Sex differences in overweight, obesity and environmental factors among 7-year-olds in Bulgaria

Background

Childhood obesity is a major public health concern. Evidence indicates sex differences in prevalence and behaviours, but data in early school age are limited. This study examines sex differences in overweight, obesity and selected environmental factors among 7-year-olds in Bulgaria.

Methods

In 2023, a nationally representative cross-sectional survey of first-grade children was conducted in Bulgaria within the Round 6 of WHO European Childhood Obesity Surveillance Initiative (COSI). Height and weight were measured using standardized protocols. Overweight, obesity and severe obesity were defined using BMI-for-age (WHO Reference 2007). Parental questionnaires captured information on diet, physical activity, screen time and sleep. Sex differences were assessed with design-adjusted Wald/χ² tests (p < 0.05).

Results

Among 3 110 surveyed children (1 556 boys; 1 554 girls), overweight prevalence did not differ by sex (32.6% boys vs 33.0% girls; p = 0.846). Obesity was higher in boys (16.7% vs 13.7%; p = 0.031) and severe obesity was nearly twofold higher (6.8% vs 3.3%; p < 0.001). Breakfast consumption was high among all respondents (∼86%). Daily fruit consumption was more frequent in girls (57.5% vs 50.0%; p = 0.001), while vegetable intake was similar. Boys showed higher prevalence of sugar-sweetened soft drinks consumption (19.8% vs 15.7%; p = 0.066) and ≥2 h/day screen time (35.7% vs 31.2%; p = 0.060), and more often reported >1 h/day active play (96.6% vs 93.7%; p = 0.003). Sleep duration did not differ.

Conclusions

While overweight is similar, obesity—particularly severe—is more prevalent in boys. Early prevention should incorporate sex-sensitive strategies targeting diet quality and sedentary behaviours. Continuous surveillance through systems such as COSI is essential for targeted action.

Key messages

• Obesity and severe obesity are higher in boys than girls, despite similar overweight prevalence.

• Sex-specific behaviours support the need for targeted early prevention.