Table 3.

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

Intervention by Smoking Status	No.	Asthma Risk, %	95% CI	Population RR	95% CI	Population Risk Difference, %	95% CI
Never smokersc	34,026
Lose 5% of BMI if BMI >25		1.4	1.3, 1.6	0.98d	0.94, 1.03	−0.03e	−0.1, 0.04
Physical activity ≥2.5 hours/week		1.5	1.2, 1.9	1.05f	0.82, 1.32	0.1g	−0.3, 0.5
Joint intervention		1.5	1.2, 1.9	1.04h	0.79, 1.30	0.1i	−0.3, 0.5
Former smokersj	26,371
Lose 5% of BMI if BMI >25		1.5	1.4, 1.7	0.95	0.90, 1.00	−0.1	−0.2, 0
Physical activity ≥2.5 hours/week		1.6	1.2, 2.0	0.96	0.76, 1.21	−0.1	−0.4, 0.3
Joint intervention		1.5	1.2, 1.9	0.91	0.71, 1.16	−0.2	−0.5, 0.03
Active smokersk	16,073
Lose 5% of BMI if BMI >25		1.5	1.3, 1.7	0.94	0.89, 1.01	−0.1	−0.2, 0.01
Physical activity ≥2.5 hours/week		1.1	0.7, 1.6	0.71	0.47, 1.02	−0.5	−0.9, 0.3
Joint intervention		1.0	0.7, 1.5	0.67	0.44, 0.98	−0.5	−0.9, 0.04

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 There were 485 asthma cases among never smokers.

^d P for heterogeneity across smoking groups = 0.512.

^e P for heterogeneity across smoking groups = 0.395.

^f P for heterogeneity across smoking groups = 0.183.

^g P for heterogeneity across smoking groups = 0.264.

^h P for heterogeneity across smoking groups = 0.142.

ⁱ P for heterogeneity across smoking groups = 0.126.

^j There were 417 asthma cases among former smokers.

^k There were 244 asthma cases among current smokers.