Hawkins A review of risk factors in preschool children1
A review of risk factors for overweight in preschool
children: a policy perspective
Running head: A review of risk factors in preschool children
Type of manuscript: Review article
Summer Sherburne Hawkins, Catherine Law
Centre for Paediatric Epidemiology and Biostatistics, Institute of Child Health,
30 Guilford Street, London WC1N 1EH UK
Address all correspondence to:
Summer Sherburne Hawkins
Centre for Paediatric Epidemiology and Biostatistics
Institute of Child Health,
30 Guilford Street
London WC1N 1EH
Phone +44 207 905 2790
Fax +44 207 905 2381
Both authors have no conflicts of interest to declare.
Word count for abstract: 152
Word count for manuscript (text and references): 10008
Text (excluding references): 6474
References: 154 (59 studies reviewed)
Hawkins A review of risk factors in preschool children2
An increasing number of preschool children are becoming overweight. Although many
risk factors have been identified for school-age children, less is known about this young
age group. Ecological models have been developed to illustrate how individual
characteristics, family characteristics, community-level factors, and policies may
influence weight gain. We used this model to review factors that influence overweight in
children, aged six months to five years, which are amenable to policy intervention in
resource-rich countries. We found strong evidence for a direct association between
childhood overweight and maternal prepregnancy body size, maternal smoking during
pregnancy, and children’s television/media use; strong evidence for an inverse
relationship between breastfeeding and overweight and moderate evidence for children’s
physical activity. There was limited research on community-level factors, policies and
interventions. Future policies and interventions should be subject to evaluation and aim to
support parents and young children to develop health-related behaviours that may prevent
early childhood overweight.
Key words: body mass index, obesity, infant, preschool child, review, public policy
Hawkins A review of risk factors in preschool children3
The prevalence of overweight and obesity in preschool children has increased
dramatically in recent decades (1,2). Approximately one quarter of children aged 2-5
years from the USA and England are overweight or obese (2,3). Obesity is socially
patterned, with children from low socio-economic groups (4,5) or some ethnic minority
groups (2) at the greatest risk. Obese children are at greater risk of health and
psychosocial problems in childhood and adulthood (6,7) as well as adult obesity (8).
Despite the increasing prevalence of overweight in preschool children, recent reviews
have focused on the larger body of research on risk factors in school-age children and
adolescents (6,9,10). Most research has examined bivariate relationships between
childhood overweight and individual or family risk factors, such as parental overweight
(11,12), childhood television use (13,14), and diet (15,16); however, these risk factors
often do not occur in isolation. This has led researchers to develop ecological models that
conceptualise child weight gain within the context of the child and its family, community
and social factors, and social policies and national legislation (Figure 1) (6,9,10).
We used an ecological framework to structure a review of child characteristics, family
characteristics, community-level factors, and policies that influence overweight in
children aged six months to five years. We focused on factors that are amenable to policy
(legislation, regulation, or fiscal) or that have been targeted by governments or national
organisations through public health recommendations; however, risk factors which are
not amenable to policy, such as genetic factors or individuals’ nutrient intake were not
Hawkins A review of risk factors in preschool children4
reviewed. We focused on risk factors from resource-rich countries, as policies to address
overweight in resource-poor countries are likely to be different.
Search strategy and selection criteria
We identified studies through systematic searches of Medline and Embase with the
keywords “body mass index” or “obesity” or “overweight” and “infant” or “preschool
child”. These were combined with the following MeSH terms and all subcategories in
Medline: “infant nutrition”, “child nutrition”, “exercise”, “television”, “motor activity”,
“parents”, “family”, “siblings”, “employment”, “child care”, “child day care centers”,
“education”, “transportation”, “residence characteristics”, “housing”, “crime”,
“socioeconomic factors”, “restaurant”, “environment”, “recreation”, “safety”, “health
policy”. Similar keywords were used to search Embase. Each database was also searched
for the free text terms: “physical activity”, “kindergarten”, “nursery”, “restaurant”,
“recreation”, “safety”, “food outlet”, “car”, “travel”. We included articles published in
English from 1980 to March 2006. Articles from resource-poor countries were included
only if the findings were relevant to resource-rich countries.
Our search identified 1923 articles, which were assessed for their relevance. Articles of
any methodological design or duration were included if they reported at least one
measurement of body size and any of the keyword topics in a sample of children between
ages six months to five years. Cochrane reviews, meta-analyses, and other systematic
reviews were preferentially included over individual studies. Articles are reviewed within
Hawkins A review of risk factors in preschool children5
the following domains: child characteristics, family characteristics, community-level
factors, and policy. A summary of intervention studies is also included.
The most common measure of body size at the population level is body mass index
(BMI). Since there are differing cut-offs to measure overweight and obesity across
studies, we have used the term ‘overweight’ to define the top portion of the BMI
distribution. This definition will vary between studies depending on the reference growth
standard and the cut-off used for each distribution; however, a common definition has
allowed us to collate studies from different populations in order to evaluate patterns of
overweight. Within each domain, articles are grouped according to whether the outcome
is a measurement of overweight or a continuous measurement of body size, such as BMI.
Studies were not included if they only examined weight gain and no additional
measurement of body size. It is also noted whether studies controlled for potential
confounding factors, such as socio-economic circumstances, parental size or infant
We identified 59 studies (asterisked in the references) that examined at least one policy-
relevant risk factor for overweight in preschool children. Most studies investigated child
characteristics, while fewer assessed family characteristics or community-level factors,
and none evaluated the impact of a policy on overweight (Table 1). Most studies were
cross-sectional and conducted in the USA within the last ten years. Many risk factors
lacked standard definitions, which limited our ability to collate the evidence, and few
Hawkins A review of risk factors in preschool children6
studies examined risk factors from more than one domain. Furthermore, few studies
examined the relationship between a risk factor and overweight by socio-economic
circumstances and we were often unable to determine whether sub-groups may be
particularly at risk. Ethnic differences were also primarily evaluated in studies from the
USA; therefore, we did not separately comment on these findings because the results are
not likely to be generalisable to ethnic minority groups in other countries. Policies and
data from the UK and USA are provided as examples from resource-rich countries
because of the availability and accessibility of information.
Breastfeeding confers a range of health benefits for mothers and infants (17) and the
World Health Organization (WHO) recommends exclusive breastfeeding for the first six
months and continuing breastfeeding for up to two years (18). However, breastfeeding
rates vary widely across resource-rich countries, with particular disparities for exclusive
breastfeeding (19). Data from the UK and USA suggest that approximately 70% of
mothers initiate breastfeeding, with less than 15% exclusively breastfeeding at six months
Four systematic reviews have investigated the relationship between breastfeeding and
later overweight, with three reporting an inverse relationship (16,22,23) and one finding
Hawkins A review of risk factors in preschool children7
no consistent relationship (8). No difference was found between follow-up in preschool
children, older children, or adults (16,22,23). Two reviews found that an inverse
relationship still remained after adjusting for confounding factors, such as parental
obesity, maternal smoking, or social class (22,23). There is also evidence of a dose-
response relationship between duration of breastfeeding and reduced risk of overweight
(16,23). An additional systematic review found no effect of breastfeeding on mean BMI
across the life course, after adjustment (24).
We identified eleven additional studies investigating breastfeeding and overweight in
preschool children after these reviews were published (25-35). Five studies reported an
inverse relationship (25,28,29,33,34), five found no relationship (27,30-32,35), and one
reported a direct relationship (26).
Although the WHO recommends introducing solid foods into an infant’s diet at six
months of age (18), evidence suggests that infants are often weaned earlier (36,37). Early
weaning is associated with never breastfeeding and an early discontinuation of
breastfeeding (36). A systematic review of five studies found no relationship between the
age at weaning and fatness in children below age seven years (8). An additional two
studies found no consistent relationship between weaning and overweight during infancy
(38,39), while one study reported no relationship between weaning and overweight at age
five years (32).
Hawkins A review of risk factors in preschool children8
Prolonged bottle use
Some children continue to use a bottle into early childhood. In England, approximately
60% of children aged 18 months use a bottle daily (40,41) and up to 10% of children
aged 2-5 years from the USA use one (42). The Department of Health (England) and the
American Academy of Pediatrics (AAP) recommend that bottle feeding should be
discontinued after 12 and 18 months, respectively (43,44). We identified three articles
that examined the relationship between prolonged bottle use (defined as using a bottle
later than recommended) and overweight in preschool children from the USA (45-47).
Two studies found that bottle use in children aged three years was associated with an
increased risk of overweight, in both a nationally representative sample and children from
a low-income population (45,46). An additional study among primarily white, well-
educated families found no difference in mean BMI between children aged three years
with prolonged bottle use and those without (47). Only one study adjusted for potential
confounding factors (45).
While there is extensive evidence on the protective association of breastfeeding on
overweight, little is known about the relationship between weaning or prolonged bottle
use and overweight. Evidence of a dose-response relationship between duration of
breastfeeding and overweight (16,23) supports policies to encourage both breastfeeding
initiation (18,48,49) and duration (18,49). Breastfeeding is hypothesised to protect
against overweight through metabolic programming in early life (16,22,23). Studies on
Hawkins A review of risk factors in preschool children9
weaning and prolonged bottle use have often been conducted in restricted populations,
which limit the generalisability of these findings. Most studies have also not adjusted for
potential confounding factors. Despite these limitations, early weaning has been
discouraged because it replaces breast milk (17,18) and prolonged bottle use has been
found to increase the likelihood of dental caries (50). This evidence suggests that policies
to increase breastfeeding (18,48,49), delay the introduction of solid foods (18), and limit
bottle use (43,44) should be considered based on their potential for preventing early
childhood overweight and additional health benefits.
Many countries recommend that children should consume approximately five servings of
fruits and vegetables daily (51,52). Only 12% of children aged 5 years from England are
meeting this recommendation and 14% of children are having less than one portion (53).
In the USA, the mean daily intake of fruits and vegetables for children aged 2-5 years is
3.5 servings (54), although this is higher than in past decades (55).
Children’s consumption of fruit juice, sweetened drinks, and snack foods has increased
over the past 20 years (55-57). A recent study from the USA found that children aged 2-3
years from low-income families consume an average of 2.9 sweetened drinks daily (15).
Northstone and colleagues found that 48% of 18-month-old children from England
consume sweetened fruit drinks daily and 7% consume fizzy drinks (41). Furthermore,
between 1977 and 1996 the mean number of snacks consumed per day among children
aged 2-5 years has increased from 1.7 to 2.3 (57). The AAP recommends that children
Hawkins A review of risk factors in preschool children10
below age 6 months should not consume fruit juice and juice intake should be limited to
4-6 fluid ounces (118-177 mL) for children aged 1-6 years (58). Current dietary
guidelines recommend counting only one glass of fruit juice towards dietary requirements
(51) and choosing beverages with little added sugar (52).
We identified seven studies that examined the relationship between excessive fruit juice
consumption (defined as ≥ 12 fluid ounces daily [355 mL]) and overweight in preschool
children (15,59-64). Two studies reported a direct relationship (61,64) and five reported
no relationship (15,59,60,62,63). Most of these studies included small samples and often
did not adjust for confounding factors. The largest study followed over 10,000 young
children from low-income, ethnically diverse families over one year and found no
association between fruit juice consumption and overweight, after adjustment (15).
We identified only two studies that investigated sweetened drink consumption and
overweight in preschool children (15,65). Both studies from the USA reported a direct
relationship. Welsh and colleagues found that normal weight children who drank at least
one sweetened beverage daily were not at an increased risk of becoming overweight over
one year; however, overweight children at baseline with high daily sweetened beverage
consumption were twice as likely to be overweight at follow-up, after adjustment (15).
Hawkins A review of risk factors in preschool children11
Snack food consumption
There is no standard definition of snack foods; specifically, whether sweetened drinks are
included. Studies also do not often specify whether they are investigating snack
frequency or consumption. We identified five cross-sectional studies from the USA,
Europe, and Japan that investigated snack food consumption and overweight in preschool
children (29,61,66-68). Four studies reported a direct relationship (29,66-68) and one
found an inverse relationship (61).
Two studies from the same Japanese cohort found that overweight children were more
likely to not have set snack times than normal-weight children; however, snack frequency
was not related to overweight (66,67). Two European studies of preschool children found
that snacking was associated with overweight, but the association was removed after
adjustment for confounding factors (29,68). In contrast, a study of low-income Mexican-
American children found that taking food between meals was associated with a decreased
risk of overweight (61). This finding was attributed to cultural reasons, as restricting
access to food often occurs in Latino families only after a child is perceived to have a
serious weight problem (61).
Although there have been substantial changes to children’s food and beverage patterns
over the past 20 years (55-57), there is limited research on the influence of dietary factors
on overweight. We found little evidence for a relationship between fruit juice
Hawkins A review of risk factors in preschool children12
consumption and early childhood overweight. We cannot draw conclusions between
sweetened drink or snack food consumption and overweight based on the few studies we
identified, but they appear to be promising areas of research. Studies on snack food
consumption often lack a consistent definition of “snacks” and cultural factors appear to
be important for understanding their relationship to childhood overweight. Overall, the
studies on dietary factors were conducted primarily on children from the USA, had
limited sample sizes, and often did not include representative samples. Most studies were
cross-sectional and did not adjust for confounding factors. Consumption of foods, such as
drinks or snack foods, in addition to regular meals may increase energy intake and
contribute to a positive energy imbalance (15,56,57). Policies that recommend limiting
sweetened drink consumption (50,52) and introducing juice after the age of six months
(58) could prevent the displacement of breast milk and excess energy intake that may
contribute to early childhood overweight.
Physical activity/inactivity patterns
Both the UK and USA recommend that children should engage in at least 60 minutes of
physical activity daily (52,69). Although there is popular belief that physical activity has
decreased and sedentary activities have increased in recent years, there are limited data
available currently or across time (70). For example, a national survey using parent report
found that approximately one-third of English children aged 5 years are not engaging in
at least 60 minutes of physical activity daily (71). In a study using accelerometry,
Scottish preschool children are only spending 20-25 minutes per day in moderate to
vigorous activity (72). Television viewing and media use has been used as a proxy to
Hawkins A review of risk factors in preschool children 13
investigate the amount of time children are physically inactive. British children aged 4-6
years currently watch an average of 18.6 hours of television per week (73). Among
children aged 2-3 years from the USA, 41% watch 3 or more hours of television daily
(74) and 27% of children aged 4-6 years use a computer daily (75). The AAP has recently
recommended that parents should limit children’s total media time to 1-2 hours daily,
remove television sets from children’s bedrooms, and discourage television viewing for
children less than two years (76).
We identified 17 studies that investigated physical activity and overweight in preschool
children (14,29,66,67,77-89). Physical activity was recorded either through a direct
measurement of energy expenditure (14,79,83-89), observation (77,79-81,88), or parent
report (29,66,67,78,79,82). Seven studies reported an inverse relationship between
physical activity levels and body fatness (14,29,66,85-88), eight found no relationship
(67,78,79,81-84,89), and one reported a direct relationship (80). An additional study
found a direct relationship between physical activity and BMI at age four years, but an
inverse relationship at five years (77).
We found that the majority of studies examined physical activity in children aged 3-5
years and there is limited evidence on energy expenditure during infancy. A systematic
review of six studies on pre-walking physical activity and fatness in children up to age
eight years found little evidence for a relationship (8). An additional two studies reported
mixed results (86,89).
Hawkins A review of risk factors in preschool children14
Among the cross-sectional studies in children aged 3-5 years, obese children have lower
physical activity levels than normal-weight children (66,88) and low levels of physical
activity are associated with an increased risk of overweight (29). An additional study of
Japanese children found no difference in physical activity between overweight and non-
overweight children (67). The studies investigating physical activity levels and a
continuous measurement of body size reported mixed results. Children with lower levels
of physical activity have higher levels of body fatness than children with higher levels of
activity (14,87), while other studies have found no relationship (78,79,81-84). An
additional study reported a direct association between physical activity levels and child
fatness (80). Most research was conducted with predominantly white populations and
potential confounding factors were often not examined.
We identified two longitudinal studies of physical activity and overweight during the
preschool years. Moore and colleagues found that physical activity levels at age three
years were inversely related to body fatness at five years; furthermore, heavier children
with low activity levels were found to gain more weight than lean children with low
activity levels (85). Jago and colleagues reported that physical activity levels were
positively related to BMI at age four years, but negatively associated with BMI at ages
five and six years (77).
Hawkins A review of risk factors in preschool children15
Television and media use
We identified nine studies that investigated television viewing (including other media)
and overweight in preschool children (13,14,29,65,68,77,82,90,91). Television viewing
was measured either through observation (77,91) or parent report (13,14,29,65,68,82,90).
Six studies reported a direct relationship between television viewing and body fatness
(13,14,29,65,68,90) and three reported no relationship (77,82,91).
The majority of studies on television viewing were cross-sectional. Overweight children
watch more television than normal-weight children (65,90) and the number of hours of
television viewing is associated with an increased risk of overweight (13,29,68). Children
who have a television in their room are also more likely to be overweight than children
without one (13). Three cross-sectional studies that examined television viewing and a
continuous measurement of body size reported mixed results (14,82,91). Most studies
included ethnically diverse populations, but confounding factors were often not
examined. A longitudinal study by Jago and colleagues found no relationship between
television viewing and BMI at ages four or five years, but there was a significant
relationship at age six years (77).
Despite limited trend data on physical activity or media use, evidence suggests that most
preschool children are not complying with current recommendations. We found some
evidence for an inverse relationship between physical activity levels and overweight in
Hawkins A review of risk factors in preschool children16
preschool children based on longitudinal research and cross-sectional studies. We found
evidence for a direct relationship between media use and overweight based primarily on
cross-sectional studies. Media use may influence overweight by reducing participation in
physical activity (92), influencing food preferences (93), and/or increasing food
consumption during viewing (93,94). Although reverse causation could explain these
relationships, with childhood overweight leading to lower physical activity and greater
sedentary activity, there is little research in this area. There are similar limitations in the
evidence base for physical activity and media use, including the lack of a standard
definition for exposures and few longitudinal studies. Objective measures of physical
activity and media use for large samples need to be developed. Policies that limit media
use (76) could also indirectly reduce food and drink intake and subsequent weight gain.
There is an extensive evidence base to support the relationship between parental
overweight and childhood overweight (6,8,11,12). Parental overweight is also related to
children’s fat intake (84,95), snack food consumption (68,94), and a higher preference for
high-fat foods and a lower preference for vegetables (11). Children of overweight parents
are also less active (11,80) and more likely to prefer sedentary activities (11) than
children of parents with normal weight. The family environment, such as parental
modelling of eating, can influence children’s dietary behaviours (96). Children’s dietary
intake is also associated with parental diet (97). School-age children whose parents watch
Hawkins A review of risk factors in preschool children 17
high amounts of television are also more likely to watch at least two hours of television
Prepregnancy body size
The prevalence of maternal obesity in early pregnancy or prepregnancy has increased in
recent years (100,101). In Scotland, 9.4% of women were obese (BMI ≥ 30) early in
pregnancy in 1990 while 18.9% were obese in 2002/2004 (100). In the USA, 25.9% of
women were obese before or early in pregnancy in 2003 (101). Maternal prepregnancy
obesity is related to an increased risk of adverse health outcomes for mothers and infants,
including gestational diabetes (102) and a baby born large-for-gestational age (102,103).
We identified nine studies that investigated prepregancy overweight (BMI ≥ 25) and
overweight in preschool children (12,25,27,30,31,89,103-105). Seven studies reported a
direct relationship (12,25,27,30,103-105) and two found no relationship (31,89). Two
papers reported on a small sample of children who were stratified according to maternal
prepregnancy BMI. At age two years, there were no differences in BMI between the
high- and low-risk groups (89); however, children in the high risk group had higher BMIs
at ages four and six years (12). Approximately half of the studies included ethnically
diverse populations and adjusted for confounding factors.
Hawkins A review of risk factors in preschool children 18
Smoking during pregnancy
While there has been a reduction in maternal smoking during pregnancy over the past 15
years (106,107), in 2000, approximately 12% of mothers from the USA (106) and 20% of
mothers from the UK (107) smoked during pregnancy. These figures vary widely by
socio-economic and educational factors (106-110). Babies born to mothers who smoke
are at an increased risk of low birth weight (106). The USA and UK both have targets to
reduce smoking during pregnancy (49,111).
We identified 13 studies that investigated maternal smoking during pregnancy and
overweight in preschool children (25-27,29,31,103,104,108-110,112-114). All studies
reported a direct relationship. There is also evidence of a dose-response relationship
between the number of cigarettes smoked during pregnancy and an increased risk of
overweight (108,113,114). However, there are mixed results on the timing of tobacco
exposure during pregnancy and risk of overweight (109,114). Most studies included
ethnically diverse populations and controlled for confounding factors.
Employment among women with young children has increased rapidly. Over the last ten
years, maternal employment in the UK has increased from 51 to 59% for
married/cohabiting mothers with a preschool child and from 23 to 34% for lone parents
(115). In the USA, 34% of women with children under age three were employed in 1975,
while 57% were employed in 2004 (116). Policies from the UK and USA to reduce child
Hawkins A review of risk factors in preschool children19
poverty have increased the number of parents, particularly women, in employment
(117,118). Changing patterns of family life have been suggested to be partially
responsible for the rising prevalence of overweight in young children (7,119).
We identified only two studies, from the same cohort of Japanese children, that examined
maternal employment status and overweight in preschool children (66,67). They found
that obese children were more likely to have a mother in full-time employment than
children of normal weight, in univariate analyses only.
Indicators of disadvantage
Overweight in pre-school children (4,5), older children (6,120,121) and adults (121) is
socially patterned and there is strong evidence that parental circumstances are related to
risk factors for childhood overweight. While women from lower socio-economic
circumstances or with lower educational levels are less likely to begin and continue
breastfeeding (20,21), they are more likely to introduce solid foods before four months
(36,37), bottle feed their child for longer (41,42), smoke during pregnancy (106-110), and
be overweight early in pregnancy (100). Children from families with lower socio-
economic circumstances or educational levels are less likely to eat five or more fruits and
vegetables daily (53,54) and are more likely to watch a greater amount of television or
other media (74,98). There is limited or inconsistent evidence on social patterns of
sweetened drink consumption (41), snack food consumption (29,57), and physical
activity (122,123). This evidence suggests that parental circumstances influence the
development of children’s health-related behaviours early in life.
Hawkins A review of risk factors in preschool children20
Parental, particularly maternal factors, influence the development of overweight in
preschool children. We found strong support for the relationship between childhood
overweight and maternal overweight prepregnancy or smoking during pregnancy. Pre-
programming has been proposed as a potential mechanism for the association between
childhood overweight and both maternal overweight (27,30,103) or smoking during
pregnancy (25,103,108,109,114). This evidence suggests that policies should target
women before child-bearing age and continue to encourage smoking cessation during
pregnancy (49,111). Future studies should consider the role of both the pre- and post-
natal environment. Despite the speculation that an increase in maternal employment is
related to the rising rates of childhood overweight, there is limited evidence to support or
refute this claim. Additional evidence is needed to address whether changes in policies to
encourage parental employment have also influenced infant feeding, food consumption,
and physical activity/inactivity patterns. Children from families with lower socio-
economic circumstances or educational levels are at a greater risk of overweight due to
the social patterning of risk factors for obesity. This evidence can help inform the
development of interventions and policies to address health inequalities.
Hawkins A review of risk factors in preschool children21
The rapid rise in obesity has been attributed primarily to changes in environmental
factors rather than genetics (6,124). There are limited data to evaluate diet and physical
activity levels over time; however, changes in food consumption patterns (56,124) and
the built environment (70,124) may be contributing to a positive energy imbalance across
the population. The impact of specific environmental changes on weight gain and their
mechanisms remains unclear (124). Neighbourhood characteristics have been found to be
independently related to overweight, with children living in more disadvantaged areas at
higher risk (4,120). Although both the environment and the perception of the
environment influence physical activity levels (120,122), there are mixed findings about
the impact of the environment on access to food (125). Recent reviews have found that
most studies are cross-sectional and little is known about the long-term impact of the
environment on body size (124,125).
We identified three cross-sectional studies that investigated neighbourhood factors and
overweight in preschool children from the USA and Australia (82,126,127). Burdette and
Whitaker examined the impact of environmental factors on overweight in a sample of
over 7000 low-income children aged 3-4 years from the USA (126). They found no
relationship between overweight with neighbourhood safety, measured by police-reported
crimes, or with children’s residential proximity to playgrounds or fast food restaurants.
These colleagues have also found no relationship between mothers’ perceived level of
neighbourhood safety and overweight in a national sample of three-year-old children
Hawkins A review of risk factors in preschool children 22
(82). Timperio and colleagues examined parental perception of local neighbourhoods and
overweight in nearly 300 Australian children aged 5-6 years (127). Over 90% of parents
were concerned about stranger danger and road safety, but no perceptions of the
neighbourhood were associated with overweight. These studies included representative
samples of children and two studies adjusted for confounding factors.
Nursery school or day care factors
The nursery school, kindergarten (hereafter also referred to as a nursery school) or day
care environment can influence food intake and physical activity levels in young
children. In Britain, approximately 33% of employed parents use centre-based day care,
such as a nursery school or crèche (128). In the USA, approximately 24% of employed
mothers use centre-based day care for children aged 0-4 years (129). Although over 60%
of children from Britain and the USA are also cared for by informal arrangements, such
as family members or friends (128,129), there is little research in this area.
We identified two studies, from the same cohort of Japanese children, that examined
nursery school attendance and overweight in preschool children (66,67). Neither found a
difference in nursery school attendance (yes/no) between children who were obese or of
While general policies support healthy eating (51,52) and physical activity (52,69), there
are few guidelines for nursery schools or day care providers (130-133) and limited
research in these areas. Nursery school and day care settings often provide one or two
Hawkins A review of risk factors in preschool children23
main meals for children each day; however, there are few nutritional requirements for
meals (130-132). A survey of over 900 schools across the USA found that almost 9% of
children in kindergarten (approximately age 4-5 years) didn’t have any physical
education each week and only 16% had it daily (134). Children’s physical
activity/inactivity levels also vary by the day care centre (83,135) and attendance (74).
Dowda and colleagues reported that children from day care centres that offered frequent
field trips and employed college-educated teachers had higher activity levels than
children from those without (135). Similarly, Certain and Kahn found that two-year-old
children not in day care were more likely to watch at least two hours of television daily
than children in centre-based day care (74).
Although we did not identify any studies that examined dietary factors in nursery school
or day care and overweight, we located three studies that investigated nursery school-
related physical activity and overweight (134,136,137). Timperio and colleagues found
no relationship between walking or cycling to school and overweight in Australian
children aged 5-6 years (137). Metcalf and colleagues also found no difference in BMI
between English children who walked or were driven to nursery school (136). Datar and
Sturm examined changes in physical education between kindergarten and first grade
(between ages 4-5 to 5-6 years) in a nationally representative sample (134). They found
that an additional hour of physical education per week reduced BMI among girls who
were overweight, but did not alter BMI in boys or girls who were of normal weight.
Hawkins A review of risk factors in preschool children 24
Although the recent rise in obesity has been attributed primarily to environmental
changes, there is limited evidence on the impact of neighbourhood-level factors, nursery
school, or day care on overweight in young children. There are few data sources on
community-level factors and overweight at the population level, both currently and across
time. Despite a large portion of young children attending centre-based day care or nursery
school, there is little known about their dietary patterns and physical activity levels and
there are few policies targeting these areas. A lack of consistent definitions of exposures
adds an additional limitation to collating this evidence. Most research is cross-sectional
and longitudinal studies are needed to assess the impact of these factors over time.
Furthermore, children living in disadvantaged areas are at a greater risk of overweight
and little is known about how multiple influences, such as neighbourhood, family, and
individual risk factors may impact on weight gain. Future research that examines the role
of the environment, independent of and in addition to family and individual risk factors,
can be used to inform community-level interventions. Current and future policies and
targets on food intake and physical activity need to include nursery schools and day care
centres to support positive health-related behaviours within these environments.
Policies can influence childhood overweight and its determinants through legislation,
regulation, fiscal policy, or recommendations targeted at children, parents, services, and
communities. There is limited evidence on the direct relationship between policies and
Hawkins A review of risk factors in preschool children25
overweight and we did not identify any related to preschool children; however, more
research has been conducted on the impact of policies on the risk factors for overweight.
Although policies for preschool children are primarily directed at parents, community-
level policies (including day care centres and nursery schools) also influence children’s
dietary patterns and physical activity levels.
Despite targets to increase breastfeeding rates (48,49), breastfeeding often remains a
barrier for women who are employed (138). While many European countries provide
support for employed women who breastfeed, the UK and USA do not comply with even
the minimum International Labour Organization standards for protecting and supporting
breastfeeding among working mothers (139,140). Furthermore, there is no legislation to
protect breastfeeding in public in England and legislation varies by state in the USA. The
WHO and national governments have also developed policies aimed at parents on
introducing solid foods (18), bottle feeding (43,44), and fruit and vegetable consumption
(51,52), and the AAP has created policies on drink consumption (50,58). Evidence
suggests that an AAP television recommendation (76) may also indirectly impact on food
or drink consumption. Recent reviews of environmental influences on obesity have also
recommended regulating television advertising and marketing to children (10,141). In the
UK, legislation to limit food promotion to children is currently the subject of active
Hawkins A review of risk factors in preschool children 26
There are limited dietary guidelines in day care centres and nursery schools and little is
known about these practices. Nutrition policies currently only govern subsidised meals in
England (131) and the USA (132), but do not include other food and beverages that may
be served or sold on the premises. The Institute of Medicine (IOM) Committee on
Prevention of Obesity in Children and Youth recently recommended that nutritional
standards should be established for all food and beverages available in schools, including
day care centres and nursery schools (10). Although we did not identify any studies on
food policies and overweight or dietary intake in preschool children, government
programmes have been developed to improve dietary outcomes (143-145). National
programmes provide nutritional support for low-income pregnant women and children up
to age five years (143,144). England has also recently created the School Fruit and
Vegetable Scheme to provide a free piece of fruit or vegetable to all children aged 4-6
The UK and USA have developed physical activity guidelines (52,69) and the AAP has
also recommended limiting media use (76). Hayne and colleagues suggest that the limited
number of community-level policies may reflect the difficulty and time required to alter
the built environment; however, increasing neighbourhood safety and opportunities to
cycle and walk could improve physical activity levels (141). For example, a government
target in England to improve the quality of the built environment (146) may indirectly
impact on physical activity levels.
Hawkins A review of risk factors in preschool children27
There are few guidelines for physical activity and media use in day care centres and
nursery schools and limited research. In the USA, physical activity policies for day care
centres are created by each state and often do not provide any duration requirements for
physical activity or media (130). Similarly, there are no national standards in the UK
related to physical activity levels for children in day care (133). The IOM Committee
recently recommended that children should participate in at least 30 minutes of physical
activity daily while attending school, including day care and nursery school (10). The
only studies we identified that examine the impact of day care or nursery school policies
on physical activity or media use have been previously reported. Datar and Sturm found
that an additional hour of physical education per week reduced BMI among overweight
girls, but did not impact on body size among other children (134). Children’s physical
activity levels are also related to a day care centres’ policies and practices (83,135).
Despite policies and recommendations targeting diet or physical activity/inactivity among
preschool children, there is often limited information available on their implementation,
evaluation, or influence on dietary factors, physical activity, and overweight. This
evidence is primarily cross-sectional and little is known about the long-term impact of
these policies. Although children from lower socio-economic circumstances are at greater
risk of overweight, little is known about whether policies differentially affect these
children. Furthermore, we found strong evidence that parental factors influence
overweight and its risk factors in preschool children. Policies that target breastfeeding
(48,49), maternal smoking (49,111), and parental overweight (49), as well as dietary
Hawkins A review of risk factors in preschool children28
factors (49,51,52) and physical activity levels (52,69) may indirectly impact on early
A recent systematic review identified 22 interventions to prevent overweight in children
under age 18 years and 3 included preschool children (147). Dennison and colleagues
conducted a health promotion programme, based in nursery schools and day care centres
in the USA, which focused on reducing television viewing in children aged
approximately four years and their parents (148). After the seven session programme,
they found a decrease in the number of children from the intervention group who watched
more than two hours of television daily. Harvey-Berino and Rourke developed a home
visiting programme to improve the eating and exercise skills of Native American parents
and their children aged 21 months (149). They found that children in the intervention
group had less weight gain over the study period and decreased energy intake. Mo-suwan
and colleagues evaluated a kindergarten-based physical activity programme for children
aged 4-5 years in Thailand (150). After the 30 week intervention, the prevalence of
obesity decreased in children from both the intervention and control groups; however,
there was a larger decrease in the intervention group. We identified an addition
intervention by Fitzgibbon and colleagues, who developed a healthy eating, exercise, and
television viewing programme in a preschool setting for ethnic minority, low-income
children from the USA (151). At the one- and two-year follow-up, children in the
intervention group had smaller increases in BMI compared to children in the control
Hawkins A review of risk factors in preschool children29
group, but there were no differences in exercise frequency, television viewing, or dietary
Since parental overweight and health-related behaviours are related to children’s dietary
intake and physical activity/inactivity (11,68,80,84,94,95,98,99), parental involvement is
likely to be an important component of interventions for preschool children. Interventions
that target parents and their health-related behaviours, such as smoking or overweight in
pregnant women, could also have important implications for preventing overweight;
however, we did not identify any interventions that have assessed childhood overweight
as an outcome. Recent reviews have suggested that future research should include the
views of stakeholders, such as parents or communities, in the development and
implementation of interventions, assess the impact of changes to the environment, and
whether these changes are sustained after the intervention has concluded (10,147).
This review has identified policy-relevant risk factors for overweight in preschool
children. We found strong evidence for an association between early childhood
overweight and prepregnancy body size, maternal smoking during pregnancy, and
children’s television/media use. There was also strong evidence for an inverse
relationship between breastfeeding and overweight and moderate evidence for children’s
physical activity. There was limited research within the areas of weaning, prolonged
bottle use, drink consumption, snack food consumption, maternal employment, and
Hawkins A review of risk factors in preschool children30
community-level factors. Furthermore, we did not identify any policies that have been
evaluated for their impact on overweight in preschool children.
While this was not a formal systematic review, it provided a systematic approach to
collating a diverse evidence base on risk factors for early childhood overweight. As with
all reviews, it was dependent on the availability and quality of the studies in the field.
We did not formally assess the quality of these studies, but considered issues of quality
while interpreting the evidence. One such issue is the inter-relationship of some risk
factors for obesity - for example, women who are overweight (28,30) or smoke
(108,109,113) breastfeed for a shorter duration and women from lower socio-economic
circumstances are also more likely to be overweight (100) and smoke (106,107). Many
studies did not control for potential confounding factors. Furthermore, associations may
not indicate causation, particularly in cross-sectional studies which was the dominant
study design in this review. Our review considered risk factors as they applied to
populations in resource-rich countries. However, the prevalence of overweight is also
increasing in resource-poor countries (152) and we found little information on risk factors
deriving from such settings.
We found that risk factors for overweight in preschool children and gaps in the evidence
base are similar to those identified by reviews in older children (6,9,10). Although our
findings have highlighted the role of parents in early childhood overweight, there were
limited interventions targeting parents and young children. Few studies considered multi-
level factors that influence overweight or based their study of risk factors on a theoretical
Hawkins A review of risk factors in preschool children31
model. Although community-level factors and policies are also likely to influence
children’s food consumption and physical activity patterns, there was limited research in
these areas. Despite the evidence that socio-economic circumstances may differentially
affect childhood overweight and its risk factors, few studies examined health inequalities.
There was also a lack of longitudinal studies and consideration of confounding factors.
Future research should address these gaps in the evidence base.
An accumulating body of evidence highlights the importance of obesity prevention in
early life. Not only are overweight children at an increased risk of adult obesity (8), but a
recent systematic review has demonstrated that early size and growth during infancy is
related to an increased risk of obesity during childhood, adolescence, and adulthood
(153). Health-related behaviours also develop early in life and often persist across the life
course. For example, television viewing during the preschool years is a risk factor for
overweight during early childhood (13,14,29,65,68,90) as well as adulthood (154). We
also found that maternal factors during pregnancy and infant feeding decisions play a
significant role in the development of overweight. Our review suggests that the
prevention of early overweight should focus on parents, particularly mothers, and begin
before or during infancy. Governments and national organisations need to develop and
evaluate policies across domains, such as nursery school or day care and the community,
to support a healthy lifestyle in parents and their young children.
Hawkins A review of risk factors in preschool children32
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