TABLE 5.
Total dietary vitamins C and E, ferric-reducing ability of plasma (FRAP), and the risk of glioma in the Health Professionals Follow-Up Study (HPFS; 1986–2004), the Nurses’ Health Study I (NHS I; 1980–2004), and NHS II (1991–2005)
| Quintile of intake |
||||||
| 1 | 2 | 3 | 4 | 5 | P for trend1 | |
| Vitamin C (mg/d)2 | ||||||
| Cases | 64 | 54 | 77 | 76 | 64 | |
| Person-years | 809,330 | 828,618 | 824,802 | 828,020 | 810,776 | |
| RR (95% CI)3 | 1.0 | 0.77 (0.54, 1.12) | 1.09 (0.78, 1.53) | 1.05 (0.75, 1.47) | 0.88 (0.62, 1.26) | 0.67 |
| Vitamin E (mg/d)2 | ||||||
| Cases | 62 | 60 | 79 | 63 | 71 | |
| Person-years | 809,448 | 818,459 | 820,562 | 843,170 | 809,910 | |
| RR (95% CI)3 | 1.0 | 0.93 (0.65, 1.34) | 1.19 (0.84, 1.67) | 0.91 (0.58, 1.42) | 0.98 (0.67, 1.43) | 0.72 |
| FRAP (mmol/d)2 | ||||||
| Cases | 66 | 80 | 56 | 66 | 67 | |
| Person-years | 805,989 | 824,369 | 831,714 | 830,220 | 809,256 | |
| RR (95% CI)3 | 1.0 | 1.08 (0.71, 1.64) | 0.76 (0.53, 1.09) | 0.90 (0.63, 1.27) | 0.90 (0.64, 1.28) | 0.35 |
Based on the median value of each intake category and modeling these as continuous variables in a Cox proportional hazards model.
Cutoffs for quintiles were different for each cohort and are based on cumulative updated averages over the follow-up periods: vitamin C (HPFS: 155, 226, 364, and 696; NHS I: 138, 192, 279, and 500; NHS II: 119, 164, 233, and 428), vitamin E (HPFS: 11, 19, 64, and 164; NHS I: 9, 18, 53, and 160; NHS II: 9, 14, 26, and 117), and FRAP (HPFS: 9, 12, 14.5, and 19; NHS I: 9, 11, 13.5, and 17; NHS II: 7, 10, 12, and 15).
Rate ratios (RRs) and 95% CIs from Cox proportional hazards models were adjusted for age and caloric intake (quintiles). Results were obtained from pooling the β coefficient and SE estimates by using the DerSimonian and Laird random-effects model; no significant evidence of heterogeneity by cohort was observed (α = 0.05).