Over the past few years, there’s been a shift towards a preference for the bioactive form of folate, 5-methyltetrahydrofolate (5-MTHF), rather than the synthetic folic acid in dietary supplements. While folic acid has long been the most common form of supplemental folate, it is a precursor to the bioactive form of folate, and many believe that taking the bioactive form leads to better health outcomes.
With the rising beliefs over the superiority of 5-MTHF to folic acid, it makes me curious as to the evidence behind it, so I did a deep dive into the literature to see what I could find. Here is a look at some of the latest research comparing folic acid and 5-MTHF supplementation.
What You Need to Know About Folate & Its Supplemental Forms
Before looking more closely at the research comparing the different forms of supplemental folate, there’s some important background information to review for the debate context.
First, a quick recap of folate’s important actions in the body:
- Cell division and tissue growth
- DNA and RNA synthesis (thymidylates and purines for nucleic acids)
- Homocysteine regulation through methylating homocysteine into methionine
- Metabolism of amino acids
- Methyl donor for more than 100 metabolic processes, including DNA, histone proteins, and neurotransmitters
- Methylation reactions of DNA
- Synthesis of glycine from serine
Folic acid is the synthetic version of folate found in fortified foods and supplements. For folic acid to become the active form of folate, 5-MTHF must undergo several molecular reactions in the liver. First, the 6-methylpterine moiety is catalyzed twice by dihydrofolate reductase (DHFR) to become dihydrofolate and then tetrahydrofolate. Then, tetrahydrofolate undergoes single-carbon transfer and transports it where serine hydroxymethyltransferase metabolizes it into 5,10-methylenetetrahydrofolate. Methylenetetrahydrofolate reductase (MTHFR) is the final step to create 5-MTHF.
Because it must undergo so many steps, anything that interrupts DHFR or MTHFR’s key enzymes may also lead to reduced bioavailability. There are common genetic SNPs that impact DHFR and MTHFR, with MTHFR polymorphisms more frequent. There’s a hypothesis that in individuals with these genetic polymorphisms, 5-MTHF supplementation is better because it bypasses the pathways requiring both. The human gut also converts dietary folates to 5-MTHF much easier than folic acid. One study shows large amounts of unmodified folic acid likely due to limited DHFR in mucosal cells.
The other main concern with folic acid is that long-term supplementation can increase unmetabolized folic acid levels that may negatively impact health. The research into these potential health concerns has yet to reach conclusive results. One study found that unmetabolized folic acid reduced natural killer cell (NK) cytotoxicity, impacting the immune system and increasing the risk and severity of infections. Another study found an increased risk of developing food allergies in children who had higher levels of unmetabolized folic acid in the cord blood, even though they had lower total folate concentrations at birth. However, neither folate levels nor unmetabolized folic acid levels in infanthood or early childhood made any difference to food allergies’ increased risk.
A major concern regarding unmetabolized folic acid is that it increases the risk of cancer. However, studies remain inconclusive, and several have found no significant association, especially in countries without mandatory fortification. In a study looking at a population not living in mandatory folic acid fortification, there was no association between breast cancer risk and unmetabolized folic acid. A meta-analysis found no impact of folic acid on site-specific cancer incidence during the first five years of supplementation. Ultimately, more research is needed, especially in areas with mandatory folic acid fortification.
Although the evidence for health impacts remains inconclusive and undergoing, studies are consistent in demonstrating higher levels of unmetabolized folic acid (UMA) due to supplementation and fortification. In one study, after 6 months of folic acid supplementation, 29 percent of participants had detectable UMA, and after one year, 80.6 percent did. Using NHANES data from 2001-2002, researchers reported 38 percent of the study population had detectable levels of unmetabolized folic acid, with a significantly higher number of those taking folic acid supplementation but some from fortified food alone. Because folate supplementation is common in pregnancy to prevent neural cord defects, unmetabolized folic acid’s impact on infants is also a concern. There is evidence of unmetabolized folic acid in cord blood and serum of 4-day old infants, some of which were folic acid in the infant formula and fortified foods.
Fortification also adds to the potential for unmetabolized folic acid levels circulating, especially in those who supplement with folic acid. One study looked at blood samples from subjects before and after fortification and found an increase from 0.25 to 0.50 nmol/L in non-supplement users, and that in those who did supplement, the increase was from 0.54 to 0.68 nmol/L. When looked at from a different angle, the percentage of participants who had high circulating folic acid levels increased from 9.4 percent to 19.1 percent in the non-supplement users compared to 15.9 percent to 24.3 percent in the supplement group. There may be a dose-dependent relationship. One study found that it was at 400 ug daily folate in folate-saturated participants that led to detected levels of unmetabolized folic acid levels, while 200 ug or 100 ug did not.
Additional concerns about folic acid supplementation include its ability to mask a vitamin B12 deficiency, as well as the potential impact of unmetabolized folic acid on health.
The Evidence for Folic Acid and 5-MTHF
Some disclaimers need to be discussed before reviewing the evidence to find the superior supplemental form of folate. First, there are approximately 10 times as many studies on folic acid compared to 5-MTHF. For example, at the time of writing this article, on PubMed, if you search 5-MTHF, only 195 possible studies pop up. For 5-methyltetrahydrofolate, 1,523 results appear; when “5-methyltetrahydrofolate supplementation” is searched, 191 results are returned and 54 for 5-MTHF supplementation. Compare those numbers to the 51,562 results for folic acid, which is further reduced to 5,792 with the term folic acid supplementation. There are additional search terms one might use, some of the studies may be duplicates, and just because there are search results to those topics does not mean that all the studies apply to what we’re looking for. However, just looking at the number of results for those terms demonstrates a dearth of research into 5-MTHF in relation to folic acid. Much of that is simply due to a decades-long head start of research into folic acid compared to 5-MTHF.
A major percentage of folic acid research looks at its impact during pregnancy, especially to prevent neural tube defects. However, post-food fortification, the benefit of additional supplementation may not be as much. There’s also research into cognitive development and function as well as cardiovascular disease. Studies have also found folic acid supplementation reduces the risk of Alzheimer’s disease, preeclampsia, and stroke, to name a few.
With the popularity of 5-MTHF supplementation, more research has looked at the potential benefits, much of which falls along similar lines. For example, a non-extensive list of studies on 5-MTHF supplementation includes finding it:
- Helped treat schizophrenia
- Improved depression in the elderly
- Improved endothelial dysfunction in uremic patients who are on peritoneal dialysis, independent of homocysteine levels
- Improved infertility, including conception and term pregnancy, in couples with MTHFR genetic SNPs and a history of infertility or miscarriages
- Improved nitric oxide status and endothelial function in diabetic patients
- Improved red blood cell membranes in children with cystic fibrosis, along with vitamin B12 supplementation
- Reduced blood pressure, homocysteine, and insulin resistance with short term, high dose
- Reduced homocysteine levels, including in a cyclic routine
- Reduced oxidative stress that correlated with a nocturnal decline of blood pressure
- Reduced risk of preeclampsia in patients with a history of preeclampsia
While there is a lot of research focusing on one form of supplementation’s impact on health, many studies compare folic acid and 5-MTHF. Below are some selected studies.
Folic Acid Versus 5-MTHF
A systematic review found 23 potential animal and human studies (4 animals and 19 humans) that looked at the different supplementation forms for folate (folic acid, folinic acid, and 5-MTHF). Only 3 of 12 studies comparing folic acid to 5-MTHF demonstrated a statistically significant difference between the two, with 5-MTHF more effective than folic acid. Ultimately, they pointed to the limitations of the study as requiring more research. Let’s look a bit closer at some individual studies, both included in the review and not.
Increased Serum and Plasma Folate Levels
Many of the studies evaluating the two supplemental forms looked at increased blood and/or plasma levels of folate. For example, a study on Malaysian women compared 2.27 umol folic acid, 2.27 umol of 5MTHF, and a placebo for 12 weeks. Both folate supplements led to higher red blood cell and plasma folate levels and lower homocysteine levels than the placebo group. However, the 5MTHF had higher levels than the folic acid group.
Another study found that 7.5 mg per day of 5-MTHF compared to folic acid led to 23 to 55 percent higher serum total folate. The 5-MTHF increased serum folate levels to the targeted level for the study more quickly. However, after 12 days, the results became more uniform between the two groups. A similar trend was found in another double-blind, randomized, placebo-controlled trial comparing 400 ug of folic acid, 416 ug of 5-MTHF, and a placebo for 24 weeks. There was a significantly higher increase in red blood cell folate in the 5-MTHF group.
Likewise, other researchers reported that 16 weeks of 416 ug of 5-MTHF led to higher red blood cell folate but not plasma folate concentration compared to 400 ug of folic acid in lactating women who had consumed a prenatal vitamin with 1000 ug/d of folic acid during pregnancy. There was also less unmetabolized folic acid, with the group taking the 5-MTHF having 24 nmol/L compared to 46 nmol/L in the folic acid group. A pharmacokinetic study found higher bioavailability for 5-MTHF compared to folic acid regardless of the MTHFR genotype.
Impact of 5-MTHF on Homocysteine Levels
Another common area of research evaluating the two forms of folate look at the impact on homocysteine levels. One randomized, double-blind, controlled trial compared getting folate from food, folic acid supplementation, and 5-MTHF supplementation, all with daily values of 200 ug of folate, and a placebo control group to see the impact on those with moderate hyperhomocysteinemia. All three led to a similar reduction in homocysteine levels (20.1 percent for diet, 19.4 percent for 5-MTHF, and 21.9 percent for folic acid). The placebo group experienced an increase in homocysteine levels by 4.8 percent.
Comparing 5-MTHF with folic acid and control on homocysteine levels in liver transplant patients found only the 5-MTHF group experienced a significant decrease (34 percent versus 24 percent in the folic acid group). They took either 1 mg 5-MTHF, 1 mg folic acid, or placebo for 8 weeks. Additionally, the homocysteine levels remained decreased a few weeks after ending the supplementation in the 5-MTHF group. Another study found that in healthy females, 24 weeks of supplementation of 400 ug folic acid, 416 ug 5-MTHF, and 208 ug 5-MTHF led to similar reductions in homocysteine levels to a placebo. However, the 5-MTHF groups did have a slightly larger reduction (19 percent for both 5-MTHF groups compared to 15 percent in the folic acid group, calculated relative to the placebo).
Genetic SNPs Impacting MTHFR
Many studies also examine whether 5-MTHF works more efficiently in those with genetic SNPs, especially impacting MTHFR. Mechanistic studies have found that cells with reduced MTHFR activity respond better with 5-MTHF than folic acid. In one study, both were effective, but 5-MTHF was 14-20 percent higher, depending on the dose, while the cells without the genetic mutation had no difference between folic acid and 5-MTHF. This study also found that 5-MTHF supplementation led to statistically significantly higher intracellular folate concentrations than folic acid, while those without the mutation did not. Other mechanistic studies have also noticed a potential inhibitory effect of folic acid on the uptake of 5MTHF.
In women with the CT or CC genotype, folic acid supplementation worked better to decrease homocysteine levels than 5-MTHF. Another randomized, crossover study on women, comparing homozygous with the 677C to T MTHFR mutation and homozygous wild type, used a single dose of 400 ug of folic acid and 5-MTHF. The increase in plasma folate was higher for both groups using the 5-MTHF supplementation.
One randomized, double-blind, control trial compared taking 1 mg folic acid with 1 mg 5-MTHF in women with recurrent miscarriages and found no benefit with either supplementation in those who had any of the MTHFR polymorphisms. As a secondary measure, the group did have significantly higher serum folate levels than those on the folic acid. Both had significantly lower homocysteine levels that did not differ significantly between the two groups.
A few studies investigated the two forms of supplementation in outcomes beyond folate and homocysteine levels. One study found it more likely for 5-MTHF to transfer to the fetus than folic acid (based in part on cord levels of 5-MTHF levels much higher than maternal levels while there was no significant difference in folic acid levels), and it was also associated with lower levels of homocysteine.
Using 5-MTHF and folic acid in infant formula, researchers reported no significant difference between the two in weight gain and head circumference. However, the infants consuming the 5-MTHF formula had lower levels of unmetabolized folic acid equivalent to breastfed infants and higher red cell folate.
A randomized, controlled trial looked at using 400 ug of folic acid, 5-MTHF, or placebo for 16 weeks on patients with peripheral arterial disease. Both forms of folate supplementation led to a significant reduction of plasma homocysteine levels. The 5-MTHF group had a significant decrease in brachial-knee PWV, while the folic acid had a trend, and both reached significance when comparing the patient’s bk-PWV at the end of treatment with their own baseline levels. There was no significant difference in the efficacy between the two forms of folate.
One study evaluated 50 mg I.V. 5-MTHF and 5 mg/day oral folic acid, along with B6 and B12 supplementation, in patients undergoing hemodialysis. The I.V. 5-MTHF experienced improved survival rates independent of homocysteine levels, which were similar in both groups. However, the reduction was greater for the 5-MTHF group in the first 6 months. They found the difference likely due to the inflammatory state, as at 24 and 55 months, the 5-MTHF group experienced a much lower CRP value (9.0 compared to 2.1 at 24 months, and 8.1 compared to 18.4 at 55 months), and CRP levels were a predictive risk factor for death.
While it is still early in the research, there are some promising results with 5-MTHF. Many studies did find that it worked better in increasing folate levels and lowering homocysteine levels, although not all studies demonstrated a statistically significant difference. More research is needed to understand the impact of unmetabolized folic acid fully and whether those potential problems are avoided by 5-MTHF supplementation instead. Additionally, more comparison studies are necessary that look beyond the increase in serum and/or plasma folate levels and homocysteine levels to determine if there are specific conditions for which one form of folate may be superior to another.
For now, if you feel you need additional folate and wish to supplement, talk with your doctor, nutritionist, dietician, or another member of your healthcare team to determine the right form and dosage for your situation.