Table 2.

Age-stratified multivariable adjusted hazards ratios^a (HRs) and 95% confidence intervals (CIs) for the associations between physical activity and relative timing of natural menopause among 97,945 participants in the California Teachers Study, established 1995–1996

	Person-Years	No. with Natural Menopause	HR^a,^b	95% CI	p-trend^c
Long-term combined physical activity (hours/week/year)
Quartile 1 (< 1.61)	1,137,311	10,590	1.00	Reference
Quartile 2 (1.61–3.449)	1,090,225	7,769	0.97	0.94–1.00
Quartile 3 (3.45–6.239)	1,072,019	6,764	0.96	0.93–0.99
Quartile 4 (≥ 6.24)	1,054,036	6,484	0.95	0.92–0.98	0.005
Race/ethnicity
Non-Hispanic White	3,776,357	28,259	1.00	Reference
African American	110,685	861	0.97	0.91–1.04
Hispanic	184,695	747	1.17	1.09–1.26
Asian	164,311	989	1.00	0.94–1.06
Other^d	117,543	751	0.98	0.91–1.06
Smoking status^e
Never	2,965,083	18,852	1.00	Reference
Former-light smoker	458,157	3,209	0.96	0.92–0.99
Former-heavy smoker	479,293	4,138	0.93	0.90–0.96
Current-light smoker	200,089	2,136	1.68	1.60–1.75
Current-heavy smoker	205,379	2,847	1.38	1.33–1.44
BMI at age 18 years (kg/m²)
<20.00	1,397,576	9,920	1.00	Reference
20.00–24.99	2,332,413	16,901	0.97	0.95–1.00
25.00–29.99	324,549	2,161	0.95	0.91–1.00
≥30.00	116,707	702	0.88	0.81–0.95	0.0003
Age at menarche (in years)
≤ 10	303,067	2,068	1.01	0.96–1.06
11–12	1,847,919	13,194	1.00	Reference
13–14	1,834,750	13,662	0.99	0.97–1.01
≥ 15	345,748	2,594	0.91	0.87–0.95	0.0003
Age at first full-term pregnancy (in years) and parity
<29, 2+ full-term pregnancies	1,889,929	16,628	1.00	Reference
<29, 1 full-term pregnancy	300,427	2,068	1.09	1.04–1.14
≥ 29, 2+ full-term pregnancies	606,456	3,885	1.10	1.06–1.14
≥ 29, 1 full-term pregnancy	373,387	2,039	1.18	1.13–1.24
Ever pregnant, no full-term pregnancy	262,255	1,157	1.21	1.14–1.28
Never pregnant	880,014	5,594	1.26	1.22–1.30

Hazard ratios are adjusted for all factors shown in table and stratified by age in years at cohort entry.

A hazard ratio less than 1.00 indicates that among members of each age group, the ‘risk’ of experiencing a natural menopause was lower in the exposed vs. referent group (e.g. natural menopause occurred later in the exposed vs. referent group.) Conversely, a hazard ratio greater than 1.00 indicates that among member of each age group, the ‘risk’ of experiencing a natural menopause was higher in the exposed vs. referent group (e.g. natural menopause occurred earlier in the exposed vs. referent group.)

Multivariable p values for trend were calculated using the continuous variables for physical activity, BMI at age 18; and were calculated using the midpoints of the categories shown above for age at menarche. Participants with missing or unknown data for a variable were considered as a separate category in models producing hazard ratios (the results for which are not shown) and deleted from the appropriate model when assessing the p for trend for that variable.

Other race/ethnicity includes Native American participants, and participants of mixed, other or undeclared racial/ethnic status.

Never smokers include 2,277 participants who started smoking at or after the age at menopause. Former or current smokers were dichotomized as light or heavy smokers based on median total pack-years (4.375 for former smokers, 18 for current smokers).