The Association of Oral Contraceptive Use with Plasma 25-hydroxyvitamin D Levels

OBJECTIVE: This analysis was conducted to compare wintertime 25-hydroxyvitamin D (25OHD) levels of young women who did and did not use oral contraceptives (OC). METHODS: The subjects were 66 Caucasian women aged 20 through 40 recruited from the Boston area. Plasma 25OHD was measured in February or March and again 1 year later. Other measurements included height, weight and vitamin D intake from diet and supplements. RESULTS: The initial mean 25OHD level of the 26 OC users was 41% higher than those of nonusers before adjustment for age and vitamin D intake (83 +/- 40 (sd) nmol/L compared with 59 +/- 22), and 39% higher after adjustment (p = 0.003). Five women who discontinued OC use during the year following their initial measurement all had decreases in their 25OHD levels (mean change was -25.5 +/- 17.7 (SD) nmol/L), whereas levels in women whose OC use or non-use was constant did not change. CONCLUSION: OC use increases circulating levels of 25OHD, and should be considered when interpreting values obtained for clinical evaluation or nutrition research.