Overweight prevention strategies in preschool children

Introduction

During the last several decades, the prevalence of childhood overweight and obesity achieved an alarming rate (1–3). It is also affecting more and more children in the first decade of life. Recent American data indicate that 25.5% of children aged 2 to 5 years had a BMI between 85–94^th percentile, and 12.6% had a BMI greater than 95^th percentile (4). Longitudinal study based on data from National Institute of Child Health showed high ratio of obesity persistence for preschool period into adolescence (5). Children who were overweight in preschool period had 5 times higher risk being overweight at the age of 12 years and 60% of children who were overweight at any time during the preschool period were overweight at the age of 12 years. Childhood obesity is associated with many health complications, such as all the metabolic syndrome components, sleep apnea syndrome and psychological problems (6). Furthermore, being an obese child means to have a significantly higher risk to become an obese adult with all the consequences of the problem (7).

Determinants and risk factors for obesity development in early age

To be able to provide effective prevention strategies for the overweight in preschool children, the identification of potential determinants and risk factors of obesity developments at this age is needed.

The first important period is perinatal life. It is well accepted that breast-feeding has beneficial effect on infants’ health. Meta-analysis made by Harder et al. revealed that breast-feeding is significantly related to a lower risk of childhood obesity development and this beneficial effect was feeding-duration dependent (8). There is also evidence that breast-feeding can have a direct preventive effect for metabolic syndrome development in adulthood. Study based on 625 adults showed that persons who were formula fed in the first weeks of their life had higher glucose level in 120 min of oral glucose tolerance test (OGTT) and were at risk for atherogenic lipid profile (higher LDL and lower HDL cholesterol concentration), even if their BMI was within normal limits (9). The recent GENESIS study identified perinatal parameters predisposing children to increased risk of overweight development (10). Children born large for gestational age, exclusively formula fed, delivered from smoking mothers and having overweight fathers had significantly increased likelihood of childhood overweight at 12 months, 1–3 and 3–5 years of age. The first year of life weight gain seems to be very important for later metabolic and anthropometric programming. A longitudinal observation study from infancy until the age of 6 years showed positive BMI relation at 6 years with weight gain from birth to 12 months. Furthermore, in boys high intake of protein in infancy could also be contributed to childhood obesity (11).

Recently, the large cohort study (13,450 children) showed the strongest association of obesity with parental overweight and low SES (socio- economic status). Furthermore, a positive correlation with childhood obesity was observed for both maternal smoking and high weight gain during pregnancy. High birth weigh, longer screen time, increased intake of high energy food and beverages were other significant risk factors of overweight and obesity. However, long sleep time had beneficial effect on obesity prevention in younger children (3 to 10 years of age) (12). Therefore, low SES associated usually with low educational level families are one of the important target group for the intervention programmes. Some studies showed beneficial effects of the intervention which were independent from family's educational level (13) and were observed even in children from socially deprived areas (14).

The factor which also has to be emphasized, especially in the most developed countries, is the problem of shortening of parental time spent with children. The influence of maternal employment on early childhood overweight was analyzed by Hawkins et al. They found that maternal employment after child's birth was associated with early childhood overweight (15).

The results of study conducted by O'Brien et al. support the idea that childhood overweight has multiple determinants. They found that the main determinant may vary by different age group. In preschoolers it may be the level of mother sensitiveness, but in school children the most important factor is time spent at TV watching after school (16).

The family factor, which seems to be also very important, is the misperception of the children's nutritional status. The study of Harnack et al. performed on the well educated group of parents found that 90.7% parents of obese preschool children classified their child as normal weight. An even higher percentage (94.7%) of overweight children was classified as normal weight by their parents (4). Such low rate of childhood overweight recognition may be the significant problem, because parents may be less preventive against their children becoming obese. The similar results come from focus groups conducted in low-income mothers with children aged 1 to 3 years, which believe that high infant weight is a sign of child health and good parenting (17). That is the reason why parents are particularly important target group for the overweight prevention programme in preschool children. Interesting information about setting of target group in the intervention programme comes from the HIKCUPS study (18). This multicenter randomized controlled trial was designed as three intervention arms: [1] parent-centered nutrition lifestyle programme; [2] child-centered physical activity skill development programme; or [3] both programmes in combination. After 6 and 12 months of intervention all groups improved their dietary intake, without significant differences between groups. The long term follow-up seems to be the essential part of the intervention study design.

Another potential setting for obesity prevention in preschool children is child care system. Kaphingst et al. analyzed obesity-related child care centers (CCC) licensing regulation of US states. They found that despite the regulations in 36 states that required CCC to engage children in at least 60 min of daily outdoor activity time, only 9 states set specific minimum lengths of time that children should stay outdoors each day. Only 12 states had regulations that limited foods of low nutritional value and 8 states regulated time limits on screen time per day or per week in small family child care homes (19).

There exists also the conviction about the important influence of closest environment, especially, the way of spending free time. Neighborhood safety, availability of nearby playground, lack of architectural barriers, etc. have to be the focus of increasing attention in primary prevention efforts. To test this hypothesis, Burdette et al. performed the cross - sectional study in 20 large US cities. Maternal perception of neighbourhood safety was correlated with outdoor playing time and TV viewing. Children, who lived in neighbourhoods that were perceived by their mother as the least safe, watched more TV and were more likely to watch it more than 2 h/day (20).

To summarize, the commonly suggested modifiable strategies are: breast-feeding promotion, limiting television viewing, encouraging physical activity and modifying dietary habits (increasing fruit and vegetable intake, controlling portion size and limiting soft drink consumption) (21,22). Intervention can be child-centered, family-centered (with special emphasis to low SES families) and child care system-centered.

Effectiveness of preventive strategies for preschool children obesity prevalence reduction

Published data about the effectiveness of preventing strategies for childhood obesity development are conflicting.

In the review of controlled trials undertaken to prevent obesity in children and adolescents published by IASO in 2004, there was no study targeted exclusively to preschool children (23). The review published in 2006 (from 21) on international school-based intervention programmes presented two studies arranged for preschool children (21). In the first study, significant improvement in physical activity level (objectively measured by accelerometry) and improvement in motor skills was noted (24). The second intervention designed for improvements of fruit consumption found, that median fruit intake in intervention group was significantly higher (117 g/day vs. 67g/day respectively) (25). The very critical literature review made by Saunders included only six studies which were relevant to prevention of overweight in preschool children. The author indicated that majority of them had several limitations and in overall, their quality was poor. He concluded that there is lack of comprehensive evidence on effective strategies to prevent obesity in early childhood (26). On the other hand, the review published the same year by Campbell and Hesketh was more optimistic. The authors analyzed nine studies focused on children from zero to five years that involved multi- approach interventions and varied in study designs and quality. All of them showed some level of effectiveness of at least one obesity-behaviour in preschool children (27).

These conflicting data confirm the urgent need for the new, well designed preventive strategies in this age group.

Outcome measurements of intervention programme in preschool children

The most important question, in the aspect of overweight prevention in preschool children, is how to assess the effects of the provided programmes. The recent preschool preventive study performed in 64 German kindergartens showed that there were positive behavioural changes in the main outcome measures as prevalence of high fruits and vegetables consumption, in spite of no significant differences in prevalence of overweight and obesity between the intervention and control group after the 6 and 18 months (13). The study conducted by Epstein et al. demonstrated that decreased screen time (TV viewing and computer use) in intervention group had the beneficial and significant influence on both behavioural outcomes (sedentary behaviour and energy intake) and anthropometrical measurements (delta BMI) (28). The similar observations were presented in the Hip-Hop to Health Jr. Study. It was conducted in preschool minority children in US and was effective in reducing subsequent increases in BMI and in lowering the calories intake from saturated fat (29). Very promising data were revealed in the STRIP study, which was a prospective randomized trial started on children at the age of 7 months. Individualized dietary and lifestyle counseling during the first 10 years of life was made. At the age of 10 years, the prevalence of overweight was significantly lower in the intervention group, but, unfortunately, only in girls. STRIP study provides evidence that prevention of obesity in children is feasible, but needs to be started in very early age (30).

On the other side, meta-analysis including 18 studies, based on physical activity intervention, showed no significant beneficial effect if main outcome was BMI changes after interventions which ranged from 6 months to 3 years. The limitation of the majority of the studies included were lack of the objective measures for physical activity. Furthermore, none of the studies measured adherence to the intervention on the individual level. It is quite possible that children with higher BMI may have lower level of adherence (31).

Lack in change in anthropometrical parameters may sometime provoke premature conclusions about ineffectiveness of even well designed interventional studies. A programme consisting of three 30 min sessions of physical activity each week over 24 weeks was conducted for 545 preschool children by Reilly et al (32). Authors did not find the significant reduction of BMI in the intervention group neither after 6 nor after 12 months. Marginal significance (p = 0.05) was found for log percentage time in moderate or vigorous physical activity. However, the significant (p = 0.001) improvement for fundamental movement skills in intervention group was observed. The latter result may be the most important one for the future participation in physical activity or sport, and may be considered as the real positive effect of this intervention.

The aim of the LEAP2 trial was to reduce BMI gain in overweight or mildly obese 5–10 years old children, as well as to improve nutrition and increase physical activity in young children (33). The intervention study was conducted in family practices where children were offered 12 months long programme. Primary care screening followed by brief counseling did not improve neither BMI nor physical activity or nutrition and the costs of the healthcare system were significantly higher in the intervention arm.

It has to be stressed that the expectance of BMI reduction should be a goal of the treatment rather than prevention programmes. Primary prevention programmes should be focused on the longitudinal effects measured by a decreased ratio of new cases incident per year.

In conclusion, prevention of overweight and obesity in younger children is not an easy task, but it could be more rewarding than in the older age group. All the efforts should be made to stop this adverse public health problem from expanding.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.