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Male Infertility and the Role of Vitamin B-12

By Owen Bond

It is estimated that up to 25 percent of couples in the United States have trouble conceiving. Male infertility is a prominent cause and involves reduced sperm production or sperm mobility. Sometimes medical intervention is necessary, but many couples explore herbal and vitamin supplements in efforts to enhance fertility. Vitamin B-12 supplements may improve sperm counts and sperm mobility, although as of 2011, further human studies are needed to determine definitive benefits.


Infertility is medically defined as the failure of a couple to become pregnant after one year of regular, unprotected intercourse. Low sperm count in the semen, decreased sperm mobility or abnormal sperm shape is responsible for about 40 percent of infertility in these couples, according to “Harrison's Principles of Internal Medicine.” There are numerous possible causes for male infertility, some of which may respond to herbs, minerals or vitamins. If possible, the specific cause of male infertility should be diagnosed by your doctor before any supplements are considered.

Vitamin B-12

Vitamin B-12 is a large, complex molecule primarily associated with higher brain functions, red blood cell production and cellular metabolism. B-12, along with folic acid, is also important for the formation, maturation and duplicating of DNA, which is the genetic information within all cells, including sperm. B-12 is produced in small amounts in your intestines by friendly bacteria, widely present in animal-based protein and green leafy vegetables, or available as a synthetic supplement, known as cyanocobalamin. Supplemental B-12 is usually taken as a sublingual tablet or injected into the bloodstream. According to “Vitamins: Fundamental Aspects in Nutrition and Health,” B-12 deficiency often takes months or years to manifest symptoms, may be more common in the U.S. than previously thought and can lead to dementia-like symptoms, anemia, sluggish metabolism and reduced sperm counts.

B-12 and Male Infertility

Vitamin B-12 supplementation via injection and its effect on sperm counts has been investigated since the 1970s. According to “Nutritional Sciences,” studies have shown that men who have reduced sperm counts because of a B-12 deficiency benefit from mega-dosing oral B-12 supplements, up to 1,500mcg, or receiving an injection. However, in men who have low sperm counts but are not deficient in B-12, only about 40 percent on average showed a significant improvement and a small percentage actually got worse. B-12 deficiency is thought to cause genetic damage in sperm cells, leading to infertility. Why B-12 supplementation can improve sperm counts in some men who do not have a deficiency may be related to increased energy metabolism and having more resources to produce sperm, or higher oxygenation due to the boost in red blood cell production. As of 2011, more research is needed to clarify the relationship, although there is essentially no risk in mega-dosing B-12 to see if it impacts sperm counts, which is why some fertility experts recommend it.

Other Advice to Improve Male Fertility

In addition to B-12 supplements, other vitamins, minerals and amino acids have been linked to increasing sperm counts, motility or quality including vitamin C, zinc, selenium, arginine and L-carnitine, as cited in “Biochemical, Physiological and Molecular Aspects of Human Nutrition.” Dietary changes that may be helpful include avoiding alcohol, quitting smoking and eating organically grown foods.

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