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Women risk having their vitamin D levels fall when they stop using birth control pills or other contraceptives containing estrogen, new research indicates. This finding has clinical implications when counseling women who are planning to conceive and identifying women who may be at risk of deficiency.
Women risk having their vitamin D levels fall when they stop using birth control pills or other contraceptives containing estrogen, new research indicates.1 This finding has clinical implications when counseling women who are planning to conceive and identifying women who may be at risk of deficiency.1
Pregnant women are at high risk for vitamin D deficiency, due to the development of the fetus. During the first and second trimesters, the fetus develops most of its organ systems and is building the collagen matrix for its skeleton. During the last trimester, the fetus begins to calcify the skeleton, thereby increasing its calcium demand from the mother.2 Vitamin D deficiency increases the risk of preeclampsia and cesarean section.3,4
For the current research, designed as a cross-sectional data analysis, researchers analyzed data from the Study of Environment, Lifestyle, and Fibroids, a study of reproductive health in about 1,700 African-American women ages 23-34 in Detroit or the surrounding area. The participants answered questions about contraceptive use, as well as the amount of time they spent outdoors and use of vitamin D supplements. Study participants provided blood samples, which were analyzed to measure levels of 25-hydroxy vitamin D, the primary circulating form of vitamin D. Analysis results indicate that women who were using contraception containing estrogen tended to have higher vitamin D levels than other women, notes Quaker Harmon, MD, PhD, a postdoctoral fellow in the National Institutes of Health’s National Institute of Environmental Health Sciences in Research Triangle Park, NC.
“We could not find any behavioral differences such as increased time spent outdoors to explain the increase,” she said in a statement accompanying the research publication. “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.”
The mechanism for this increase is not well understood, say the researchers. In addition to elevations in 25-hydroxy vitamin D, exogenous estrogen has been associated with increases in the vitamin D binding protein, the active metabolite 1,25(OH)2 D, and the metabolically inactive 24,25(OH) vitamin D. Vitamin D binding protein is synthesized in the liver and may respond in a similar fashion to other estrogen-sensitive hepatic proteins, the researchers state.1
Daily doses of 600 international units (IU) do not prevent vitamin D deficiency in pregnant women. Recommendations issued by The Endocrine Society in Washington, DC, indicate pregnant women’s daily regimen should at least include a prenatal vitamin containing 400 IU of vitamin D with a supplement that contains at least 1,000 IU of vitamin D.2
Vitamin D supplementation during pregnancy has been suggested to safely improve pregnancy and infant outcomes. A 2016 Cochrane review of evidence looked at 15 randomized controlled trials involving 2,833 women. Nine trials compared the effects of vitamin D alone with no supplementation or a placebo, and six trials compared the effects of vitamin D and calcium with no supplementation.
The results suggest that the provision of vitamin D supplements during pregnancy improves the women’s vitamin D levels, as measured by 25-hydroxy vitamin D concentrations at term, and may reduce the risk of delivering a baby prematurely (less than 37 weeks of gestation), result in a lower risk of high blood pressure in women, and reduce the risk of a low birthweight baby (less than 2,500 g).5
In reproductive-age women planning a pregnancy, clinical testing of vitamin D levels should take into account recent contraceptive use, researchers in the current study note. After adjusting for seasonal exposure to sunlight, the researchers found the use of contraceptive pills, patches, or rings containing estrogen was associated with a 20% higher 25-hydroxy vitamin D level. While current birth control users tended to have higher levels of vitamin D in the blood, past contraceptive users had average levels of vitamin D.1
“Our findings indicate women may run the risk of developing vitamin D deficiency just when they want to become pregnant,” Harmon said. “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.”
Further research is needed to investigate endogenous estrogen effects, including how 25-hydroxy vitamin D levels might vary with changes such as the onset of puberty, pregnancy, and menopause.1
Consulting Editor Robert A. Hatcher, MD, MPH, Nurse Reviewer Melanie Deal, Editor Rebecca Bowers, and Executive Editor Joy Dickinson report no consultant, stockholder, speaker’s bureau, research, or other financial relationships with companies having ties to this field of study.