Table 1. Characteristics of the included studies about vitamin C intake on ovarian cancer risk.
| Study, year | Design | Age | Participants, Cases | Country | Category | RR (95%CI) | Adjustment |
|---|---|---|---|---|---|---|---|
| Slattery et al., 1989 | PBCC | 20–79 | 577,85 | United States | >159.1 vs. <97.8 mg/d | 0.7 (0.3–1.4) | Adjusted for age, body mass index of weight/height2, and number of pregnancies. All dietary variables are in separate logistic models. |
| Tzonou et al., 1993 | HBCC | 18–75 | 389,189 | Greece | Highest vs. lowest | 0.90 (0.76–1.06) | Adjusted for age, years of schooling, parity, age at first birth, menopausal status as well as for energy intake |
| Kushi et al., 1999 | Cohort | 55–69 | 29,083,139 | United States | >321.9 vs. <129.2 mg/d | 1.05 (0.63–1.76) | Adjusted for age, total energy intake, number of live births, age at menopause, family history of ovarian cancer in a first-degree relative, hysterectomy/unilateral oophorectomy status, waist-to-hip ratio, level of physical activity, cigarette smoking (number of pack-years), and educational level |
| Cramer et al., 2001 | PBCC | >50 | 1,065,549 | United States | >337 vs. ≤97 mg/d | 1.00 (0.66–1.53) | Adjusted for total caloric intake, age, site, parity, body mass index, oral contraceptive use, family history of breast, ovarian or prostate cancer in a first-degree relative, tubal ligation, education, and marital status |
| Fairfield et al., 2001 | Cohort | 30–55 | 80,326,301 | United States | Q5 vs. Q1 | 1.22 (0.83–1.81) | Adjusted for age, body mass index (kg/m2), duration of oral contraception use, smoking history, parity, history of tubal ligation, and caffeine intake |
| Fleischauer et al., 2001 | HBCC | ≥18 | 419,168 | United States | >180 vs. <100 mg/d | 1.04 (0.57–1.92) | Adjusted for age, parity, body mass index, total caloric intake, and family history of breast and/or ovarian cancer |
| McCann et al., 2001 | HBCC | 20–87 | 1,921,496 | United States | >250 vs. ≤112 mg/d | 0.69 (0.47–1.03) | Adjusted for age, education, region of residence, regularity of menstruation, family history of ovarian cancer, parity, age at menarche, oral contraceptive use, and total energy intake |
| Salazar-Martinez et al., 2002 | HBCC | 20–79 | 713,84 | Mexico | ≥184 vs. ≤78 mg/d | 1.28 (0.72–2.28) | Adjusted for age, total energy intake, number of live births, recent changes in weight, physical activity, and diabetes |
| McCann et al., 2003 | PBCC | 40–85 | 820,124 | United States | >244 vs. <123 mg/d | 0.82 (0.42–1.59) | Adjusted for age, education, total months menstruating, difficulty becoming pregnant, oral contraceptive use (ever/never), menopausal status, and total energy |
| Zhang et al., 2004 | HBCC | 18–75 | 906,254 | China | ≥140.25 vs. ≤66.50 mg/d | 0.31 (0.18–0.53) | Adjusted for terms for age, locality, education, family income, BMI, total energy intake, tobacco smoking, alcohol consumption, ovarian cancer in first degree relatives, parity, menopausal status, and oral contraceptive use |
| Tung et al., 2005 | PBCC | 45–75 | 1,165,558 | United States | Q4 vs. Q1 | 0.89 (0.62–1.26) | Adjusted for age, ethnicity, study site, education, oral contraceptive pill use, pregnancy status, tubal ligation, and energy intake by polytomous logistic regression (histologic type), or unconditional logistic regression (all other variables) |
| Silvera et al., 2006 | Cohort | 40–59 | 89,835,264 | Canada | >206 vs. <115 mg/d | 0.90 (0.58–1.37) | Adjusted for age, menopausal status, use of oral contraceptives, body mass index, education, participation in vigorous physical activity, energy intake at baseline, study center, and randomization group |
| Chang et al., 2007 | Cohort | <84 | 97,275,280 | United States | >665 vs. ≤75 mg/d | 1.96 (1.11–3.46) | Adjusted for race, total energy intake, parity, oral contraceptive use, strenuous exercise, wine consumption, and menopausal status/hormone therapy use; stratified by age at baseline |
| Thomson et al., 2008 | Cohort | 50–79 | 133,614,451 | United States | >130 vs. <58 mg/d | 1.07 (0.77–1.48) | Adjusted for age, log calories, No. breast/ovary cancer relatives, dietary modification randomization arm, hysterectomy status, minority race, pack-years smoking, physical activity, nonsteroidal anti-inflammatory drug use, parity, infertility, duration of oral contraceptive use, lifetime ovulatory cycles, partial oophorectomy, age at menopause, and HT usage at entry |
| Gifkins et al., 2012 | PBCC | >21 | 595,205 | United States | >141.8 vs. <82.3 mg/d | 1.29 (0.72–2.29) | Adjusted for age (continuous), education, race, age at menarche (continuous), menopausal status and age at menopause for postmenopausal women, parity, OC use, HRT use, BMI (continuous), tubal ligation, and total calories, physical activity (METs), and smoking status |
| Terry et al., 2017 | PBCC | 20–79 | 1,038,406 | United States | >142.1 vs. <57.0 mg/d | 1.05 (0.66–1.69) | Adjusted for age, region, education, parity, oral contraceptive use, menopause, tubal ligation, family history, BMI, smoking status, total energy, and physical activity |
Abbreviations: CI, confidence intervals; HBCC, hospital-based case–control study; PBCC, population-based case–control study; RR, relative risk.