Short answer: B12 is needed for blood formation and the nervous system. Preventing and treating deficiency is important, but extra B12 has not been shown to increase fertility in everyone. A vegan diet requires a reliable source of B12, and reduced absorption can cause deficiency even in those who eat animal-based foods.
What does vitamin B12 do in the body?
Vitamin B12 (cobalamin) is needed for the formation of red blood cells, for DNA synthesis, and for the function of the nervous system. Together with folate, B12 participates in the metabolism of the amino acid homocysteine – a process that is central when cells divide rapidly, for example during the formation of reproductive cells and early in pregnancy. According to the Swedish Food Agency, B12 is found almost exclusively in animal-based foods such as meat, fish, seafood, eggs, and dairy products, and the recommended intake for adults is around 4 micrograms per day.
B12 and female fertility
Studies that have compiled the role of nutrients in reduced fertility have noted that low levels of B12 may occur more often in women with fertility difficulties, and that B12 together with folate may be important for egg quality and early embryo development. It should be emphasized that much of this is based on observational studies with limited data – they show associations, not that B12 supplements themselves improve the chance of becoming pregnant. With a varied diet, deficiency is uncommon.
B12 and male fertility
In men too, research has examined the connection between B12, folate, and sperm quality. Some studies suggest that good B12 status may be associated with better sperm parameters, but the results are mixed and the evidence is not sufficient to draw certain conclusions. As part of a nutritious diet and healthy lifestyle, it is reasonable to ensure that B12 intake is sufficient, but B12 should not be considered a treatment for reduced sperm quality.
Deficiency, risk groups, and pregnancy
B12 deficiency is more common in people who eat little or no animal-based foods, with certain gastrointestinal conditions, and with increasing age. During pregnancy, measured B12 levels may drop without it alone indicating deficiency. Symptoms of deficiency can be fatigue, tingling in the hands and feet, and cognitive sluggishness. The Swedish Food Agency recommends that vegans – and vegetarians who eat very few eggs and dairy products – take B12 supplements. If you suspect a deficiency, you should get tested through healthcare rather than guessing.
Do you need supplements?
For those who eat a mixed diet with meat, fish, eggs, or dairy products, B12 needs are usually met by food. Supplements are particularly relevant with a vegan or strongly plant-based diet, and may be considered in consultation with healthcare providers if a deficiency or risk factors are identified. A supplement does not replace an investigation – if you have been trying to get pregnant for a longer period, it is worth seeking medical care for a comprehensive assessment.
Frequently asked questions
Can B12 supplements help me get pregnant?
There is no strong evidence that B12 supplements increase the chance of becoming pregnant in people without a deficiency. Good B12 status is part of overall nutritional status, but supplements are primarily justified in cases of low or insufficient intake, for example with a vegan diet.
How do I get enough B12?
B12 is found primarily in animal-based foods such as meat, fish, seafood, eggs, and dairy products. If you eat plant-based, fortified products and supplements may be needed to meet the requirement.
How do I know if I have a deficiency?
Deficiency is identified through blood tests via healthcare, sometimes supplemented with markers such as homocysteine and methylmalonic acid. Do not guess based on symptoms – let healthcare professionals assess.
This text is general information and not medical advice. It does not replace an individual assessment. Consult healthcare providers if you have questions about your fertility, suspect a nutrient deficiency, or are considering dietary supplements, especially if you are pregnant or breastfeeding.
Problems with absorption can cause B12 deficiency even with a mixed diet. A low test result during pregnancy needs to be interpreted in context and is not a diagnosis on its own.