Introduction

The variation in height, weight and body mass index (BMI) is influenced by genetic and environmental factors (Ulijaszek et al., Reference Ulijaszek, Johnston and Preece1998; Susanne et al., Reference Susanne, Rebato and Hauspie2000; Haas & Campirano, Reference Haas and Campirano2006; Walker et al., Reference Walker, Gurven, Hill, Migliano, Chagnon and De Souza2006; Jakimaviciene & Tutkuviene, Reference Jakimaviciene and Tutkuviene2007a; Hermanussen, Reference Hermanussen2013). Though height, weight and BMI are under the regulation of inherited mechanisms, environmental factors may change the growth process and even cause growth retardation or acceleration (Cameron & Bogin, Reference Cameron and Bogin2012). Many factors that might be associated with growth have been explored, and models of their interactions created (Harrison et al., Reference Harrison, Bost, McBride, Donovan, Grigsby-Toussaint and Kim2011). These factors can be divided into several categories: ethnic, social, economic, cultural, physical and the others. The interaction of the aforementioned factors is very complex and not fully understood. In recent years, studies on factors related to growth have had contradictory results: some authors state that genetic factors have the bigger impact on child growth (Hur et al., Reference Hur, Kaprio, Iacono, Boomsma, McGue and Silventoinen2008; Dubois et al., Reference Dubois, Kyvik, Girard, Tatone-Tokuda, Pérusse and Hjelmborg2012), and others argue that environmental ones do (Siniarska-Wolanska et al., Reference Siniarska-Wolanska, Golab and Koziel2010).

In comparison with other environmental factors, socioeconomic factors have recently been assumed to have the greatest impact on child growth (Tanner, Reference Tanner1990; Ulijaszek et al., Reference Ulijaszek, Johnston and Preece1998; Susanne et al., Reference Susanne, Rebato and Hauspie2000; Roche & Sun, Reference Roche and Sun2003; Bodzsar & Susanne, Reference Bodzsar and Susanne2004; Haas & Campirano, Reference Haas and Campirano2006; Walker et al., Reference Walker, Gurven, Hill, Migliano, Chagnon and De Souza2006). This big group of factors includes levels of maternal and paternal education, parents’ occupation, family income and dietary patterns. It is known that socioeconomic factors have different relations with child height and weight. The socioeconomic status of the family and the child’s height are in a direct positive relationship (children who grow up in families with high socioeconomic status are taller) (Cameron & Bogin, Reference Cameron and Bogin2012). The relationship between socioeconomic factors and child weight and BMI is more complex. It has been shown that people in poor countries (both adults and children) living under good socioeconomic conditions have a greater risk of being overweight or obese (Wang, Reference Wang2001; Ulijaszek & Lofink, Reference Ulijaszek and Lofink2006; Wang & Lobstein, Reference Wang and Lobstein2006; Ulijaszek, Reference Ulijaszek2007; Navti et al., Reference Navti, Ferrari, Tange, Bechtold-Dalla Pozza and Parhofer2014). This phenomenon has been explained by the fact that in poor countries high body weight is often associated with greater wealth (Ulijaszek et al., Reference Ulijaszek, Johnston and Preece1998). For a long time, the prevalence of overweight and obesity in poorer countries has been lower than in developed regions. However, recent studies from developing countries have shown an increase in overweight and obesity among children and adolescents (Reddy et al., Reference Reddy, Resnicow, James, Funani, Kambaran and Omardien2012), especially in large cities (Zhang et al., Reference Zhang, Guo, Tu, Kiess, Sun and Li2012). Still, obesity problems are more typical of families of low socioeconomic status (Ulijaszek et al., Reference Ulijaszek, Johnston and Preece1998; Klein-Platar et al., Reference Klein-Platar, Wagner, Haan, Arveiler, Schlienger and Simon2003; Power et al., Reference Power, Manor and Matthews2003; Ulijaszek & Lofink, Reference Ulijaszek and Lofink2006; Wang & Lobstein, Reference Wang and Lobstein2006; Moschonis et al., Reference Moschonis, Tanagra, Vandorou, Kyriakou, Dede and Siatitsa2010).

Auxologists agree that such factors as parental occupation, level of education and ‘intelligence’ (which lead to understanding how a child should be raised) are very important, but are very difficult to measure. Some authors stated that occupation and level of education of both parents have had an impact on their child’s growth (Bielicki et al., Reference Bielicki, Szklarska, Koziel and Ulijaszek2005); others, that a child’s growth correlates more with either the father’s or mother’s educational level (Delpeuch et al., Reference Delpeuch, Traissac, Martin-Prével, Massamba and Maire2000; Heineck, Reference Heineck2006; Hui et al., Reference Hui, Leung, Cowling, Lam and Schooling2008; Bornstein & Bradley, Reference Bornstein and Bradley2014). In some studies the association between children’s physical indices and parental educational level was neglected and family income was named as the most important factor (Joshi et al., Reference Joshi, Rikimaru and Sharada2005; Gultekin et al., Reference Gultekin, Hauspie, Susanne and Gulec2006; Turan et al., Reference Turan, Bereket, Furman, Omar, Berber and Ozen2007). Even occupation of grandparents has been found to play an important role (Young et al., Reference Young, Relethford and Crawford2008). In developed countries, father’s occupation has been related to bigger body size indices of the child (Brisbois et al., Reference Brisbois, Farmer and McCargar2012), whereas in developing countries maternal educational level has been found to be more important (Leroy et al., Reference Leroy, Habicht, Gonzalez de Cossio and Ruel2014). However, in countries with the best economies and social guarantees (e.g. in Scandinavia), maternal educational level seems to play the most important role: in this case, income does not matter (in such countries even unqualified labourers earn enough), but an understanding how to raise children matters more, and this might be called ‘intelligence’ (Mortensen et al., Reference Mortensen, Diderichsen, Arntzen, Gissler, Cnattingius and Schnor2008).

Differences in the growth of children from urban and rural regions have been described for many years (Ulijaszek et al., Reference Ulijaszek, Johnston and Preece1998; Paciorek et al., Reference Paciorek, Stevens, Finucane and Ezzati2013; Pomeroy et al., Reference Pomeroy, Stock, Stanojevic, Miranda, Cole and Wells2014). Urban children have been found to demonstrate ‘better growth’ (appear to be taller) than their rural counterparts; however, this rule is not as obvious as it appears. Three decades ago, it was noticed that in developed countries rural children were taller than their urban peers – they benefited from all the achievements of civilization but at the same time did not face the ‘misuses’ of urbanization (Rona, Reference Rona1981). Therefore, it seems that urban and rural differences in growth may be explained by the impact of socioeconomic factors (Oyhenart et al., Reference Oyhenart, Castro, Forte, Sicre, Quintero and Luis2008; Bjerregaard & Greenland Population Study Group, Reference Bjerregaard2010).

It has long been known that birth order is associated with the size of newborns (Cesnys, Reference Cesnys1970). Moreover, first-born children remain taller, even at the end of growth (Myrskyla et al., Reference Myrskyla, Silventoinen, Jelenkovic, Tynelius and Rasmussen2013). Only-children have been reported to have an increased risk of becoming overweight or obese (Wang et al., Reference Wang, Sekine, Chen, Kanayama, Yamagami and Kagamimori2007). Birth order is inversely related to BMI (Jelenkovic et al., Reference Jelenkovic, Silventoinen, Tynelius, Myrskylä and Rasmussen2013); however, positive (Fredriks et al., Reference Fredriks, van Buuren, Wit and Verloove-Vanhorick2000) and non-significant (Howe et al., Reference Howe, Hallal, Matijasevich, Wells, Santos and Barros2014) relationships have also been reported.

Ethnic and cultural growth factors are also very important. Though ethnic factors are understood as genetic growth factors, ethnicity is also related to particular cultural factors: people of different ethnicities live together in one country, but they have different traditions and religious views (i.e. different lifestyles, family patterns, reproductive age, dietary habits, etc.). There is an opinion that due to the globalization process, the associations between body size and cultural factors might even disappear in the future (Roche & Sun, Reference Roche and Sun2003). At present, ethnic and cultural factors are still considered to be associated with body size. It is often stated that immigrants have the highest chance of being overweight or obese, possibly due to their lower socioeconomic status (Will et al., Reference Will, Zeeb and Baune2005; Kirchengast & Schober, Reference Kirchengast and Schober2006; Kilaf & Kirchengast, Reference Kilaf and Kirchengast2011), though this theory does not explain all the differences in body composition. The children of immigrants have a higher risk of overweight and obesity even in comparison to the natives from the same socioeconomic stratum (Saxena et al., Reference Saxena, Ambler, Cole and Majeed2004; Will et al., Reference Will, Zeeb and Baune2005; Kirchengast & Schober, Reference Kirchengast and Schober2006; Harding et al., Reference Harding, Teyhan, Maynard and Criuckshank2008). Thus their risk of suffering from arterial hypertension, coronary heart disease and type II diabetes mellitus is also higher (Ujcic-Voortman et al., Reference Ujcic-Voortman, Baan, Seidell and Verhoeff2012). These diseases shorten the lifespan; moreover, their treatment is very costly for the state. A recent study in Lithuania investigated the growth of preschool children from different ethnic groups (Jakimaviciene & Tutkuviene, Reference Jakimaviciene and Tutkuviene2007b; Tutkuviene et al., Reference Tutkuviene, Morkuniene, Bartkute and Drazdiene2011). However, in Lithuania no research on the growth of children of different ethnicities from birth up to the end of the growth period has ever been performed.

The secular trend of physical status is the mirror of socioeconomic conditions. Over the past century, an acceleration in body height has been observed worldwide (Hermanussen, Reference Hermanussen2013). During the last decades this acceleration has stabilized in Lithuania: the heights of children and adolescents are now almost the same as they were 10–15 years ago. Recently, auxological data from other countries have shown that stabilization in height has been followed by an increase in the prevalence of overweight and obesity in children (Gohlke & Woelfle, Reference Gohlke and Woelfle2009). Certain factors associated with the acceleration in height (for example, changes in dietary patterns) are thought to promote a later disproportionate increase in BMI (Tutkuviene et al., Reference Tutkuviene, Morkuniene, Bartkute and Drazdiene2011). In recent times, the aforementioned processes have emerged in Lithuania, and the prevalence of overweight and obesity in children has just started to rise (Suchomlinov et al., Reference Suchomlinov, Cerskus, Kolosov, Rakita and Tutkuviene2014). It is therefore crucial that this transitional period in children’s growth in relation to changing lifestyles and socioeconomic situation in Lithuania is studied.