B12 Deficiency and Fertility: Cyanocobalamin vs. Methylcobalamin

Jul 05, 2024

B12 Deficiency and Fertility: Cyanocobalamin vs. Methylcobalamin

Vitamin B12, also known as cobalamin, is like a multitasking superhero for your body. It's essential for making DNA, keeping your nerves in top shape, and producing red blood cells. But did you know it also plays a vital role in fertility for both men and women? 

Low B12 levels can throw a wrench in your body's methylation process, leading to higher levels of homocysteine, which studies have shown is linked to miscarriage and recurrent pregnancy loss.

For women, a B12 deficiency can disrupt ovulation and cause chronic implantation problems, making it harder to conceive.

Furthermore,  emerging research indicates that B12 deficiency also affects male fertility. Vitamin B12 is critical for enhancing sperm motility, improving sperm concentration, and protecting against DNA damage in sperm cells, all of which are essential for healthy sperm quality.

Vitamin B12 comes in four forms: Adenosylcobalamin, Cyanocobalamin, Hydroxocobalamin, and Methylcobalamin. But let's keep it simple and focus on the two you’ll most often find in supplements: cyanocobalamin and methylcobalamin. 

  • Cyanocobalamin: Cyanocobalamin is a cyanide-based form of B12 that is widely available and less expensive to produce. It's commonly used in supplements and fortified foods because of its stability and cost-effectiveness. Once ingested, your body transforms cyanocobalamin into the active forms of Vitamin B12: methylcobalamin and adenosylcobalamin. However, it's important to note that cyanocobalamin might not be the best choice for everyone. 

  • While the small amount of cyanide released during cyanocobalamin conversion is generally considered safe for most people, those with suboptimal health or compromised kidney function might not convert it as effectively. Furthermore, people with kidney problems may have difficulty processing cyanocobalamin efficiently or removing cyanide from their bodies. In such cases, high doses of cyanocobalamin could potentially build up cyanide, worsening their condition and increasing toxicity.

  • Methylcobalamin: Methylcobalamin is one of the active forms of Vitamin B12 that the body can readily use. It occurs naturally in food sources like fish, meat, eggs, and dairy products. One of its key benefits is that it contains no cyanide, which, while not harmful at low levels, may affect retention in some individuals.
  • Adenosylcobalamin, just like methylcobalamin, is crucial for many aspects of your health. It helps your body break down fats and amino acids, and it's important for making myelin, which protects your nerves. Methylcobalamin and adenosylcobalamin can interconvert, so if you take methylcobalamin, you also get adenosylcobalamin.

    So, which forms of B12 should you go for?

    Well, while Cyanocobalamin is okay for absorption, studies show Methylcobalamin is better retained and lasts longer. If your health isn't optimal, it can also be more challenging for the body to convert Cyanocobalamin into its active forms of vitamin B12.

    That's why natural forms like Methylcobalamin and Adenosylcobalamin are a better bet—they're more effective and safer. This is the reason our Fab Prenatal is packed with Methylcobalamin and Adenosylcobalamin, ensuring both you and your little one get all the health benefits.

    Learn more about our Fab Prenatal and other foundational supplements to support fertility with our Fab For Life Naturals Fertility Collection. Use FAB15 to save 15%

    Bennett M. Vitamin B12 deficiency, infertility and recurrent fetal loss. J Reprod Med. 2001 Mar;46(3):209-12. PMID: 11304860.


    Banihani SA. Vitamin B12 and Semen Quality. Biomolecules. 2017 Jun 9;7(2):42. doi: 10.3390/biom7020042. PMID: 28598359; PMCID: PMC5485731.

    Kelly, N.D., G. (1997). The Coenzyme Forms of Vitamin B12: Toward an Understanding of their Therapeutic Potential. Retrieved from


    Paul C, Brady DM. Comparative Bioavailability and Utilization of Particular Forms of B12 Supplements With Potential to Mitigate B12-related Genetic Polymorphisms. Integr Med (Encinitas). 2017 Feb;16(1):42-49. PMID: 28223907; PMCID: PMC5312744.