Vitamin B12 and folate explained: what they do

Vitamin B12 and folate are two vitamins the body needs to make healthy red blood cells and to keep the nervous system working. They are often tested alongside iron because a lack of either can also cause anaemia, and the symptoms can look similar.

What happens with too little

The NHS says a lack of B12 or folate can cause the body to make red blood cells that are unusually large and do not work properly. Those cells carry oxygen using haemoglobin, so there is less oxygen available to the body.

Symptoms the NHS lists

• Extreme tiredness and low energy.
• Pins and needles, muscle weakness and problems with vision.
• A sore, red tongue and mouth ulcers.
• Changes in mood and thinking, from low mood or anxiety to confusion, and problems with memory and judgement.

The NHS notes that some of these can happen without anaemia, and that diagnosing a lack of B12 or folate promptly matters because some complications can be permanent.

Causes the NHS describes

• Pernicious anaemia, where the immune system attacks cells in the stomach so that B12 is not absorbed. It is the most common cause of B12 deficiency in the UK.
• Diet, which is an uncommon cause but possible, for example on a vegan diet without B12 supplements or fortified foods.
• Some medicines, including some anti-seizure drugs and acid-reducing medicines, which can reduce absorption.
• Age: the NHS says B12 deficiency is more common in older people.

Units differ between countries

B12 is printed as pg/mL on many United States reports and as pmol/L on many in the UK and Europe. Folate is printed as ng/mL on many reports in the United States and as nmol/L elsewhere. The free converters at ferrolady.com/tools change only the unit a number is written in. FerroLady can record B12 and folate results with the unit printed on your report.