Difference Between Folate and Folic Acid
Folate is a general term used to characterize a group of water soluble B vitamins. Folic Acid is the oxidized, synthetic form of this vitamin. Folic acid is a more stable form so it commonly used in fortified foods and supplements. When you see the term Folate, it refers to the compound that is naturally found in food.
For some, the synthetic folic acid undergoes a series of changes before it is converted into the usable L-Methylfolate. For others it accumulates in the body and increases toxicity levels, leading to a myriad of health concerns.
Folic Acid Cycle
Folic Acid – Dihydrofolate – Tetrahyrdrofolate – 5, 10 Methylene THF – L-Methylfolate
MTHFR is a genetic disorder that inhibits the efficiency of the methylation cycle, in turn affecting the body’s ability to metabolize certain substances and synthesize certain nutrients. Individuals with this genetic dysfunction cannot convert Folic Acid into the usable form of L-Methylfolate. This causes a buildup of folic acid in the body, causing a toxic reaction and significantly increased homocysteine levels. 
Folic Acids Beginning
Folic acid was first synthesized in 1943 but was introduced as a mandatory food fortification in 1998. This was because of the evidence that suggested that folic acid had benefits for developing fetus’ neural tubes. Helping to prevent Neural Tube Defects in newborns.
This instances of Neural Tube Defects promptly fell once folic acid was introduced in fortified foods. There were however numerous health concerns associated with excess folic acid intake, including an increased risk of cancer. [2,3]
Dangerous Side Effects of Folic Acid
Excess folic acid in the body is associated with a decrease in natural killer cytotoxicity. Since natural killer cells play a key role in tumor cell destruction, it is thought that folic acid intake can promote tumor growth. 
A truly alarming side effect of folic acid among the elderly is the effects it has on the cognitive function of an individual. One study showed that elderly individuals taking 400 mcg of folic acid daily had a significantly increased rate of cognitive decline as oppose to those who didn’t supplement with folic acid. It has also been associated with anemia and cognitive impairment among the elderly. 
Women who are planning on conceiving a child should supplement their folate levels both before and after conception. Choosing a supplement that contains 5-MTHF or 5-Methyltetrahydrofolate is the best option. Avoid any supplements or foods that use folic acid. Supplementing 400-1000 mcg of 5-Methyltetrahydrofolate daily is a good idea for women planning on getting pregnant and those who are with child.
Added Dangers of Folic Acid with MTHFR
One of the major concerns for those with MTHFR is their inability to synthesize an adequate amount of Glutathione. Coupled with the increased toxicity due to excess folic acid intake the body is left defenseless against the flood of toxins. This can lead to any number of health conditions beyond cognitive impairment and the development of cancer, including: impaired immune function, decreased liver function, increased risk of heart disease, neurological issues and a plethora of other concerns.
Benefits of Folate for MTHFR
If you suffer from MTHFR it is crucial to avoid folic acid entirely. It is also important to ensure you supplement your folate levels with 5-Methyltetrahydrofolate as well as natural food sources like leafy vegetables and liver. [6,7]
Supplementing with the correct form of folate can yield immense health benefits, especially for those of us with MTHFR. The other side of that coin, the wrong form (folic acid) can cause severe health problems. Always read your labels and supplement smart, and of course, work closely with your healthcare professional.