1.6.5 Folate (folic acid, vitamin B9 )
Folate is a generic name for a group of related compounds. The name ‘folate’ was based on the word ‘foliage’, after it was identified in a crude extract from spinach, though it is also found in liver, other green vegetables, oranges and potatoes and it is often added to breakfast cereals (usually listed as folic acid). Folate is less sensitive to heat than many of the B vitamins, though it is destroyed if food is reheated or kept hot for long periods. Folate is involved in amino acid metabolism, but its crucial role is in cell division, since it is used in DNA synthesis. So deficiency of folate has its major effect on dividing cells, especially those in the bone marrow (which produces red blood cells) and those lining the digestive system. Failure of normal cell division in the cells lining the digestive system can lead to loss of appetite, nausea and diarrhoea, and soreness in the mouth. Failure of normal cell division in the bone marrow leads to a type of anaemia called megaloblastic anaemia, where large, immature blood cells which do not have the normal oxygen-carrying capacity, are released into the circulation. After iron deficiency, folate deficiency is the next most common cause of anaemia.
Due to the huge amount of cell division that goes on in the first few months of pregnancy, pregnant women need as much as five times more folate than the normal daily requirement. Up to 25% of women would show changes in their bone marrow that are characteristic of folate deficiency if they did not increase their intake. Folate also appears to be important around the time of conception. For this reason, women planning to become pregnant are now encouraged to take folate supplements for about three months before conception and for the first three months of pregnancy. There appears to be a link between lack of folate and neural tube defects such as spina bifida, where the spinal cord does not develop correctly in the early fetus. Several studies have shown that giving folate supplements to women who have previously given birth to a child with a neural tube defect can reduce the risk of the same problem arising in a subsequent pregnancy by almost 75%.
There is some evidence that folate deficiency is also linked with increased risk of cardiovascular disease and with cancer, but more work is needed in both these areas. Alcohol affects the uptake of folate from the digestive system into the blood; so alcoholics are at risk of folate deficiency for this reason as well as because their diet may be lacking in folate. Other population groups who do not have a balanced diet, due to poverty, poor food choices, or illness, may also be at risk. Some commonly used drugs, including aspirin, indigestion remedies and the contraceptive pill, together with some antibiotics and anti-epilepsy drugs, may affect folate uptake too, and smokers may need additional folate. Chemotherapy drugs used in cancer treatment can also cause folate deficiency. In fact, folate deficiency is probably the most common vitamin deficiency seen in the developed world.