Table 3.
Risk of Early Menopause in NHS2 According to Menstrual Cycle Length and Regularity at Ages 18–22 Years: Results of Cox Proportional Hazards Models
| Regularity | Length (days) | Case Subjects, No. | PY | Adjusted HRa | 95% CI |
|---|---|---|---|---|---|
| Regular/very regular | 26–31 | 849 | 447,198 | 1.00 | REF |
| <26 | 182 | 55,076 | 1.64 | 1.40 to 1.93 | |
| >31 | 72 | 68,157 | 0.61 | 0.48 to 0.78 | |
| Usually irregular | <32 | 89 | 43,916 | 1.19 | 0.94 to 1.49 |
| ≥32 | 52 | 71,821 | 0.50 | 0.37 to 0.66 | |
| Always irregular/no periods | <32 | 30 | 11,468 | 1.61 | 1.10 to 2.34 |
| ≥32 | 49 | 66,837 | 0.50 | 0.37 to 0.68 |
Abbreviations: PY, person-y; REF, referent.
a
Adjusted model included age; smoking (categories: never, past, and current status; ≤14, 15–24 or ≥25 cigarettes per d); alcohol consumption (0, 0.1–10, >10–30, >30 g/d); parity (0, 1–2, ≥3); duration of breastfeeding (0, 1–3, >3–6, >6–12, >12–18, >18–24, >24–36, >36 mos); percentage of calories from vegetable protein (quintiles); BMI (American Dietary Association categories); dairy and supplemental sources of vitamin D (quintiles); age at menarche; and y to menstrual cycle regularity (<1, 1–2, 3–4, ≥5, never).