Researchers determine that taking estrogen-containing birth control pills increases Vitamin D levels and discontinuing them causes Vitamin D levels to plummet.

The main function of vitamin D is to provide the body with an ample supply of calcium, and maintain accurate levels of phosphorous levels in the blood. Calcium also supports strong bones, and teeth, which is important for pregnant or nursing women. Although Vitamin D can be increased by eating fish, eggs, and other foods rich in Vitamin D, about 90% of Vitamin D is produced through the skin, after being exposed to sunlight. The absence of sufficient Vitamin D can lead to rickets, a softening of the bones, which is why pregnant women need to maintain the correct level of Vitamin D during pregnancy.

National Institute of Environmental Health Sciences in Research personnel, Dr. Quaker E. Harmon, began investigating changes in vitamin D levels in women taking oral contraceptives. This investigation coincides with data gathered from studies of nearly 1,700 African-American women aged 23 through 34, living in or around the Detroit, Michigan area. The study gathered information about these women’s contraceptive usage, sunlight exposure, and Vitamin D intake. More than 1,662 women participated in giving blood samples to help measure their level of Vitamin D, using a test called 25-hydroxy vitamin D.

Vitamin D Important for Normal Fetal and Skeleton Development

Even after controlling factors that can lead to Vitamin D deficiency, pregnant women still have an increased risk of developing Vitamin D deficiency, and a higher risk of developing bone disease. Scientists are baffled, because according to research there is no reason for such deficiency. However, their finding did conclude that contraceptives containing estrogen did boost Vitamin D levels, and decreased when women stopped taking their contraceptives. After making some adjustments with the use of patches, rings and birth control pills containing estrogen, these women showed a 20% increase in Vitamin D levels, as opposed to past users who had average levels of Vitamin D.

Advice for Women Planning to Become Pregnant

The study, posted in the Journal of Clinical Endocrinology and Metabolism, states that women who are trying to get pregnant have a greater risk of becoming Vitamin D deficient. Dr. Harmon adds that if these women are making plans to stop taking their birth control pills, they should go the extra step to ensure that they are consuming enough Vitamin D to meet their body’s need.

When News Today, asked Dr. Harmon about the estrogen discrepancy and how it affects Vitamin D levels, she stated that there is no known reason why Vitamin D levels are higher. However, she did state that this increase could be due to changes in the metabolism of Vitamin D in women who use contraceptives containing estrogen.

As for the studies that solely tested African-American women, the tests were conclusive. However, similar testing conducted on other races revealed the same results, so the race association is ruled out. Nevertheless, studies do suggest that African-American women are more likely to experience Vitamin D deficiency, and even the smallest change in increase or decrease is important for overall bone structure.

Dr. Harmon states, she will continue to follow this particular group of women, and will be investigating Vitamin D efficiency in relationship to menstrual cycles.

Quaker E. Harmon, David M. Umbach, Donna D. Baird. Use of Estrogen-Containing Contraception Is Associated With Increased Concentrations of 25-Hydroxy Vitamin D. The Journal of Clinical Endocrinology & Metabolism, 2016; jc.2016-1658 DOI: 10.1210/jc.2016-1658