Vitamin B9 is an essential nutrient that naturally occurs as folate.
It serves many important functions in your body. For example, it plays a crucial role in cell growth and the formation of DNA.
Low levels of vitamin B9 are associated with an increased risk of several health conditions, including:
- Elevated homocysteine. High homocysteine levels have been associated with an increased risk of heart disease and stroke (1Trusted Source, 2Trusted Source).
- Birth defects. Low folate levels in pregnant women have been linked to birth abnormalities, such as neural tube defects (3Trusted Source).
- Cancer risk. Poor levels of folate are also linked to increased cancer risk (4Trusted Source, 5Trusted Source).
For these reasons, supplementing with vitamin B9 is common. Fortifying food with this nutrient is mandatory in many countries, including the United States and Canada.
Vitamin B9 is an essential nutrient that’s mainly present as folate and folic acid. It’s commonly taken in supplement form and even added to processed food in North America.
What is folate?
Folate is the naturally occurring form of vitamin B9.
Its name is derived from the Latin word “folium,” which means leaf. In fact, leafy vegetables are among the best dietary sources of folate.
Folate is a generic name for a group of related compounds with similar nutritional properties.
The active form of vitamin B9 is a folate known as levomefolic acid or 5-methyltetrahydrofolate (5-MTHF).
In your digestive system, most dietary folate is converted into 5-MTHF before entering your bloodstream (6Trusted Source).
Folate is the naturally occurring form of vitamin B9. Before entering your bloodstream, your digestive system converts it into the biologically active form of vitamin B9 — 5-MTHF.
What is folic acid?
Folic acid is a synthetic form of vitamin B9, also known as pteroylmonoglutamic acid.
It’s used in supplements and added to processed food products, such as flour and breakfast cereals.
Unlike folate, not all of the folic acid you consume is converted into the active form of vitamin B9 — 5-MTHF — in your digestive system. Instead, it needs to be converted in your liver or other tissues (5Trusted Source, 6Trusted Source).
Yet, this process is slow and inefficient in some people. After taking a folic acid supplement, it takes time for your body to convert all of it to 5-MTHF (7Trusted Source).
Even a small dose, such as 200–400 mcg per day, may not be completely metabolized until the next dose is taken. This problem may become worse when fortified foods are eaten along with folic acid supplements (8Trusted Source, 9Trusted Source).
As a result, unmetabolized folic acid is commonly detected in people’s bloodstreams, even in the fasted state (10Trusted Source, 11Trusted Source, 12Trusted Source).
This is a cause for concern, as high levels of unmetabolized folic acid have been associated with several health problems.
However, one study suggests that taking folic acid along with other B vitamins, particularly vitamin B6, makes the conversion more efficient (10Trusted Source).
Folic acid is a synthetic form of vitamin B9. Your body does not convert it into active vitamin B9 very well, so unmetabolized folic acid may build up in your bloodstream.
Is unmetabolized folic acid harmful?
Several studies indicate that chronically elevated levels of unmetabolized folic acid may have adverse health effects, including:
- Increased cancer risk. High levels of unmetabolized folic acid have been associated with increased cancer risk. However, no evidence proves that unmetabolized folic acid plays a direct role (13Trusted Source, 14Trusted Source, 15Trusted Source).
- Undetected B12 deficiency. Among elderly people, high folic acid levels can mask vitamin B12 deficiency. Untreated vitamin B12 deficiency may increase your risk of dementia and impair nerve function (16Trusted Source, 17Trusted Source).
Even a small, daily dose of 400 mcg may cause unmetabolized folic acid to build up in your bloodstream (9Trusted Source, 18Trusted Source).
Although high folic acid intake is a concern, the health implications are unclear, and further studies are needed.
Researchers are concerned that high levels of unmetabolized folic acid may negatively affect health, but more studies are needed before any strong conclusions can be reached.
What is the healthiest source of vitamin B9?
It’s best to get vitamin B9 from whole foods.
High-folate foods include asparagus, avocados, Brussels sprouts, and leafy greens like spinach and lettuce.
However, for some people, such as pregnant women, supplements are an easy way to ensure adequate vitamin B9 intake.
Folic acid is the most common supplemental form of vitamin B9. It can be purchased at many drug stores, as well as online.
Other supplements contain 5-methyltetrahydrofolate (5-MTHF), also known as levomefolate, which is considered an adequate alternative to folic acid (19Trusted Source, 20Trusted Source, 21Trusted Source, 22Trusted Source).
Supplemental 5-MTHF is available in the form of levomefolate calcium or levomefolate magnesium. It’s sold under the brand names Metafolin, Deplin, and Enlyte and available online.
The healthiest dietary sources of vitamin B9 are whole foods, such as leafy green vegetables. If you need to take supplements, methyl folate is a good alternative to folic acid.
The bottom line
Folate is the natural form of vitamin B9 in food, while folic acid is a synthetic form.
High intake of folic acid may lead to increased blood levels of unmetabolized folic acid. Some researchers speculate that this may have adverse health effects over time, but further studies are needed before solid conclusions can be reached.
Alternatives to folic acid supplements include 5-MTHT (levomefolate) or whole foods, such as leafy greens.