My mom and I were both tested for our vitamin D levels and we both came back extremely low. You are supposed to have a blood level between 20-50 and hers was 9 and mine was 4. She had PCOS and had suffered for a long time with irregular periods. My cycles were very irregular also and doctors thought that I might have PCOS as well. I am 16 and had stopped menstruating for over 6 months. We were both put on major vitamin D supplementation and gluten free diets and the doctor thought that our vitamins were possibly being lost because of celiac disease. Her periods became normal and regular, and after not having any periods since early December, I got mine a few days ago. It's just surprising that vitamin D would have such a strong connection to the menstrual cycle. Have any of you ever heard of this before?