Hidden Cancer Dangers: Synthetic Folic Acid


Written by Keith Bishop, Clinical Nutritionist, BSc Pharmacy, Author
March 16, 2024

In the quest for optimal health, many turn to supplements, like multiple vitamins with folic acid. But what if the very supplement you’re taking for better health could have hidden cancer concerns?

I review blood tests each day in my clinical nutrition appointments. Since 1999 I have seen fewer than six people with a folate level in the normal range and only one person with a low folate level. That means I’ve seen over 20,000 people with high blood levels of folate. Could this be part of the reason why we have such high rates of cancer?

The Concerns Around Synthetic Folic Acid

Synthetic folic acid is the man-made version of the vitamin folate, a crucial nutrient for many processes in our body including DNA synthesis, cell division and repair, and neurotransmitter receptor function. Folate, also known as vitamin B9, is essential for various bodily functions, including cell division and proper fetal brain and nervous system development. That’s part of the concern – cell division.

Recent studies have highlighted a potential link between high levels of synthetic folic acid and an increased risk of certain cancers. This is in part attributed to the metabolite N-nitroso-folic acid, which forms in the manufacturing process of making a supplement with folic acid. The concern grows with higher doses and blood levels of this compound.[i]

While naturally occurring, folate is beneficial and even necessary, its synthetic counterpart is raising eyebrows in the scientific community. Folate's impact on cancer risks is a subject of intense research with conflicting findings. I’m giving you a summary of the relationship between folic acid, cancer risk, and optimal folate levels.

Low Folate and Cancer Concerns

Several medical studies have linked low folate status to an increased risk of several cancers. Folate deficiency disrupts DNA repair mechanisms that may contribute to the development of cancer. Low folate levels have been associated with:[ii] [iii]

  • Colorectal cancer
  • Acute lymphoblastic leukemia (ALL)
  • acute myeloid leukemia (AML)
  • Cervical cancer
  • Head and neck squamous cell carcinoma
  • Lung cancer
  • Breast cancer
  • Ovarian cancer

High Folate and Cancer Concerns

On the other hand medical studies have linked elevated folic acid doses and blood levels with an increased risk of:[iv] [v] [vi] [vii] [viii]

  • Prostate cancer
  • Lung cancer in people who smoke
  • Breast cancer risk increased significantly with daily folate intake of >400 mcg
  • Ovarian cancer
  • Endometrial cancer

800mcg daily folic acid plus vitamin B12 was associated with an elevated risk of cancer and all causes of death.

Learn about other vitamins and minerals that can cause cancer. 

The Fine Balance: Optimal Folate Levels

Determining the ideal folate levels for cancer prevention remains challenging. Here are some key considerations:[ix]

Recommended Dietary Allowance (RDA): The RDA for adults in the USA is 400 micrograms (mcg) of dietary folate equivalents (DFE) per day. This includes dietary folate, folic acid from food, and supplemental folic acid.

Upper Limit: The upper limit for folate intake is 1,000 mcg/day, as higher doses may mask vitamin B12 deficiency.

Gene Interactions: Genetic variations (such as MTHFR and SHMT polymorphisms) may impact individual responses to folate intake. A homocysteine blood test is a functional evaluation of how your body is obtaining and using folic acid and folate. A homocysteine blood level of less than 10 is ideal.

Methylated Folate as an Alternative

Methylated folate is the bioavailable form of folate, meaning it's more readily absorbed and utilized by the body. This form particularly benefits those with MTHFR gene mutations, affecting up to 60% of the population.

Unlike synthetic folic acid, methylated folate doesn't seem to have the same association with increased cancer risk, making it a safer alternative for those looking to supplement.

Importance of Folate Blood Testing          

Knowing your folate levels can be a key factor in personalized nutrition and health. Too little folate can lead to health issues, but too much, especially in the form of synthetic folic acid, can also pose risks.

For those interested in monitoring their folate levels, your healthcare provider and services like https://www.ultalabtests.com/partners/prevailovercancer/  offer convenient testing options. Remember, it's essential to discuss your results and any supplement changes with your healthcare provider.

Natural Sources of Folate

While supplements can be beneficial, obtaining nutrients from your diet ensures you're getting them in their most natural form.

Incorporating folate-rich foods into your diet, such as legumes (beans and lentils), spinach, kale, arugula, and asparagus can help you maintain optimal levels without the need for synthetic supplements.

In your journey towards health, knowledge is power. By choosing the right form of folate and understanding the potential benefits and risks we can make informed decisions that support our health and well-being.

Folate Cancer Summary

My goal for myself and my clients is to avoid synthetic folic acid-enriched foods and supplements, consume plenty of anticancer folate-rich foods, take a moderate amount of methyl-folate (<400 mcg), and monitor folate and homocysteine blood levels.

Get the rest of the story. Go to my blog and learning center and download my guide Vitamins and Minerals that Cause Cancer.


This information is for educational purposes. As with any information on the internet and social media, you should consult with your healthcare providers before making changes in your treatment program.

These statements have not been evaluated by the Food and Drug Administration. Supplements are not intended to diagnose, treat, cure, or prevent any disease.

Reference Sources Include

[i] Zeng Y, Teo J, Lim JQ, et al. Determination of N-nitroso folic acid in folic acid and multivitamin supplements by LC-MS/MS. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2024;41(1):1-8. doi:10.1080/19440049.2023.2292603 https://www.tandfonline.com/doi/full/10.1080/19440049.2023.2292603

[ii] Cantarella CD, Ragusa D, Giammanco M, Tosi S. Folate deficiency as predisposing factor for childhood leukaemia: a review of the literature. Genes Nutr. 2017;12:14. Published 2017 Jun 2. doi:10.1186/s12263-017-0560-8

[iii] Arthur RS, Kirsh VA, Rohan TE. Dietary B-Vitamin Intake and Risk of Breast, Endometrial, Ovarian and Colorectal Cancer among Canadians. Nutr Cancer. 2019;71(7):1067-1077. doi:10.1080/01635581.2019.1597904 https://www.tandfonline.com/doi/full/10.1080/01635581.2019.1597904

[iv] Pieroth, R., Paver, S., Day, S., & Lammersfeld, C. (2018). Folate and Its Impact on Cancer Risk. Current Nutrition Reports, 7(3), 70–84.

[v] Shulpekova Y, Nechaev V, Kardasheva S, et al. The Concept of Folic Acid in Health and Disease. Molecules 2021; 26: 3731

[vi] Stanisławska-Sachadyn A, Borzyszkowska J, Krzemiński M, et al. Folate/homocysteine metabolism and lung cancer risk among smokers. PLoS One. 2019;14(4):e0214462. Published 2019 Apr 2. doi:10.1371/journal.pone.0214462 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6445430/

[vii] Chen P., Hu P., Li M., Li X., Guo H., Li J., Chu R., Zhang W., Wang H. Folate intake and MTHFR polymorphism C677T is not associated with ovarian cancer risk: Evidence from the meta-analysis. Mol. Biol. Rep. 2013;40:6547–6560. doi: 10.1007/s11033-013-2686-0.

[viii] Ebbing M, Bønaa KH, Nygård O, et al. Cancer incidence and mortality after treatment with folic acid and vitamin B12. JAMA. 2009;302(19):2119-2126. doi:10.1001/jama.2009.1622 https://jamanetwork.com/journals/jama/fullarticle/184898

[ix] Pieroth R, Paver S, Day S, Lammersfeld C. Folate and Its Impact on Cancer Risk. Curr Nutr Rep. 2018;7(3):70-84. doi:10.1007/s13668-018-0237-y


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