Table 4. Multivariable Associations Between Cumulative Total and Exclusive Breastfeeding and Early Menopause Among Parous Women in the Nurses’ Health Study II, 1989-2015a.
| Breastfeeding | Cases, No. | Person-Years | Model 1 | Model 2b | Model 3c | |||
|---|---|---|---|---|---|---|---|---|
| HR (95% CI) | P Value for Trend | HR (95% CI) | P Value for Trend | HR (95% CI) | P Value for Trend | |||
| Cumulative Total Breastfeeding Duration, mo | ||||||||
| <1 | 355 | 95 199 | 1 [Reference] | <.001 | 1 [Reference] | <.001 | 1 [Reference] | .01 |
| 1-6 | 313 | 92 804 | 0.99 (0.85-1.16) | 1.01 (0.87-1.18) | 1.0 (0.86-1.17) | |||
| 7-12 | 331 | 110 884 | 0.87 (0.75-1.01) | 0.90 (0.77-1.05) | 0.90 (0.78-1.05) | |||
| 13-18 | 231 | 82 977 | 0.81 (0.68-0.95) | 0.85 (0.72-1.0) | 0.87 (0.73-1.03) | |||
| 19-24 | 176 | 61 646 | 0.80 (0.66-0.95) | 0.86 (0.71-1.03) | 0.89 (0.74-1.07) | |||
| ≥25 | 335 | 125 846 | 0.73 (0.63-0.85) | 0.80 (0.68-0.93) | 0.84 (0.71-0.99) | |||
| Cumulative Exclusive Breastfeeding Duration, mo | ||||||||
| <1 | 737 | 202 123 | 1 [Reference] | <.001 | 1 [Reference] | <.001 | 1 [Reference] | .001 |
| 1-6 | 406 | 126 152 | 0.93 (0.82-1.05) | 0.95 (0.84-1.07) | 0.95 (0.84-1.07) | |||
| 7-12 | 280 | 116 419 | 0.67 (0.59-0.77) | 0.71 (0.61-0.81) | 0.72 (0.62-0.83) | |||
| 13-18 | 140 | 54 207 | 0.72 (0.60-0.86) | 0.77 (0.64-0.92) | 0.80 (0.66-0.97) | |||
| ≥19 | 70 | 24 282 | 0.77 (0.60-0.98) | 0.84 (0.65-1.07) | 0.89 (0.69-1.16) | |||
Abbreviation: HR, hazard ratio.
Exclusive breastfeeding was defined as when the infant received breast milk only, with no other liquids or solids given. Total breastfeeding includes all breastfeeding, both exclusive and nonexclusive. Data were from 63 357 parous women who provided information on breastfeeding, of whom 59 388 provided information on exclusive breastfeeding.
Adjusted for age, age at menarche (ie, ≤9, 10, 11, 12, 13, 14, 15, 16, or ≥17 years), smoking status (ie, never, past [1-14, 15-24, or ≥25 years], or current [1-14, 15-24, or ≥25 years]), alcohol intake (ie, 0, 1 to <10, 10 to <30, or ≥30 g/d), vegetable protein intake (in quintiles), body mass index (ie, <18.5, 18.5-24.9, 25.0-29.9, or ≥30), vitamin D from dairy foods (in quintiles), supplemental vitamin D (ie, 0, >0 to <600, or ≥600 IU/d), OC use (ie, never, past, or current), duration of OC (ie, never, 1-23, 24-47, 48-71, 72-95, 96-119, ≥120 months, or missing), and infertility because of ovulatory disorder (ie, yes or no).
Additionally adjusted for parity (ie, 0, 1, 2, 3, or ≥4).