cells are not able to divide, you can get a type of anaemia called megaloblastic anaemia. READ MORE: Sean Connery's widow on 'devastating effect' dementia had on Bond star - 'Took its toll'"Red blood cells also transport oxygen around your body, from your lungs. "Oxygen is important for your muscles and for recovering after exertion or exercise. "Vitamin B12 also helps metabolise protein, which is important for muscle building. "This means that no matter how much or how good a sleep you get at night and how much you work out during the day, you will still feel tired and weak if you are not getting enough B12. "Other signs of a B12 deficiency include pale or jaundiced skin. "With less red blood cells in your body, your skin loses some of that colour and looks paler," Holland and Barrett says. "The cells are also more fragile, and when a lot of them break down, you can have an excess of bilirubin. "Your liver produces this when it processes old blood cells.