Table 4. Pooled multivariable relative risks (95% CI)* for quintiles of daily servings of foods high in nitrate in relation to all primary open-angle glaucoma (POAG) and POAG with early paracentral visual field loss (“Para-POAG”) in Nurses' Health Study (1984-2012) and in Health Professionals' Follow-up Study (1986-2012).
| Quintiles of intake of foods [median servings per day] | ||||||||
|---|---|---|---|---|---|---|---|---|
| % Variability in nitrate explained | Outcome | Q1 | Q2 | Q3 | Q4 | Q5 | p-trend | |
| Green leafy vegetables† | 56.7% | Median | 0.31 | 0.56 | 0.75 | 1.00 | 1.45 | |
| All POAG | 1.00 (ref) | 0.95 (0.81, 1.12) | 0.90 (0.66, 1.22) | 0.93 (0.61, 1.44) | 0.82 (0.69, 0.97) | 0.02 | ||
| Para-POAG | 1.00 (ref) | 0.89 (0.57, 1.41) | 0.67 (0.49, 0.92) | 0.69 (0.51, 0.93) | 0.52 (0.29, 0.96) | 0.0002 | ||
| Iceberg lettuce | 23.2% | Median | 0.11 | 0.25 | 0.43 | 0.55 | 0.86 | |
| All POAG | 1.00 (ref) | 1.00 (0.83, 1.20) | 1.03 (0.87, 1.23) | 0.88 (0.69, 1.13) | 0.89 (0.75, 1.06) | 0.06 | ||
| Para-POAG | 1.00 (ref) | 1.03 (0.63, 1.70) | 0.89 (0.56, 1.42) | 0.72 (0.41, 1.26) | 0.69 (0.49, 0.97) | 0.001 | ||
| Romaine lettuce | 17.4% | Median | 0.00 | 0.05 | 0.12 | 0.25 | 0.55 | |
| All POAG | 1.00 (ref) | 0.93 (0.77, 1.11) | 0.98 (0.82, 1.15) | 0.89 (0.76, 1.05) | 0.87 (0.74, 1.03) | 0.11 | ||
| Para-POAG | 1.00 (ref) | 1.10 (0.61, 1.97) | 1.17 (0.48, 2.89) | 1.01 (0.66, 1.55) | 0.71 (0.29, 1.75) | 0.19 | ||
| Kale/mustard/chard greens‡ | 6.0% | Median | 0.00 | 0.01 | 0.04 | 0.07 | 0.13 | |
| All POAG | 1.00 (ref) | 1.02 (0.84, 1.24) | 0.96 (0.77, 1.19) | 0.92 (0.61, 1.38) | 0.72 (0.54, 0.95) | 0.08 | ||
| Para-POAG | 1.00 (ref) | 0.97 (0.68, 1.39) | 1.03 (0.70, 1.53) | 1.09 (0.66, 1.80) | 0.33 (0.16, 0.69) | 0.01 | ||
| Cruciferous vegetables† | 15.9% | Median | 0.16 | 0.29 | 0.42 | 0.58 | 0.90 | |
| All POAG | 1.00 (ref) | 1.28 (1.08, 1.52) | 1.10 (0.87, 1.38) | 1.10 (0.92, 1.32) | 1.12 (0.94, 1.35) | 0.93 | ||
| Para-POAG | 1.00 (ref) | 1.23 (0.90, 1.69) | 1.04 (0.75, 1.45) | 1.15 (0.83, 1.59) | 1.02 (0.73, 1.43) | 0.72 | ||
| Root vegetables†§ | 9.7% | Median | 0.50 | 0.77 | 1.00 | 1.29 | 1.76 | |
| All POAG | 1.00 (ref) | 0.88 (0.73, 1.05) | 0.83 (0.63, 1.09) | 0.94 (0.64, 1.40) | 0.87 (0.56, 1.36) | 0.77 | ||
| All POAG-women | 1.00 (ref) | 0.88 (0.71, 1.09) | 0.93 (0.75, 1.15) | 1.13 (0.91, 1.40) | 1.07 (0.85, 1.35) | 0.12 | ||
| All POAG-men | 1.00 (ref) | 0.88 (0.64, 1.21) | 0.70 (0.50, 0.97) | 0.76 (0.54, 1.05) | 0.68 (0.48, 0.96) | 0.04 | ||
| Para-POAG | 1.00 (ref) | 0.74 (0.48, 1.15) | 0.83 (0.59, 1.15) | 0.85 (0.27, 2.65) | 0.84 (0.34, 2.08) | 0.89 | ||
| Para-POAG-women | 1.00 (ref) | 0.88 (0.58, 1.35) | 0.84 (0.55, 1.28) | 1.48 (0.99, 2.20) | 1.29 (0.84, 1.98) | 0.03 | ||
| Para- POAG-men | 1.00 (ref) | 0.56 (0.31, 1.02) | 0.80 (0.46, 1.37) | 0.46 (0.25, 0.86) | 0.51 (0.27, 0.96) | 0.04 | ||
| Celery | 6.5% | Median | 0.02 | 0.07 | 0.11 | 0.23 | 0.44 | |
| All POAG | 1.00 (ref) | 0.88 (0.73, 1.06) | 0.88 (0.63, 1.22) | 0.92 (0.77, 1.10) | 0.93 (0.78, 1.11) | 0.74 | ||
| Para-POAG | 1.00 (ref) | 0.80 (0.56, 1.14) | 0.76 (0.55, 1.05) | 0.72 (0.47, 1.13) | 0.93 (0.68, 1.27) | 0.79 | ||
| Tomato – based foods† | 4.0% | 0.21 | 0.37 | 0.53 | 0.71 | 1.02 | ||
| All POAG | 1.00 (ref) | 0.97 (0.83, 1.14) | 0.89 (0.75, 1.05) | 0.86 (0.73, 1.02) | 0.90 (0.75, 1.07) | 0.14 | ||
| Para-POAG | 1.00 (ref) | 0.94 (0.69, 1.28) | 0.89 (0.65, 1.22) | 1.02 (0.57, 1.80) | 0.84 (0.60, 1.17) | 0.37 | ||
Abbreviations: RR = Relative Risk; CI = Confidence Interval
Intake calculated using cumulative average (i.e., average of all available intake data from food frequency questionnaires completed before each two-year period at risk). Pooled results were calculated using Dersimonian and Laird methods with random effects; p for heterogeneity between cohorts for all p for linear trend results were > 0.05. All multivariable analyses were adjusted for the same variables as in Model 1 in Table 2.
Kale/mustard/chard greens were included in both the green leafy vegetable and cruciferous vegetable categories. Green leafy vegetables included iceberg lettuce, romaine lettuce, kale/mustard/chard greens, cooked spinach, raw spinach. Cruciferous vegetables included broccoli, cabbage/coleslaw, cauliflower, kale/mustard/chard greens, Brussels sprouts. Root vegetables included potato, beet, onion, carrot and yam / sweet potatoes. Tomato-based foods included whole tomato, tomato sauce and tomato juice.
The results for women and men were heterogeneous (p for heterogeneity was 0.01 for all POAG, and it was 0.004 for all Para-POAG); thus, cohort specific results are also provided. For all other food groups, the p for heterogeneity were >0.5