Table 4.

The joint effect of insomnia symptoms and BMI on risk of fibromyalgia at 11-year follow-up.

BMI	No insomnia symptoms			Insomnia symptoms*
	No. of persons	No. of cases	Multi-adjusted† RR (95% CI)	No. of persons	No. of cases	Multi-adjusted† RR (95% CI)
Normal weight (18.5–24.9 kg/m2)	5818	136	1.00 (reference)	1125	52	1.64 (1.20 to 2.25)
Overweight (25.0–29.9 kg/m2)	4336	138	1.35 (1.07 to 1.70)	889	56	2.35 (1.73 to 3.21)
Obese (≥30 kg/m2)	1621	60	1.55 (1.14 to 2.10)	383	24	2.18 (1.42 to 3.35)

*Participants were classified to have insomnia symptoms if they answered ‘Often/always’ on one of the questions about ‘Problems falling asleep’ and ‘Waking up too early’ or ‘Yes’ on the question about ‘Impaired work ability due to sleep problems’.

†Adjusted for age (20–29, 30–39, 40–49, 50–59, 60–69 and ≥70 years), leisure time physical activity (high activity, moderate activity and low activity), education (primary school, high school, college ≤4 years, college ≥4 years and unknown), The Hospital Anxiety and Depression Scale (no depression and no anxiety, depression and/or anxiety, and unknown) and smoking (never, former, current smoker and unknown).

BMI, body mass index; RR, risk ratio.