Folates are compounds of pteroylglutamic acid (PGA)
that function as coenzymes in metabolic reactions involving the transfer
of single-carbon units from a donor to a recipient compound. Folate,
with vitamin B12, is essential for DNA synthesis, which is required for normal red blood cell maturation.2 Humans obtain folate from dietary sources including fruits, green and leafy vegetables, yeast, and organ meats.3 Folate is absorbed through the small intestine and stored in the liver.
Low
folate intake, malabsorption as a result of gastrointestinal diseases,
pregnancy, and drugs such as phenytoin are causes of folate deficiency.4 Folate deficiency is also associated with chronic alcoholism.5 Folate and vitamin B12
deficiency impair DNA synthesis, causing macrocytic anemias. These
anemias are characterized by abnormal maturation of red blood cell
precursors in the bone marrow, the presence of megaloblasts, and
decreased red blood cell survival.2
Since both folate and vitamin B12
deficiency can cause macrocytic anemia, appropriate treatment depends
on the differential diagnosis of the deficiency. Serum folate
measurement provides an early index of folate status3;
however, folate is much more concentrated in red blood cells than in
serum so the red blood cell folate measurement more closely reflects
tissue stores.5,6 Erythrocytes incorporate folate as they
are formed, and levels remain constant throughout the life span of the
cell. RBC folate levels are less sensitive to short-term dietary
effects than are serum folate levels. Red blood cell folate
concentration is considered the most reliable indicator of folate
status.3
Low serum folate during pregnancy has been associated with neural tube defects in the fetus.7,8
