The human reproductive system consists of many cogs and gears that must run smoothly in order for reproductive success. While many factors contribute to impaired fertility, in women, regular menstrual cycle are associated with reproductive success. In fact, irregular menstrual cycles have been linked to absence of ovulation and delayed time to pregnancy.
When I took a moment with Dr. John Cannell to discuss this paper, he reflected upon his time as a general practitioner in the 1980’s,
“…a surprisingly high number of women would come to me asking why they couldn’t get pregnant. I told them, before I referred them to a gynecologist, that many couples (about 20%) trying to conceive, remain childless after trying for a year. But, many of those couples would get pregnant during their second year of trying. I knew the most common cause of female infertility is ovulatory problems which generally manifest themselves by sparse or absent, as well as excessively long, menstrual cycles.”
Anovulation, or the absence of ovulation, is common, affecting between 6-15% of women of reproductive age. Though not always an indicator of infertility, this is a very common sign that some part of this complex system is not working as it should. Additionally, individuals experiencing anovulation are at a higher risk of complications, should pregnancy occur.
Modern research has identified vitamin D receptors in the uterus, ovaries and placenta, indicating some kind of role for vitamin D in the reproductive system. Additionally, multiple studies have discovered a relationship between vitamin D and reproductive health, including evidence supporting an effect of vitamin D status on women’s menstrual cycles. However, limited research has evaluated the effect of vitamin D status on the length of menstrual cycles, therefore, a group of researchers recently explored this relationship.
Researchers recently evaluated the effect of vitamin D status on menstrual cycle length in a group of women attempting to become pregnant. The women were between the ages of 30-44 and had been attempting pregnancy for at least three months. Individuals were excluded if they had a past medical history of infertility, polycystic ovarian syndrome (PCOS), a partner with infertility, endometriosis or were currently breastfeeding.
Prior to this study, the women filled out a questionnaire covering demographic data, history of contraceptive use and reproductive history. Additionally, the women were asked to keep a daily diary of their menstrual periods and results of ovulation and pregnancy tests for up to four months, followed by a monthly diary until pregnancy or 12 months passed. All participants were required to schedule a lab visit at the beginning of their menstrual period (at day two, three or four) in order to have a serum 25(OH)D status measured.
This is what the researchers found:
- A total of 446 women provided at least one entry into their daily diary, with a total of 1,277 menstrual cycles recorded from these women.
- Average vitamin D status was 34 ng/ml (85 nmol/l).
- Menstrual cycle length ranged from 19 to 68 days.
- For each 10 ng/ml (25 nmol/l) decrease in vitamin D levels was associated with a 30% increased odds of longer menstrual cycle length.
- Vitamin D levels below 20 ng/ml (50 nmol/l) were associated with a nearly three times increased odds of longer menstrual cycles compared to individuals with levels above 40 ng/ml (100 nmol/l) (OR: 2.8; CI: 1.0, 7.5).
- Insufficient vitamin D levels (20-30 ng/ml; 50-75 nmol/l) were associated with nearly a two times increased odds of longer menstrual cycles compared to those with levels above 40 ng/ml (100 nmol/l).
The researchers concluded:
“In conclusion, these findings suggest that vitamin D status influences menstrual cycle length through an association with longer follicular phase (delayed ovulation).”
It is important to address limitations of this study, as this should be taken into consideration when interpreting the findings. First, many of the women were not vitamin D deficient at the beginning of the study, which could have affected the analysis of the collected data. Additionally, while a similar study conducted in African-American women resulted in data consistent with this study, the majority of the participants in this study were affluent, white women. This limits the generalizability of these findings.
Despite these weaknesses, there is a growing body of evidence supporting the role of vitamin D in menstrual regularity and reproductive health. Have you had an experience with vitamin D and reproductive health? We are always looking for stories of inspiration to share with the community. Please reach out to us at [email protected] to share your story.
Peterson, R. & Cannell, JJ. Menstrual cycle length is increased in women with low vitamin D levels compared to women with higher levels. The Vitamin D Council Blog & Newsletter, 2/2018.