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.
PIP: This study was conducted to compare wintertime hyroxyvitamin D (250HD) levels among 66 young Caucasian women between ages 20 and 40 years from the Boston area who did and did not take oral contraceptives (OCs). Plasma 250HD was measured within a 2-month period and again after 1 year. Other measurements taken were height, weight, and intake of vitamin D from diet and supplements. The study demonstrated that the 250 HD levels of women who use OCs were as much as 24.1 nmol/l higher than those of non-OC users. This 41% difference decreased to 39% after adjustment for age and intake of vitamin D. All 5 women who discontinued OC use in the year after their initial measurement had reduced 250HD levels, while levels in the women whose OC use or non-use was constant remained unchanged throughout the study period. There were no significant associations between 250HD levels and ethinyl estradiol dosage, type of OC, or duration of use. In conclusion, OC use increases the circulating levels of 250HD of premenopausal adult women and should be taken into consideration when interpreting values obtained for clinical evaluation or nutrition research.