Objectives Ovarian cancer is the second most common female genital cancer in Nigeria. This study aimed to determine the association between serum vitamin D level and risk of ovarian cancer in women in Lagos, Nigeria.

Methods We conducted a cross-sectional study from the 1st August 2016 to 31st May 2017. Demographic characteristics including type of clothing, average hours spent outdoors and skin complexion of 35 women with primary epithelial ovarian cancer and 35 apparently healthy women were obtained using questionnaires. Venous blood was taken from each participant to determine serum 25-hydroxyvitamin D [25(OH)D] level using vitamin D ELISA kit. Mann-Whitney U and Chi square tests were used to compare the median 25(OH)D levels among the two groups. Binary logistic regression analysis were conducted to evaluate the relationship between vitamin D levels and the risk of ovarian cancer.

Results The mean age of the participants was 50.6(±11.1) years. The incidence of vitamin D deficiency (≤20ng/ml) among all the participants was high (62.9%) but the median vitamin D level in the ovarian cancer patients was lower as compared to the healthy women (13.5ng/ml, 95%CI: 9.2 –21.2 vs 20.0ng/ml, 95% CI: 13 - 37.2, p-value =0.0061 respectively). Vitamin D deficiency was associated with a four-fold risk of developing epithelial ovarian cancer (p-value =0.049).

Conclusions This study revealed that low circulating 25(OH)D levels may be associated with the risk of epithelial ovarian cancer. We recommended a large prospective longitudinal study to evaluate the association between serum vitamin D levels and epithelial ovarian cancers in women in Nigeria.