A recent study published by the journal Fertility and Sterility found that low vitamin D status is related to long menstrual cycles in African American women.
Women around the ages of 15-44 years will usually experience menstrual periods every 28 days, with each cycle lasting for an average of 3-7 days. The regularity of these menstrual cycles is a sign of fertility and a properly functioning reproductive system.
Abnormal cycles may indicate an underlying issue or change. In fact, abnormal cycles may be a sign of pregnancy, hormonal imbalances, infection and tumors in the reproductive tract; though, an underlying physical component is not always the root of the problem.
Past research has found a link between vitamin D and several reproductive disorders, including reduced fertility, uterine fibroids and polycystic ovary syndrome (PCOS). Since vitamin D receptors are expressed in the ovaries, placenta and uterus, researchers theorize that low vitamin D status may contribute to the development of a dysfunctional reproductive system.
However, minimal research evaluating the relationship between vitamin D and menstrual cycle function exists. In the only study that has looked into this matter to date, researchers found that vitamin D was related to menstrual cycle irregularity in women of late reproductive age (35-44 years).
Therefore, researchers recently examined the relationship between vitamin D and menstrual cycle length in African American women between the ages of peak reproductive age (23—34 years) from the Detroit area. This population is of particular interest due to the high prevalence of vitamin D deficiency. Individuals were excluded from the study if they were taking cycle regulating medications for the past year.
A total of 1,102 participants were included in the study. They had their 25(OH)D levels measured and provided a 12-month gynecologic history based off four independent categories describing cycle duration: normal (27-34 days), short (<27 days), long (>34 days) or irregular (too irregular to estimate).
Did the researchers find a relationship between vitamin D status and menstrual cycle length? Here is what they found:
- The median vitamin D status was 14.7 ng/ml.
- Only 24% of the participants were vitamin D sufficient (>20 ng/ml).
- The highest vitamin D level of the 1,102 participants was 22.7 ng/ml.
- A vitamin D status of >20 ng/ml was associated with a 50% reduced odds of having long menstrual cycles.
- Vitamin D status was not related to the presence of short or irregular menstrual cycles.
The researchers concluded,
“These findings suggest that vitamin D status may influence the menstrual cycle and play a role in ovarian function.”
According to the Vitamin D Council’s standards, none of the study participants were considered vitamin D sufficient (levels between 40-80 ng/ml). Additionally, with the single cut off point of 20 ng/ml, one may question if more clinically relevant findings would be present if the researchers utilized a more comprehensive range of vitamin D status classifications. However, the fact that the researchers were able to find a significant association between vitamin D deficiency and long menstrual cycles shows that further research on this relationship is warranted.
The researchers call for prospective studies of vitamin D and menstrual cycle length to further validate these findings.
Sturges, M. & Cannell, JJ. Vitamin D deficiency associated with long menstrual cycles in African American women. The Vitamin D Council Blog & Newsletter, 2016.