A recent study published in the Journal of Clinical Endocrinology & Metabolism found that the use of an estrogen containing birth control is associated with a 20% increase in vitamin D status.

Approximately 28% of women of reproductive age, or 10.6 million women, use oral contraceptives in the United States. Multiple studies have suggested that the use of oral contraceptives containing estrogen is related to higher vitamin D levels. However, these studies have been limited due to their small sample size (less than 150 individuals) and inability to account for confounding factors, such as supplement use and sun exposure. A recent study examined this relationship further, consisting of 1662 African American women and controlling for a multitude of confounders.

The researchers assessed the vitamin D status of 1662 African American women between the ages of 23-34 years old. At the clinic visit, women brought all medications, vitamins, minerals and herbal supplements they had used in the past 24 hours. The participants were asked about the use of contraception, multivitamins, vitamin D supplements or cod liver oil through a four-week questionnaire. Women also filled out a Food Frequency Questionnaire to gather more information on vitamin D intake via diet and supplementation. In addition, telephone and computer based questionnaires gathered data on a wide range of confounding factors, such as the amount of time spent outdoors, vacation time in sunny locations and sunscreen use. This extensive data collection permitted the researchers to adjust for a total of 43 variables, allowing them to better isolate the relationship between vitamin D status and the use of oral contraceptives.

Here is what the researchers found:

• A total of 40% of the women used a supplement containing vitamin D. Yet, the average vitamin D status was 15.7 ng/ml, which is considered severely vitamin D deficient by most.
• After adjusting for 43 variables, the use of estrogen containing contraceptive was associated with a 20% higher vitamin D status.
• The relationship between vitamin D status and the pill was greater in magnitude than the low dose vitamin D supplement ( 200 IU/day), which was associated with a 14% higher vitamin D status.
• There was no relationship between vitamin D status and past use of estrogen containing oral contraceptives. This indicated that the relationship between current use of the pill and vitamin D status was unlikely to occur due to confounding factors related to contraceptive choice.

The researchers concluded,

“Using detailed information from 1662 young African American women in the Detroit area, we provide strong evidence to support the hypothesis that exogenous estrogen use increases serum 25(OH)D.”

The lead researcher, Quaker E. Harmon, MD, PhD, stated,

“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.”

Citation

Tovey, A & Cannell, JJ. Estrogen increase vitamin D levels. The Vitamin D Council Blog & Newsletter, August 10, 2016.

Source

Harmon, Q. et al. Use of Estrogen-Containing Contraception Is Associated With Increased Concentrations of 25-Hydroxy Vitamin D. Journal of Clinical Endocrinology & Metabolism, 2016.