Hardly anyone talks about folic acid side effects.

Folic acid is not some major block buster drug having a list of dangerous side effects longer than its benefits.

According to WebMD, folic acid side effects can increase cancer risks, possible anemia, heart attacks and worsening of seizures but while these are great to know, these are not the folic acid side effects I want to share with you.



Why is no one talking about what I am about to show you?

Likely because you have to really, REALLY – dig for them.

Published literature contains very little on the side effects of folic acid. In fact, using that term won’t get you much.

Instead of searching for ‘folic acid side effects’ to get you the information you want, you need to be creative.

Let’s walk through this step by step.

It will be worth your while…


MTHFR testing has exploded globally. This is the gene which is used by the liver to perform methylation and must be working properly to convert leafy greens containing folate into the usable methylfolate or 5-MTHF.  Your body needs methylfolate to make normal red blood cells and prevent anemia aswell as being involved in brain chemistry and how DNA is used to rebuild the body constantly.

The positive finding is triggering a flurry of 5-MTHF supplementation or prescriptive medication. This is the inappropriate response. MTHFR variants have been present for countless generations.

The increase in cardiovascular diseases, congenital birth defects, infertility, recurrent miscarriages are NOT a result of the MTHFR variant.

It is a result of the environmental impact on MTHFR expression.

MTHFR is unable to handle the current present-day load.

A big factor weighing down MTHFR:

Folic acid.

See in the following folate pathway map , you can see that folic acid inhibits the DHFR enzyme on the way down and through to the ultimate purpose of the folate pathway.. creating methylfolate (5MTHF) and then MTR.




Whole Food to Processed Food

Plants grew and provided natural forms of folate. We harvested the fresh plants and utilized them immediately in various ways. Salads, steamed, dried, baked. In this manner, we received the nutrients as offered by the plant itself. One such nutrient provided by plants – especially leafy greens – is folate.

Folate comes from the Latin root ‘folium, which means leaf.

This powerful nutrient provides one of the most fundamentally important compounds in human biochemistry – the methyl group.

Access to these foods changed during the industrialised era. Instead of fresh breads baked daily, big business looked for ways to mass produce. The issue with mass production of finished food products, such as bread, was shelf life. It was found that if the outer parts of the grains were stripped off and milled, shelf life was extended dramatically.

The result of extended shelf life led to a surge in production and profits. It also led to a surge in birth defects and medical issues.

The Rise of Folic Acid

Instead of fixing the solution by reverting back to whole grains and fresh food, an artificial nutrient was created and added to these processed foods.

Folic acid.

In the rush to get folic acid to market, it was tested only on rats. It turns out that rats have a high ability to convert folic acid into a more bioavailable form of folate – dihydrofolate.

We are not using folic acid in rats. We are using it in humans.

This synthetic nutrient has indeed proven to reduce some incidences of birth defects and signs of folate deficiency.

It hasn’t done it successfully enough.

So, what we are finding now is that folic acid is actually harming us.

Folic acid is doing it quietly and insidiously.

Folic Acid: It’s Not the Same

Folic acid has no known physiological effect on human biochemistry.


While folic acid looks similar to natural folate, it is not close enough. Synthetic folic acid is lacking the body’s most fundamental biochemical compound – a methyl group.

To convert folic acid into methylated folate requires a) multiple functional genes producing b) functional enzymes which requires c) adequate cofactors. This is difficult enough. It is not all. The enzymes produced must also be in an environment free of compounds which interfere with their function – such as medications, heavy metals, cytokines, chemicals.

While rats can convert folic acid into dihydrofolate quickly and successfully, human biochemistry does not.

Only 200 mcg of folic acid can move through a human enzyme called DHFR. This is in humans who have a functional DHFR gene. There are known DHFR variants which lead to a further significant reduction in function. What does this mean? It means that folic acid is even less effective.

We made a dangerous assumption. We assumed since rats can convert folic acid easily into dihydrofolate, humans can too.

Since humans cannot convert folic acid effectively, the excess leads to high amounts of what is known as unmetabolised folic acid in the blood. Unmetabolised folic acid is folic acid.

Unmetabolised Folic Acid: It’s Harmful

Here are the reasons why unmetabolised folic acid is harmful:

  • Has no physiological benefit to the host until it is converted into dihydrofolate
  • Folate transport proteins bind it preferentially over more reduced active folate
  • Folate receptors bind it preferentially over more reduced active folate
  • Contributes to a pseudo MTHFR deficiency due to enzymatic inhibition of MTHFR
  • Reduces DHFR enzymatic function which reduces biopterin recycling, thereby contributing to a biopterin deficiency
  • Masks a vitamin B12 deficiency

This combination of negative physiological effects of folic acid is extremely significant.

In sum, they lead to what is called a ‘functional folate deficiency.’

Determining a Folate Deficiency

Common labs which measure serum folate are measuring the entire folate pool in the blood.

One cannot assume that serum folate contains the most active form of folate – which it should. Over 80% of circulating folate should be L-5-methyltetrahydrofolate. This is far from what many individuals have circulating.

Serum folate consists of unmetabolised folic acid, dihydrofolate, tetrahydrofolate, folinic acid, L-5-MTHF. This is not clinically useful information except only in the case of frank folate deficiency when serum folate is low.

The only ways to determine a functional folate deficiency:

  • History: “How much folic acid are you taking?” and “How much processed food are you eating? (as folic acid is found in these)
  • Lab: Measuring ‘UMFA’ which is unmetabolised folic acid. Issue is labs do not measure this. They used to but stopped due to lack of demand. We need it back.
  • Lab: Measuring Cerebral folate which is quite invasive.

If cerebral folate deficiency is identified, prescribing folic acid to treat it is . . . contraindicated.


Folic acid is a known contraindication of cerebral folate deficiency.

This alone begs the question:

Why are we using folic acid at all?

Couldn’t we all be struggling with some level of cerebral folate deficiency?

Folate: It’s what we need

Folic acid served its purpose.

Industrialisation stripped grains of natural vitamins, oils and fiber. This led to a dramatic increase in miscarriages and birth defects. Governments had to do something. The solution chosen was not to revert back to using whole grains; it was to use synthetic man-made folic acid which has no physiological effect until it is metabolised into more reduced folates.

The use of folic acid absolutely did reduce the incidence of miscarriages and birth defects – in some. Not nearly enough especially in Hispanic populations.

The FDA is working on fortifying corn flour now with folic acid.

This is not the solution.

The solution is to use natural forms of folate which are readily available and nearly as inexpensive as folic acid.

Without the presence of folic acid, natural folates may:

  • Bind to folate transport proteins freely
  • Bind to folate receptors freely
  • Help synthesize biopterin
  • Not mask a vitamin B12 deficiency
  • Enhance cellular folate levels

Fixing the Folate Problem

Folic acid is mandated to be included in many processed foods by many countries around the world. Stopping this bad practice is not going to cease any time soon.

Thankfully, steps may be taken right now to optimise human folate levels:

  • Avoid processed foods containing synthetic folic acid
  • Consume whole foods containing natural folates
  • Avoid supplements containing folic acid.
  • Utilize supplements containing folinic acid (calcium folinate) and/or Methylfolate – 5MTHFACTIVE (aka L-5-MTHF, 6S-5-MTHF)
  • Consume organ meats such as liver (grass fed, younger animals)

While the above steps will indeed support one’s folate levels, it is not sufficient enough to make a difference across the globe.

Article by Dr Ben Lynch