Table 2.

Ten-Year Risk of Asthma^a Under Hypothetical Interventions on BMI^b and Moderate-to-Vigorous Physical Activity in Women^c in the Nurses’ Health Study, United States, 1988–1998

Intervention	Asthma Risk, %	95% CI	Population RR	95% CI	Population Risk Difference, %	95% CI	Women Who Received Intervention
							% of Total	% in Each 2-Year Period
Natural course (no intervention)	1.5	1.4, 1.7	1	Referent	0		0	0
Primary interventions
Lose 5% of BMI if BMI >25	1.5	1.4, 1.6	0.96	0.93, 0.99	−0.1	−0.1, −0.01	67	56
Physical activity at least 2.5 hours/weekd	1.5	1.3, 1.7	0.96	0.81, 1.10	−0.1	−0.3, 0.2	97	67
Joint intervention	1.4	1.2, 1.6	0.92	0.78, 1.06	−0.1	−0.3, 0.1	98	77
Secondary interventions
Lose 5% of BMI if BMI >23	1.4	1.3, 1.6	0.94	0.89, 1.00	−0.1	−0.2, −0.01	85	69
Physical activity at least 3.5 hours/weekd	1.4	1.0, 1.8	0.90	0.65, 1.15	−0.2	−0.6, 0.2	98	71
Joint intervention	1.3	0.9, 1.7	0.85	0.62, 1.08	−0.2	−0.6, 0.1	99	85

Abbreviations: BMI, body mass index; CI, confidence interval; RR, risk ratio.

^a Estimated risk in the population using the parametric g-formula to standardize for time-varying covariates (smoking intensity, BMI, menopausal status, postmenopausal hormone use, physical activity), and baseline covariates (age, smoking history prior to 1988, type of nursing, BMI, BMI at 18 years of age, smoking intensity, menopausal status, postmenopausal hormone use, physical activity).

^b Weight (kg)/height (m)².

^c Total of 76,470 women and 1,146 asthma cases representing 746,096 person-years.

^d Equates to 30 minutes/day on 5 days/week.