There is a lot of talk around vitamin D and pregnancy rates and outcomes but what exactly is known about the relationship between vitamin D and assisted reproduction? Here we look at the studies that have evaluated the effect.
Vitamin D Modulatory Process
It is well known that vitamin D receptors are distributed across reproductive systems including ovaries, uterus and endometrium. Furthermore it is known that vitamin D stimulates egg production, most follicular maturation and regulates successful implantation, and it may be involved in polycystic ovarian syndrome.
Vitamin D and Reproductive Outcomes
In animals there seems to be a strong association between reproductive outcomes with vitamin D. Women participating in the NHS 2 study, Nurse health study number 2, vitamin D was unrelated to infertility. Similarly it was not associated with either/or probability of conception in healthy Danish women or conception in less than one year among Italian women undergoing routine aneuploidy screening. Furthermore meta-analysis of 10630 pregnant women revealed no association between low vitamin D levels and miscarriage rates, though extremely low levels of less than 29 gram per ml were associated with increased risk of miscarriages in a small number of women.
Vitamin D and Assisted Conception Outcomes
Though vitamin D may give a positive benefit for reproductive outcomes, vitamin D on ART outcomes are inconsistent. In a large meta-analysis of 11 studies of women undergoing ART, it was found that women deficient in vitamin D levels had a higher probability of live birth, but no association with vitamin D with probability of miscarriage was noted. Similarly another study found in PCOS patients that vitamin D of great than 30 nanogram per ml was associated with lower live birth rates. This proved other studies which showed there was no association between vitamin D concentrations and the assisted conception outcomes. Furthermore two further randomised control trials did not improve pregnancy outcomes. Neither giving 50 thousand international units of vitamin D for six to eight weeks for deficient women, nor administering a megadose of 300 thousand in women with PCOS improves outcome.
In summary we could suggest that vitamin D can affect reproduction, though at present evidence is limited. Extremely low vitamin D levels are related to worse outcomes in ART.