Aside from the obvious effect, the birth-control pill can do all sorts of amazing things, including help prevent some forms of cancer. Now, a new study suggests that taking hormonal contraception may also increase vitamin D levels. For the study, published today in the Journal of Clinical Endocrinology & Metabolism, researchers looked at data from 1,662 African-American women (ages 23-34) who took part in a previous study. Between 2010 and 2012, all the participants provided a blood sample and completed basic health and demographic questionnaires. As part of that, the researchers collected data on whether or not participants used any form of hormonal birth control or any type of nutritional supplements. The results showed that women who were currently taking hormonal contraception that contained oestrogen had slightly higher levels of vitamin D in their blood samples. Although the researchers aren't sure exactly what's causing the effect, the fact that only current use of birth control (not past use) was associated with the increase suggests that the oestrogen in the pills is playing a major role. Normally, our skin produces vitamin D in response to sunlight. Then it’s converted into a form that our bodies can use to improve calcium absorption so we can maintain strong bones. But other studies have shown that oestrogen might be changing the way our bodies create and process the vitamin. "It’s a very complicated metabolic pathway, and [oestrogen] may be acting at any point on that pathway,” explains Quaker Harmon, MD, Phd, lead author on the study. "If [oestrogen] enhances production in the skin, you would have more of the early forms of vitamin D, and if it increases how long the vitamin D stays around in the serum or decreases how quickly it's cleared from your serum, that would also increase your levels." However, compared to taking vitamin D supplements, the effect of hormonal contraception was small. Dr. Harmon explains that it was a 20% increase, approximately equal to that of regularly taking a 200 IU supplement. However, those who regularly took supplements of higher doses saw a 50-70% increase over those who didn't. So the researchers here aren't recommending anyone take hormonal contraception purely for the vitamin D bump. But this finding could be especially important for women who have been taking birth control and are interested in becoming pregnant. If they have naturally low vitamin D levels, this study suggests that going off contraception may cause a surprising and potentially dangerous drop. Aside from the usual benefits of vitamin D for the mother, it's also necessary for proper growth of the foetal skeleton. So if you're planning to transition from contraception to conception anytime soon, check in with your doctor about your vitamin D.