Early nutrition and overweight

A number of studies have examined early nutrition, including breastfeeding, and associations with obesity with conflicting results⁽ Reference Watson ^{1 –} Reference Auld ^{9 )}. Differences in findings are likely due to a lack of control for confounding variables, small sample size, socioeconomic status and other differences such as subject age at time of measurement and family structure^{( 10 )}. Some studies have found a positive, dose-dependent association between breastfeeding and weight status⁽ Reference Kramer ^{11 –} Reference Harder, Bergmann and Kallischnigg ^{13 )}, while others have reported a nonlinear positive response⁽ Reference von Kries, Doletzko and Sauerwald ^{14 –} Reference Gillman, Rifas-Shiman and Camargo ^{16 )}. On the contrary, other studies have demonstrated little or no protective association between breastfeeding and overweight; including a longitudinal study of infant feeding and obesity which found that exclusive breastfeeding was not related to being overweight or obese during adult life⁽ Reference Toschke, Martin and von Kries ^{17 –} Reference Michels, Willett and Graubard ^{21 )}. Similarly, a systematic analysis conducted by the WHO⁽ Reference Horta, Bahl and Martines ^{22 )} and a systematic review of the literature found that after adjustment for maternal overweight the effect of breastfeeding was eliminated⁽ Reference Owen, Martin and Whincup ^{23 )}. It has been suggested that breastfeeding alone does not protect children from overweight but rather other healthy lifestyle habits or other social advantages of mothers who chose to breastfeed^{( 10 )}. While the relationship between breastfeeding and obesity has not been fully elucidated, it is recommended by the WHO and Cochrane Review that children are exclusively breastfed for 6 months due to other known benefits and this is supported by the ESPGHAN Committee on Nutrition, which recommended children be exclusively breastfed for about 6 months⁽ Reference Agostoni, Braegger and Decsi ^{24 –} Reference Kramer and Kakuma ^{26 )}.

Recently, our group examined exposure to exclusive breastfeeding and overweight in the Identification and prevention of Dietary- and lifestyle-induced health EFfects In Children and infantS (IDEFICS) study. IDEFICS is a multi-centre European study involving eight countries: Italy, Estonia, Cyprus, Belgium, Sweden, Hungary, Germany and Spain. Community-based survey centres in each of the participating countries collected information when children were age 2–9 years from September 2007 until June 2008 at survey centres that cannot be considered country representative. In total, over 16 000 children participated in IDEFICS⁽ Reference Ahrens, Bammann and Siani ^{27 )}. From the IDEFICS population, children were included in the first study if their exposure to exclusive breastfeeding could be defined⁽ Reference Hunsberger, Lanfer and Reeske ^{28 )}. After exclusions, the total sample size in our exclusive breastfeeding study was 14 726 children with sample sizes across countries ranging from 1399 in Spain to 2431 in Hungary.

Characteristics by survey centre have been previously published in detail⁽ Reference Hunsberger, Lanfer and Reeske ^{28 )}. In brief, the prevalence of overweight was 19·4 %, ranging from a high of 42·3 % in Italy to a low of 8·3 % in Belgium at baseline data collection in IDEFICS. Children were aged 2–9 years at the baseline survey with a mean age of 6 years and were analysed in two age groups of similar size, pre-school age (2 to <6 years) and school age (6–9 years). The gender distribution is nearly equal across survey centres.

When all centres are combined, <20 % of IDEFICS children were never exclusively breastfed for at least some period although there are distinct differences across the countries. For example, in Belgium 46·1 % of the children were never breastfed whereas in Estonia only 9·9 % of the children were never breastfed⁽ Reference Hunsberger, Lanfer and Reeske ^{28 )}. The mean duration of exclusive breastfeeding was 3·2 months across all survey centres.

Exclusive breastfeeding and overweight/obesity combined were examined with adjustment for survey country, child age, sex and birth weight, included household income, maternal education, maternal overweight/obesity, single or dual parent family structure, the presence of one or more foreign born parents, and tobacco use during pregnancy. In our fully adjusted model, breastfeeding exclusively for 4–6 months was protective of overweight (including obesity) when compared with children never exclusively breastfed (OR 0·73, 95 % CI 0·63, 0·85). In addition, exclusive breastfeeding for 6 months offered slightly more protection than 4 and 5 months combined (OR 0·71, 95 % CI 0·58, 0·85). Findings were consistent between boys and girls. The associations could not be explained by socioeconomic characteristics or maternal overweight.

Since the use of BMI as an appropriate means of assessing childhood weight-related health risks is not clear⁽ Reference Flegal and Ogden ^{29 )}, our group further assessed overweight/obesity with skinfold measures and waist∶height ratio. A logistic regression model and generalised linear regression model respectfully demonstrated waist∶height ratio and per cent body fatness assessed by skinfold measure both agreed with our initial logistic regression findings and support our use of BMI as a binary outcome representing overweight children. Comparing obesity prevalence by BMI categories with waist : height ratio, there was 86·19 % agreement among normal weight children and 67·25 % among overweight/obese. Agreement by skinfold assessment was slightly greater, in the normal weight BMI category there was 86·9 % agreement and in the overweight/obese 75·95 % agreement.

More recently, a novel analysis of variables predictive of adult obesity was carried out by the Foresight Obesity System Map group; a project of the UK government think-tank Foresight⁽ Reference Butland, Jebb and Kopelman ^{30 )}. A two-way framework of past/fixed and present/modifiable factors are presented for a sample (n 11 752)⁽ Reference Potter and Ulijaszek ^{31 )}. Breastfeeding for any amount of time and normal birth weight were included as positive conditioning factors or factors that occurred in the past that cannot be changed⁽ Reference Potter and Ulijaszek ^{31 )}. Individuals identified in the highest risk category at age 11 years were approximately two times as likely to become overweight by age 23 years and obese in their 30s and 40s as opposed to their low-risk peers⁽ Reference Potter and Ulijaszek ^{31 )}. These findings support the protective role of breastfeeding. Further, a systematic literature review that included sixty papers concluded the evidence of a protective dose/duration effect of breastfeeding against overweight and obesity in childhood and adolescence is convincing⁽ Reference Hörnell, Lagström and Lande ^{32 )}. The authors also concluded that there is probable evidence that exclusive breastfeeding for longer than 4 months is associated with slower weight gain from 6 to 12 months and may be the reason behind the reduced risk of later overweight and obesity⁽ Reference Hörnell, Lagström and Lande ^{32 )}. In light of these findings, there is good evidence that breastfeeding is protective against the development of overweight later in life.

Family structure and overweight

In addition to early nutrition, the role of family structure may also have important implications for future childhood overweight and obesity. However, the role of family structure in the development of obesity is not well elucidated. Singleton status was identified as a risk factor for obesity in one Norwegian population study⁽ Reference Júlíusson, Eide and Roelants ^{33 )}, and the research suggests that first-born children receive more ‘quality time’ per day than those born into a household with a sibling⁽ Reference Price ^{34 )}. Furthermore, the influence of social networks is likely an important component of overweight development⁽ Reference Christakis and Fowler ^{8 ,} Reference Auld ^{9 )}.

Our group investigated the role of family structure and overweight among the IDEFICS children across eight European countries. In this study, 12 720 children were included based upon completeness of family structure data⁽ Reference Hunsberger, Formisano and Reisch ^{35 )}. All survey centres obtained ethics approval from their respective authority. Parents or legal guardians provided written informed consent on behalf of their children for data collection and specimen collection and children gave oral consent. Detailed information about IDEFICS survey protocol has been previously published⁽ Reference Ahrens, Bammann and Siani ^{27 )} as have the detailed methods this study⁽ Reference Hunsberger, Formisano and Reisch ^{35 )}.

While breastfeeding is protective of overweight, being an only child is not. IDEFICS children without siblings were more likely (OR 1·52, 95 % CI 1·34, 1·72) to be overweight than their peers with siblings when controlling for factors related to childhood overweight (parental education, parental weight, maternal age, child's age, birth weight and gender) and for survey country. In fact, the longer a child remains an only child, the stronger the association with overweight. As previously reported by our group, among older singletons the association with overweight (OR 1·70, 95 % CI 1·44, 2·01) was greater than for younger singletons (OR 1·32, 95 % CI 1·10, 1·60)⁽ Reference Hörnell, Lagström and Lande ^{32 )}. The potential behavioural mediators examined (playtime outdoors, screen time/d, propensity to consume sugar or fat, parental attitudes towards food rewards and television in the child's bedroom) did not attenuate the relationship between only children and overweight with associated OR ranging from 1·51 to 1·58 when each mediator was explored individually and in combination. In a sensitivity analysis, having a sibling was protective regardless of birth order (twins or those with older siblings v. only younger sibling) when only children were compared with those with siblings. Additional analyses suggested that children who have always had a sibling were slightly more protected from overweight than those that were previously a singleton until the arrival of a younger sibling but this finding was not statistically significant.

New findings from our group further demonstrate only children are at increased risk for overweight. Among the IDEFICS sample, children with the greatest number of siblings had the lowest BMI z-scores in cross-sectional analyses and over a 2-year follow-up period the risk of incidence of overweight/obesity was significantly lowered by the greater the number of siblings living in the household⁽ Reference Formisano, Hunsberger and Bammann ^{36 )}.

Limited research has examined the role of siblings in the home. Other studies have focused on family structure but have placed emphasis on the adults in the home rather than siblings. For example, a recent study in South Korea examined the relationship between child weight status by household structure but did not report on sibling status⁽ Reference Eidsdóttir, Kristjánsson and Sigfúsdóttir ^{37 )}. In contrast to the limited studies that have found a relationship between family structure and childhood weight status, an Icelandic research group reported no association between family structure and the prevalence of overweight and obesity among 16- to 20-year-old adolescents⁽ Reference Lee, Duffey and Kim ^{38 )}.