According to the National Institute for Health and Clinical Excellence, one in seven couples in the UK have problems conceiving. Most couples (about 80%) who are trying to get pregnant do so within a year and about 90% succeed in 2 years. About 50% of fertility problems are due to problems with the man, while at least 20% of cases of infertility have no known reason.
Scientists from the University of Stockholm have already shown that higher vitamin D levels in men are associated (association is not causation) with healthier sperm, faster sperm, sperm better able to penetrate the female egg. Randomized controlled trials of men, women, and couples are underway to see if vitamin D supplements help couples conceive, but the results will not be available for years.
A recent basic science paper by Drs. Martin Bloomberg Jensen and Sten Dissing of the University of Copenhagen further explain how vitamin D is involved in fertility.
In order to understand vitamin D’s role in infertility, you have to know something about vitamin D’s other mechanism or action, its “non-genomic” or “non-gene” action. Besides working as a key that switches genes on and off, vitamin D has another mechanism of action, one seldom studied. This one occurs in the cell wall, not the nucleus, seems to require boron, and works in a matter of minutes. Human sperm are ideal candidates to study this mechanism as they rely on this “non-genomic” mechanism.
The authors state, “Both animal and human studies have shown that vitamin D serum levels and local vitamin D metabolism in the male reproductive tract are important for male reproductive health.” Then the authors went about determining in their study that vitamin D, using this non-genomic action, increases calcium, first inside the necks and then the heads of the sperm, a quality the sperm need to have to do their job in penetrating the egg.
Additionally, the authors found that the sperm, on their travels, require vitamin D to be present in the women’s reproductive tract. “We suggest that 1,25(OH)₂D is present in sufficient quantity in the female reproductive tract to increase sperm motility and induce the acrosome reaction (penetration of the egg’s tough shell), thereby facilitating penetration of the surrounding cumulous (surrounding) cells and fertilization of the oocyte.”
This paper adds to the growing list of papers indicating vitamin D is probably crucial for human reproduction. There are multiple causes of infertility that vitamin D will probably not help, the most common being past infections, but with research to date, there is little reason not to be sufficient in vitamin D for reproduction. Fortunately, fertility doctors can do so many different things these days, that most couples will walk away with a baby.
It is important to stress that this is both the man’s and the woman’s responsibility to be sufficient in vitamin D before conception (we recommend 5,000 IU/day), and it is their responsibility to see that their child is not vitamin D deficient as he/she grows. This requires the mother to take at least 5,000 IU/day when breastfeeding and then giving increasing doses of vitamin D to the child after weaning, as the child grows and grows.