When women drop birth control pills, their vitamin D levels may also drop, according to research from the National Institutes of Health. And while there’s no good time in life to be vitamin D deficient, lacking adequate levels of the vitamin is particularly dangerous during pregnancy, when women need more D to support the formation of the fetal skeleton.
"Our study found that women who were using contraception containing estrogen tended to have higher vitamin D levels than other women," the study’s author, Quaker E. Harmon, MD, PhD, of the NIH's National Institute of Environmental Health Sciences, said in a release from the Endocrine Society. “We could not find any behavioral differences such as increased time spent outdoors to explain the increase. Our findings suggest that contraceptives containing estrogen tend to boost vitamin D levels, and those levels are likely to fall when women cease using contraception.”
For the study, researchers analyzed data from the Study of Environment, Lifestyle & Fibroids, a study of reproductive health in nearly 1,700 African American women between the ages of 23 and 34. Researchers measured the vitamin D in their blood, and the women filled out questionnaires about contraceptive use, time outside and vitamin D supplements they might have taken. After adjusting for seasonal exposure to sunlight, the researchers found the use of contraceptive pills, patch or ring containing estrogen was associated with a 20 percent higher 25-hydroxy vitamin D level. That level dropped dramatically after they stopped using contraception.
"Our findings indicate women may run the risk of developing vitamin D deficiency just when they want to become pregnant," said Harmon. "For women who are planning to stop using birth control, it is worth taking steps to ensure that vitamin D levels are adequate while trying to conceive and during pregnancy." The study results were published in the Journal of Clinical Endocrinology & Metabolism.