Vitamin B12 (cobalamin) for fertility

On this page

1. What is vitamin B12?
2. Function and how it works
3. Fertility benefits
4. Recommended daily dose
5. Food sources
6. Cautions and contraindications
7. My Fertility Guide
8. Related pages

1. What is vitamin B12?

Vitamin B12 (cobalamin) is a water-soluble B vitamin essential for cell division, DNA synthesis, red blood cell formation and nervous system function. Unlike most water-soluble vitamins, B12 can be stored in the liver for several years — but vegetarians, and especially vegans, are at high risk of deficiency because B12 is found almost exclusively in animal-source foods.

Reference ranges and recommended intakes vary from country to country — always interpret guidance against the recommendations of your own healthcare authority.

2. Function and how it works

Vitamin B12 works closely with folic acid in fertility:

1. Cell division. Together with folic acid, B12 is essential when new genetic material is made during cell division, helping to prevent birth defects such as spina bifida.
2. DNA synthesis. The active form (methylcobalamin) provides methyl groups for DNA synthesis and gene regulation.
3. Red blood cell formation. B12 deficiency causes a specific type of anaemia (megaloblastic) that contributes to fatigue and infertility.
4. Sperm quality. Research has shown that B12 supplementation benefits men with a low sperm count and improves sperm motility.
5. Homocysteine regulation. B12 (with folic acid and B6) keeps homocysteine levels in check.

3. Fertility benefits

For women, B12 works together with folic acid to support cell division during early pregnancy and prevent birth defects. For men, B12 supplementation has been shown to improve sperm count and motility. Vegetarians and vegans must supplement B12 to ensure adequate levels — deficiency is one of the most common causes of unexplained fertility difficulties in plant-based diets.

4. Recommended daily dose

I recommend a daily dose of 3–5 mcg of vitamin B12, typically obtained as part of a good-quality prenatal or B-complex supplement. Higher doses (1,000 mcg or more) are sometimes used to correct documented deficiency, particularly in vegans. The methylcobalamin form is preferable to cyanocobalamin for most people.

5. Food sources

Vitamin B12 is found almost exclusively in animal-source foods:

1. Oily fish (sardines, salmon, mackerel)
2. Red meat (beef, lamb)
3. White fish (cod, haddock)
4. Eggs
5. Dairy products (milk, cheese, yoghurt)
6. Fortified plant milks and nutritional yeast (for vegans)

Plant foods generally do not contain B12. Vegans should supplement and may benefit from periodic blood testing of B12 status.

6. Cautions and contraindications

1. B12 is generally very safe; toxicity from oral supplementation is extremely rare.
2. Vegetarians and vegans should test their B12 status periodically and supplement as needed.
3. Some medications (including metformin and proton pump inhibitors) reduce B12 absorption.
4. Always consult with a fertility specialist or your doctor before starting any new supplement regime.

7. My Fertility Guide

8. Related pages

• Fertility supplements directory
• Folic acid (vitamin B9)
• Vitamin B6 (pyridoxine)
• Iron
• Bee pollen
• Low sperm count