Finally, an analysis of risk factors for RLS was done using multivariate logistic regression, first with a single model that was adjusted for all factors listed in Table 3. In this model, we observed significant effects of age, sex, and parity among women (data not shown). Because the findings in Figure 1 indicate an increased RLS prevalence until age 60 years, when the number of premenopausal and perimenopausal women has decreased to a minimum, we also explored a potential effect modification of RLS-associated risk factors by age, using a stratified analysis. Results of these more detailed analyses are shown in Table 3. In younger study participants (20-59 years), the OR for RLS increased significantly with age, but not in older individuals. Compared with men, younger women had a more than 2-fold increased OR for RLS, and it remained significantly elevated in older women. In the younger age group, the OR for RLS increased with the number of births among women, following a significant linear trend. In older women, this association was inverse and was not significant. Using nulliparous women instead of men as the reference group still revealed a dose-response relationship in the younger age group, with only slightly reduced ORs (women with 1 child, 1.54; 2 children, 2.37; and ≥3 children, 2.79; P = .002 for trend). In older women, the inverse, nonsignificant relationship remained unchanged. Further risk factor evaluation revealed that low educational attainment was significantly related to RLS status. This effect was stronger in participants aged 20 to 59 years. Separate analyses in men and women showed that this relationship was found in both sexes. Because low educational attainment might be related to the number of births among women, we additionally analyzed this association, stratified by level of educational attainment. Within each of the 3 levels of educational attainment, we observed an increase in risk of RLS associated with increasing number of children, compared with nulliparous women (OR, 1.40, P = .06 for trend across categories of parity in women with primary school education; OR, 1.36, P = .04 for secondary school education; and OR, 1.67, P = .10 for tertiary school education). The risk associated with low educational attainment was also not explained by higher rates of comorbidities among those participants with a primary school education. Restricting the analysis to individuals without diabetes mellitus, reduced renal function, anemia, or thyroid disease revealed the same linear increase in risk associated with parity and a higher risk for those with low educational attainment. The presence of diabetes mellitus was associated with RLS in older age groups only. Ex-smokers and current smokers had higher risks for RLS, reaching statistical significance in the latter group aged 20 to 59 years.