As most cases of vitamin B12 deficiency or folate deficiency can be easily and effectively treated, complications are relatively rare.

However, in some cases complications can develop, particularly if you have been deficient in vitamin B12 or folate for some time.

Anaemia complications

Anaemia, regardless of what it is caused by, can lead to heart and lung complications as the heart struggles to pump oxygen to the vital organs.

Adults with severe anaemia are at risk of developing:

• tachycardia - an abnormally fast heart beat
• heart failure - where your heart does not pump blood around your body very efficiently

Vitamin B12 deficiency complications

A lack of vitamin B12 can cause the following complications:

Nervous system

A lack of vitamin B12 can affect your nervous system (the brain, nerves and spinal cord). For example, you may experience:

• vision problems
• memory loss
• paraesthesia (pins and needles) - a prickling or tingling feeling in the arms, legs, hands or feet
• ataxia - the loss of physical coordination, which can affect your whole body and cause difficulty speaking or walking

Fertility

Vitamin B12 deficiency can sometimes lead to temporary infertility (an inability to conceive).

Neural tube defects

If you are pregnant, not having enough vitamin B12 can increase the risk of your baby developing a neural tube defect. Neural tube defects affect your baby's growth and development. Examples of neural tube defects include:

• spina bifida - where the baby's spine does not develop properly
• anencephaly - where the baby's brain and skull bones do not develop properly

Folate deficiency complications

A lack of folate can cause complications, some of which are outlined below.

Fertility

As with a lack of vitamin B12, a folate deficiency can also affect your fertility. However, effects are only temporary and can be reversed by using vitamin supplements.

Cardiovascular disease

Research has shown a lack of folate in your body may increase your risk of cardiovascular disease. Cardiovascular disease is a term that describes a number of health conditions that affect:

• your heart
• your blood vessels 
• the way blood circulates (flows) around your body 

Cancer

Research has shown folate deficiency can be linked to some cancers, such as stomach cancer. A lack of folate is never the sole cause of a cancer developing, but it may be a contributory factor.

Neural tube defects

As with a vitamin B12 deficiency, a lack of folate can also affect your baby's growth and development in the womb (uterus). This increases the risk of neural tube defects developing in the unborn baby, such as spina bifida.

Premature birth

As well as affecting your baby's growth, a lack of folate during your pregnancy may also increase the risk of your baby being born prematurely (before week 37 of the pregnancy).