About a month ago, we covered a study from the National Institutes of Health which found that vitamin D deficiency was linked to irregular menstrual cycles. However, the potential mechanisms of this relationship was left unexplained.
The authors reported prior cross-sectional studies have shown that lower vitamin D levels are associated with multiple gynecological problems, such as premenstrual syndrome, uterine fibroids, painful periods and early menopause.
The researchers suggested a possible mechanism of action for vitamin D’s effects on gynecological problems. They pointed out that vitamin D influences the gene encoding for anti-Müllerian hormone (AMH), a glycoprotein with multiple effects in both males and females. The gene coding for AMH contains a domain for the vitamin D response element, suggesting that vitamin D can regulate AMH expression. AMH is associated with the number of eggs females have left in their ovaries so AMH declines to undetectable blood levels at menopause. AMH also regulates egg development, which provides a mechanism for vitamin D to influence ovarian function and menstrual cycle regularity.
The investigators obtained 25(OH)D levels on 636 women from Washington D.C., aged 30 to 49, and asked them about menstrual cycle length: short, long, normal or irregular. Forty-eight women (8%) reported that their cycle length was “ too irregular to estimate,” and were classified as having irregular cycles; 29% reported short cycles (<25 days) and 11% reported long cycles (>32 days).
The mean 25(OH)D of the 636 women was 14 ng/ml and 76% of the women had vitamin D levels below 20 ng/ml. Vitamin D levels were not associated with having short or long periods but were associated with irregular periods. A decrease in 25(OH)D of 10 ng/mL was associated with 1.9 times the odds of having irregular menstrual cycles (p = 0.04). Women whose 25(OH)D was below 20 ng/mL had almost two and a half times the odds of having irregular menstrual cycles compared with women who were above 20 ng/mL (p = 0.13).
The authors conclude,
“Lower levels of 25(OH)D were associated with irregular menstrual cycles in a population-based sample of late reproductive-aged women. Vitamin D may influence cycle regularity through its associations with AMH, insulin, androgens, or a yet to be identified pathway. Further investigation of potential mechanisms is warranted.”
As the authors point out, so many of the women had such low 25(OH)D levels that they could not find any 25(OH)D cutoff above which 25(OH)D was no longer associated with irregular periods.
These were women from the same city that houses the Food and Nutrition Board (FNB). The FNB advised that women this age only require 600 IU/day of vitamin D and that widespread vitamin D fortification is not necessary. It seems likely that 95% of these women had 25(OH)D levels lower than that recommended by the Endocrine Society (>40 ng/ml). Given vitamin D’s association with so many health conditions, now also irregular periods, it seems as if widespread fortification of vitamin D is needed in the home of the FNB.