Folic acid - basics

Folic acid (also known as vitamin B₉,^[3] vitamin B_c^[4] orfolacin) and folate (the naturally occurring form), as well aspteroyl-L-glutamic acid, pteroyl-L-glutamate, andpteroylmonoglutamic acid^[5] are forms of the water-soluble vitamin B₉. Folic acid is itself not biologically active, but its biological importance is due to tetrahydrofolate and other derivatives after its conversion to dihydrofolic acid in the liver.^[6]

Vitamin B₉ (folic acid and folate inclusive) is essential to numerous bodily functions. The human body needs folate to synthesize DNA, repair DNA, and methylate DNA as well as to act as a cofactor in biological reactions involving folate.^[7]It is especially important in aiding rapid cell division andgrowth, such as in infancy and pregnancy, as well as in "feeding" some cancers. While a normal diet also high in natural folates may decrease the risk of cancer, there isdiverse evidence that high folate intake from supplementation may actually promote some cancers as well as precancerous tumors and lesions. Children andadults both require folic acid to produce healthy red blood cells and prevent anemia.^[8]

Folate and folic acid derive their names from the Latin wordfolium (which means "leaf"). Leafy vegetables are a principal source, although in Western diets fortified cereals and bread may be a larger dietary source.

A lack of dietary folic acid leads to folate deficiency which is uncommon in normal Western diets. Failures to replenish one's folates might not manifest themselves as folate deficiency for 4 months because a healthy individual has about 500–20,000 mcg^[9] of folate in body stores.^[10] This deficiency can result in many health problems, the most notable one being neural tube defects in developing embryos. Common symptoms of folate deficiency include diarrhea, macrocytic anemia with weakness or shortness of breath, nerve damage with weakness and limb numbness (peripheral neuropathy)^{[citation needed]}, pregnancy complications, mental confusion, forgetfulness or other cognitive declines, mental depression, sore or swollen tongue, peptic or mouth ulcers, headaches, heart palpitations, irritability, and behavioral disorders. Low levels of folate can also lead to homocysteine accumulation.^[7]DNA synthesis and repair are impaired and this could lead to cancer development.^[7] Supplementation in patients withischaemic heart disease may also lead to increased rates of cancer.^[11]

[edit]Dietary reference intake

Because of the difference in bioavailability between supplemented folic acid and the different forms of folate found in food, the dietary folate equivalent (DFE) system was established. One DFE is defined as 1 μg (microgram) of dietary folate, or 0.6 μg of folic acid supplement.

The Dietary Reference Intake (DRIs) were developed by the United States National Academy of Sciences to set reference values for planning and assessing nutrient intake for healthy people. DRIs incorporate two reference values, the Reference Daily Intake (RDI, the daily intake level that is adequate for 97–98% of the population in the United States where the standards were set) and tolerable upper intake levels (UL, the highest level of intake which is known to avoid toxicity). The UL for folate refers to only synthetic folate, as no health risks have been associated with high intake of folate from food sources.^[12]

[edit]Folate in foods and other sources

Certain foods are very high in folate:

• Leafy vegetables such as spinach, asparagus, turnip greens
• Legumes such as dried or fresh beans, peas and lentils
• Egg yolks.^[13]
• Baker's yeast
• Fortified grain products (pasta, cereal, bread); some breakfast cereals (ready-to-eat and others) are fortified with 25% to 100% of the recommended dietary allowance (RDA) for folic acid
• Sunflower seeds
• Liver and liver products also contain high amounts of folate
• Kidney^[13]

Moderate amounts:

• Certain fruits (orange juice, canned pineapple juice, cantaloupe, honeydew melon, grapefruit juice,banana, raspberry, grapefruit and strawberry) and vegetables (beets, corn, tomato juice, vegetable juice,broccoli, brussels sprouts, romaine lettuce and bok choy),^[14] beer.^[15]

A table of selected food sources of folate and folic acid can be found at the USDA National Nutrient Database for Standard Reference.^[16] Folic acid is added to grain products in many countries, and, in these countries, fortified products make up a significant source of the population's folic acid intake.^[17] Because of the difference in bioavailability between supplemented folic acid and the different forms of folate found in food, the dietary folate equivalent (DFE) system was established. 1 DFE is defined as 1 μg of dietary folate, or 0.6 μg of folic acid supplement. This is reduced to 0.5 μg of folic acid if the supplement is taken on an empty stomach.^[18]

Folic acid naturally found in food is susceptible to high heat and ultraviolet light, and is soluble in water.^[19] It is heat-labile in acidic environments and may also be subject to oxidation.^[19]

Some meal replacement products do not meet the folate requirements as specified by the RDAs.^[20]

• 

  Spinach

 
• 

  Aspargus

 
• 

  Beans

 
• 

  Peas

 
• 

  Lentils

 
• 

  Egg yolk

 
• 

  Baker's yeast

 
• 

  Fortified grain

 
• 

  Sunflower seeds

 
• 

  Turnips

[edit]