The research team recruited 760 children through primary health care centres in the Lisbon Metropolitan Area and focused their analysis on the 453 children aged at least four years whose caregivers completed a valid Strengths and Difficulties Questionnaire, or SDQ. This instrument, which is used extensively in developmental epidemiology, asks parents to rate their child across domains including emotional symptoms, conduct problems, hyperactivity, peer relationship problems and prosocial behaviour. The researchers defined early mental health difficulties as a Total Difficulties score of 14 or higher, the threshold that places a child in the borderline or abnormal range. Children were classified as having an immigrant background if the child or at least one parent had been born outside the European Union, a definition that captures a broad swath of families in the Lisbon region.

The headline finding is stark: nearly a quarter of the screened children exhibited difficulties at a level that would typically warrant clinical attention or further assessment. But the study’s most valuable contribution lies in its multivariable logistic regression analysis, conducted on the 417 children with complete data, which teased apart which social, family and behavioural factors were independently associated with elevated scores. Three factors stood out after adjustment for the others: household income, family structure and sports participation.

Income emerged as a powerful correlate. Children living in households earning between roughly 750 and 1,500 euros per month had more than double the adjusted odds of scoring in the borderline or abnormal range compared with children from households earning above 1,500 euros per month, with an adjusted odds ratio of 2.10 and a 95 percent confidence interval of 1.13 to 3.90. This gradient is consistent with a substantial body of international literature linking economic hardship to early childhood psychopathology, but the Portuguese data are notable because they come from a community sample recruited through routine primary care rather than from clinical referrals, meaning the findings reflect the general preschool population rather than children already in treatment.

Family structure also mattered. Children living in extended families or other non-nuclear arrangements had 82 percent higher adjusted odds of elevated Total Difficulties scores than children in nuclear households, with an adjusted odds ratio of 1.82 and a confidence interval of 1.02 to 3.26. The authors are careful to note that this association does not imply that extended families are inherently harmful; such households may, for instance, be more common among families navigating economic precarity, housing constraints or the demands of migration, and the cross-sectional design cannot disentangle these overlapping influences. What the finding does suggest is that the composition and circumstances of a child’s household carry measurable weight in early mental health screening.

The strongest behavioural association involved physical activity. Children who did not participate in sports had nearly three times the adjusted odds of elevated difficulties compared with their peers who did, with an adjusted odds ratio of 2.80 and a confidence interval of 1.59 to 4.94. This result was the most robust across the study’s two analytical approaches. In addition to the dichotomised logistic regression, the researchers ran a negative binomial model on the undichotomised SDQ Total Difficulties score, a technique suited to count-like outcome data that preserves the full granularity of the scale. That full-score analysis supported the sports participation association, while the estimates for income and family structure were less conclusive, suggesting those relationships warrant further scrutiny in larger or longitudinal samples.

A central question driving the study was whether children with an immigrant background face a heightened burden of early mental health difficulties. The descriptive data showed real disparities: immigrant-background children experienced greater socioeconomic disadvantage, higher screen exposure and lower sports participation, and they more often scored in the abnormal range for peer relationship problems, at 12.5 percent versus 5.7 percent among children without an immigrant background. Yet when the researchers adjusted for socioeconomic and family circumstances, the association between immigrant background and overall difficulties largely disappeared, with an adjusted odds ratio of 1.09 and a confidence interval spanning 0.66 to 1.79. In other words, the apparent gap appears to be explained largely by the social and economic conditions in which these children are growing up rather than by their migrant status itself.

This pattern, often described in social epidemiology as attenuation through adjustment, carries significant policy implications. If the elevated risk among immigrant-background children flows primarily through poverty, family arrangements and daily routines, then interventions targeting those upstream conditions could benefit all vulnerable children regardless of origin. The authors argue that primary care and community services are well positioned to help families access appropriate support, since the study’s recruitment through primary health care centres demonstrates that these settings already reach the families in question. Screening embedded in routine paediatric visits, combined with referral pathways to mental health and social services, could identify children during the developmental window when intervention is most effective.

The study’s methodology reflects standard practice in observational epidemiology. The researchers followed the STROBE reporting guidelines for cross-sectional studies, assessed multicollinearity among predictors using variance inflation factors, and obtained ethics approval from the Research Ethics Committee of the Regional Health Administration of Lisboa e Vale do Tejo, with written informed consent from all participating parents and caregivers. The work was funded by the Portuguese Foundation for Science and Technology under grant PTDC/SAU-SER/4664/2020, with additional support through the Global Health and Tropical Medicine research unit and the REAL associated laboratory. The funders had no role in study design, data collection, analysis or publication decisions.

Like all cross-sectional studies, this one has inherent limits. The data capture a single moment in time, so the observed associations cannot establish whether low income, non-nuclear family structures or lack of sports participation cause mental health difficulties, or whether families facing other challenges are simply more likely to experience all of these conditions together. Parent-reported questionnaires, while validated and widely used, reflect caregiver perception rather than clinical diagnosis. The authors themselves call for longitudinal and intervention studies to clarify these relationships and assess whether modifying daily routines, such as increasing sports participation, could have preventive effects. Still, the message for public health is clear and actionable: early mental health inequalities are already visible at age four, they track closely with economic and family circumstances, and the primary care system is a viable front line for finding and supporting the children who need help most.

Subject of Research: Social, family and health behaviour correlates of early mental health difficulties among preschool children in Portugal

Article Title: Early mental health inequalities among preschool children in Portugal: a cross-sectional study of social, family and health behaviour correlates

Article References: Gonçalves, R., Dias, S., & Martins, M. R. O. (2026). Early mental health inequalities among preschool children in Portugal: a cross-sectional study of social, family and health behaviour correlates. BMC Public Health. https://doi.org/10.1186/s12889-026-29767-y

Image Credits: AI Generated

DOI: 10.1186/s12889-026-29767-y

Keywords: preschool children, mental health difficulties, health inequalities, social determinants of health, Strengths and Difficulties Questionnaire, immigrant background, sports participation, household income, family structure, primary health care, Portugal, cross-sectional study