TABLE 2.
Multivariable-adjusted joint associations between total daily intakes of folate and other dietary factors and postmenopausal breast cancer risk among women in the VITAL (VITamins And Lifestyle) Study between 2000 and 20061
| Tertile of 10-y total folate intake |
||||||||
| 1 (45 to <560 DFE/d) |
2 (560 to <989 DFE/d) |
3 (989–3620 DFE/d) |
||||||
| Cases | Multi-RR (95% CI) | Cases | Multi-RR (95% CI) | Cases | Multi-RR (95% CI) | P for trend2 | P for interaction3 | |
| Dietary methionine | ||||||||
| Median, low | 144 | 1.00 | 115 | 0.93 (0.73, 1.19) | 90 | 0.88 (0.67, 1.15) | 0.38 | |
| High | 78 | 0.83 (0.62, 1.12) | 116 | 0.87 (0.65, 1.16) | 116 | 0.67 (0.50, 0.90) | 0.09 | 0.58 |
| Total riboflavin | ||||||||
| Median, low | 203 | 1.00 | 109 | 0.95 (0.75, 1.20) | 17 | 0.91 (0.55, 1.49) | 0.65 | |
| High | 19 | 1.01 (0.62, 1.62) | 122 | 1.02 (0.80, 1.28) | 189 | 0.82 (0.67, 1.02) | 0.10 | 0.42 |
| Total vitamin B-6 | ||||||||
| Median, low | 207 | 1.00 | 116 | 0.90 (0.72, 1.14) | 6 | 0.69 (0.31, 1.56) | 0.19 | |
| High | 15 | 0.80 (0.47, 1.35) | 115 | 1.04 (0.82, 1.31) | 200 | 0.82 (0.67, 1.01) | 0.25 | 0.98 |
| Total vitamin B-12 | ||||||||
| Median, low | 194 | 1.00 | 102 | 0.91 (0.71, 1.16) | 27 | 0.86 (0.57, 1.29) | 0.25 | |
| High | 28 | 1.01 (0.68, 1.51) | 129 | 1.05 (0.84, 1.32) | 179 | 0.83 (0.66, 1.03) | 0.13 | 0.54 |
| Modified micronutrient score, without folate4 | ||||||||
| Median, low | 183 | 1.00 | 115 | 1.00 (0.79, 1.26) | 33 | 0.93 (0.64, 1.35) | 0.57 | |
| High | 39 | 1.15 (0.80, 1.64) | 116 | 1.02 (0.79, 1.31) | 173 | 0.84 (0.67, 1.06) | 0.05 | 0.22 |
| Alcohol | ||||||||
| <10 g/d | 170 | 1.00 | 164 | 0.92 (0.74, 1.14) | 165 | 0.86 (0.69, 1.08) | 0.19 | |
| ≥10 g/d | 52 | 1.47 (1.07, 2.01) | 67 | 1.73 (1.29, 2.32) | 41 | 1.05 (0.73, 1.50) | 0.16 | 0.78 |
Multivariable-adjusted relative risks (multi-RRs) and associated 95% CIs were estimated by using a Cox regression model adjusted for age (y), race (white or other), family history of breast cancer (none, 1 affected mother or sister, or ≥2 affected mother or sisters), mammography within 2 y preceding baseline(no or yes), history of breast biopsy (no or yes), age at menarche (≤11, 12, 13, or ≥14 y), age at first birth (nulliparous, or ≤19, 20–24, 25–34, or ≥35 y), age at menopause (≤44, 45–49, or ≥50 y), years of combined estrogen and progestin postmenopausal hormone use (never or <1, 1–4, 5–9, or ≥10), BMI (in kg/m2; <25, 25 to <30, or ≥30), height (<62, 62 to <65, 65 to <68, or ≥68 in.; 1 in. = 2.54 cm), total physical activity (none, 1–3 tertiles of metabolic equivalent hours/wk), and alcohol intake in the past year (<1.5, 1.5–4.9, 5.0–9.9, or ≥10 g/d). We additionally adjusted for total energy intake (kcal/d) in analyses of dietary and total nutrient intakes. Total intake was calculated as the sum of dietary intakes over the year before baseline plus the 10-y average from supplements.
Calculated by modeling categories of total folate as a single ordinal variable in a Cox regression; a Wald test was used to obtain a P value.
P for interaction tested whether the association between total folate intake and breast cancer risk was modified by nutrient or alcohol intake. The Wald test was used to assess the significance of the interaction term.
Modified micronutrient score computed by summing the z scores of methionine, riboflavin, and vitamins B-6 and B-12 and then dividing this sum into tertiles.