Abstract
Given the poor prognosis of ovarian cancer and limited population-level strategies for early detection and long-term treatment success, knowledge of modifiable risk factors for prevention and improved prognosis is important. Vitamin D has received wide scientific interest in cancer research as having the potential to be one such factor. We carried out a systematic narrative review of the literature on vitamin D and ovarian cancer risk and survival. We included 17 case-control and cohort studies on ovarian cancer incidence. Five analyses were of sun exposure, among which three reported an inverse association. Of 11 analyses of dietary vitamin D, two reported an inverse association. Among five studies of 25(OH)D levels, an inverse association was reported in two. Across all studies the findings were inconsistent, but some recent studies have suggested that vitamin D exposure at earlier ages may be important. Only three studies examining vitamin D exposure in relation to survival among ovarian cancer survivors were identified and the findings were inconsistent. The evidence to date supports a null influence of vitamin D on both ovarian cancer risk and survival. Future research should ensure that exposure assessment captures vitamin D exposure from all sources and for the etiologically or prognostically pertinent period.
Highlights
Worldwide, ovarian cancer is the eighth most frequently diagnosed cancer among women, but incidence rates vary geographically, with the highest rates in Europe and North America, and the lowest in Africa and Asia [1]
Score based on the Newcastle-Ottawa Scale; 2 The category of reference is an intermediate level of exposure; 3 This study reported on two cohort studies, the Nurses’ Health Study (NHS)
1 Score based on the Newcastle-Ottawa Scale; 2 Cramer, 2001 and Merritt, 2013 represent the same study population; 3 This study reported on two cohort studies, the Nurses’ Health Study (NHS) and the Nurses’ Health Study II (NHSII); 4 Cohort size at mid-point of follow-up; 5 In this pooled analysis of 12 cohort studies, 7 had assessed total vitamin D intake; table entries on cohort size and number of cases refer strictly to the analysis of total vitamin D
Summary
Ovarian cancer is the eighth most frequently diagnosed cancer among women, but incidence rates vary geographically, with the highest rates in Europe and North America, and the lowest in Africa and Asia [1]. The poor prognosis is a consequence of the fact that most ovarian cancers are aggressive such that, at diagnosis, the disease has spread beyond the pelvis reducing the chances of long-term treatment success. Prevention is of critical importance in controlling ovarian cancer, but few modifiable risk factors are known. The only factors known to influence survival are clinical or biological in nature, such as age at diagnosis and stage, grade and histology of the cancer, and are not modifiable. Vitamin D has received wide scientific interest in cancer prevention research [2,3]. Diet constitutes a source of both vitamin D2 (ergocalciferol) and vitamin D3 [4,5] through natural sources (e.g., fish, eggs), fortified foods (e.g., milk, breakfast cereals) and supplements [6]. Vitamins D2 and D3 are converted in the liver to 25-hydroxyvitamin D (25(OH)D: calcidiol), the circulating form of
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