Associations between sleeping habits and food consumption patterns among 10-11-year-old children in Finland

Abstract

The increasing prevalence of overweight and obesity among children is of special concern. Inverse associations between sleep length and overweight have been found in children. Short sleeping hours result in hormonal changes, which increase perceived hunger and appetite. This could affect food intake, and consequently lead to overweight. The aim is to find out whether there is an association between adequate sleep and food consumption among 10-11-year-old school children in Finland. One thousand two hundred and sixty-five children (response rate 79 %), aged 9-11, from thirty-one schools filled in a questionnaire about their health behaviour. Inadequate sleep was measured as short sleeping hours during school nights and weekend nights, difficulties in waking up in the morning and tiredness during the day. Food consumption patterns were measured by two consumption indices, energy-rich foods and nutrient-dense foods, based on a short FFQ (sixteen items). Inadequate sleep is associated with food consumption patterns. Boys with shorter sleep duration during school nights, and who were felt tired during the day, were more likely to consume energy-rich foods. Girls with shorter sleep duration during school nights consumed more likely energy-rich foods and less likely nutrient-dense foods. Adjusting for physical activity and screen time weakened the explored associations. The associations with energy-rich foods were stronger for boys than for girls. Sleeping habits are associated with food consumption patterns. Shorter sleep duration during school nights in school children is associated with higher consumption of energy-rich foods.

Full text

Associations between sleeping habits and food consumption patterns among
10–11-year-old children in Finland
Lisa Westerlund
1
, Carola Ray
1,2
and Eva Roos
1,2
*
1
Folkha
¨lsan Research Center, Paasikivenkatu 4, 00250 Helsinki, Finland
2
Department of Public Health, University of Helsinki, 00014 Helsinki, Finland
(Received 2 October 2008 – Revised 13 May 2009 – Accepted 21 May 2009 – First published online 7 August 2009)
The increasing prevalence of overweight and obesity among children is of special concern. Inverse associations between sleep length and
overweight have been found in children. Short sleeping hours result in hormonal changes, which increase perceived hunger and appetite.
This could affect food intake, and consequently lead to overweight. The aim is to find out whether there is an association between adequate
sleep and food consumption among 10–11-year-old school children in Finland. One thousand two hundred and sixty-five children (response
rate 79 %), aged 9–11, from thirty-one schools filled in a questionnaire about their health behaviour. Inadequate sleep was measured as short
sleeping hours during school nights and weekend nights, difficulties in waking up in the morning and tiredness during the day. Food con-
sumption patterns were measured by two consumption indices, energy-rich foods and nutrient-dense foods, based on a short FFQ (sixteen
items). Inadequate sleep is associated with food consumption patterns. Boys with shorter sleep duration during school nights, and who
were felt tired during the day, were more likely to consume energy-rich foods. Girls with shorter sleep duration during school nights con-
sumed more likely energy-rich foods and less likely nutrient-dense foods. Adjusting for physical activity and screen time weakened the
explored associations. The associations with energy-rich foods were stronger for boys than for girls. Sleeping habits are associated with
food consumption patterns. Shorter sleep duration during school nights in school children is associated with higher consumption of
energy-rich foods.
Sleep: Food consumption: Children
Overweight and obesity have increased globally during the
last decade and have now reached epidemic proportions.
The increasing prevalence of overweight and obesity among
children is of special concern, since it predicts obesity in
adult age
(1)
. Solutions as to how to stop this trend have been
sought in a number of fields, and lately attention has been
paid to sleeping habits and length of sleep. Inverse associ-
ations between sleep length and overweight have been found
in several studies and reviews, both in adults and children
(2 – 9)
.
Few studies exploring the mechanisms behind this association
have been conducted, and we need more knowledge on how
this association can be explained.
According to Patel & Hu
(5)
, a number of causal pathways
linking short sleep duration with obesity have been suggested
based on experimental studies of sleep deprivation. Sleep
deprivation might increase caloric intake either by increased
hunger or increased opportunities to eat. Short sleeping
hours result in several hormonal changes
(10 – 12)
. A decrease
in nocturnal levels of the anabolic, lipolysis-maintaining
growth hormone has been observed in the absence of
sleep
(13)
. Decrease in growth hormone could theoretically
lead to overweight due to decreased nocturnal lipolysis.
Sleep restriction also decreases circulating levels of the appe-
tite-suppressing hormone leptin, and increases levels of the
appetite-stimulating hormone ghrelin
(12,14)
. Experiments have
shown that both appetite and hunger scores are elevated by
sleep deprivation and the increases were particularly noted
for high fat and high carbohydrate foods
(15)
. This increase in
appetite could theoretically lead to changes in food intake,
especially increased intake in high fat and high carbohydrate
foods, and consequently lead to overweight due to increased
energy intake.
Overweight is a direct effect of energy intake exceeding
energy expenditure. Since food choice and consumption play
a central role in energy intake, it is of interest to study
which mechanisms affect these behavioural patterns. Food
choice might be influenced by sleeping habits, as well as by
other lifestyle-related factors
(16,17)
. Sex is also a factor that
affects food choice and should be taken into account
(18)
.
Girls tend to consume fruit and vegetables more frequently
than boys. Boys, on the other hand, drink milk more often,
but also consume fast food and unhealthy snacks more often
than girls
(16)
.
Since sleep requirement varies among individuals, sleep
length is not the only way to measure adequate sleep. Previous
studies have also included other measures reflecting sleep
status, such as difficulties waking up in the morning and tired-
ness during the day
(19,20)
. Previous research has shown that
*Corresponding author: Eva Roos, fax þ358 9 3155102, email eva.roos@folkhalsan.fi
British Journal of Nutrition (2009), 102, 1531–1537 doi:10.1017/S0007114509990730
qThe Authors 2009
British Journal of Nutrition

sleep duration during school nights is shorter than during
weekend nights and sleep duration during school nights has
a stronger association with weight than sleep duration during
weekend nights
(9)
. Sleep duration during school nights and
weekend nights may therefore have different relationships
also with food intake.
If sleep length influences food choice and meal pattern, this
could serve as one plausible mechanism behind the existing
association between short sleeping hours and overweight.
The aim of the present study is to find out whether there is
an association between adequate sleep and food choice
among 10– 11-year-old school children in Finland.
The research questions are:
1. Is there an association between sleep length during week,
during school nights and weekend nights, difficulty
waking up in the morning or tiredness during the day
and food consumption patterns in school aged children?
2. Are these associations different for boys and girls?
The hypothesis is that inadequate sleep associates with
more frequent consumption of foods with high-energy density.
Material and methods
The present study was conducted according to the guidelines
laid down in the Declaration of Helsinki and all procedures
involving human subjects were approved by the ethical
committee at the Department of Public Health, University
of Helsinki. Written informed consent was obtained from
all subjects.
The study was a part of a school health promotion research
project ‘Health workshop’ conducted by Folkha
¨lsan Research
Center, focusing on the health behaviour of school children in
Swedish speaking schools in southern Finland. Baseline data
used in the present study was collected in during years 2006.
Participants
In autumn 2006, 1265 children (616 girls and 649 boys), aged
9– 11, from thirty-one schools in southern Finland, filled in a
questionnaire about their health behaviour in a supervised
classroom situation. The response rate was 79 %.
Measures
Part of the questionnaire focused on sleeping habits, including
bedtime, wake-up time, difficulties getting up in the morning
and feelings of tiredness during the day. Bedtime and
wake-up time were asked separately for school nights
and weekend nights. It also contained a short FFQ including
sixteen groups of food items and questions on physical activity
and screen time.
Answering alternatives for bedtime and wake-up time were
listed with half hour intervals. Bedtimes were ranging from
20.00 to 24.00 hours or later on school nights, and from
20.30 to 24.00 hours or later on weekend nights. Wake-up
times ranged from 06.00 to 10.00 hours or later on school
nights and 06.30 to 10.00 hours or later on weekend nights.
Sleeping time was calculated on the basis of reported bedtime
and wake-up time on school nights and weekend nights separ-
ately. Also an average daily sleeping time for a 7-d period was
calculated from sleeping time during school nights and week-
end nights according to the formula: (5 £sleep length on
school days þ2£sleep length on weekend nights)/7.
Answering alternatives for how often the children reported
difficulty waking up in the morning and tiredness during day
were often (5– 7 times/week), sometimes (2 –4 times/week)
and seldom (0– 1 times/week).
The sixteen groups of food items included in the FFQ were:
fruit or berries; fresh vegetables; cooked vegetables; milk;
juice; coca cola or other soft drinks; juice drinks; hamburgers,
hot dogs or meat pastry; pizza; crisps or popcorn; cookies; ice
cream; sweets or chocolate; yoghurt or pudding; sweetened
breakfast cereal or sweetened muesli; rye bread. Each group
of food items was scored according to how often food items
from the group were consumed per week: never ¼0 p, less
than once a week ¼0·5 p, once a week ¼1 p, 2– 4 times/
week ¼3 p, 5 –6 times/week ¼5·5 p, once a day ¼7 p and
several times a day ¼14 p.
We also include in the analyses possible confounders,
physical activity and screen time. Physical activity was
asked as how many minutes he/she is active during normal
school nights (five answer categories) and how many hours
per week he/she is active during leisure time (six answer
categories). Screen time was asked with two questions one
focusing on how many hours daily watch TV, video or
dvd and the other focusing on how many hours daily use
computer or play Playstation Xbox or GameCube. The
answer categories were seven, from not at all to 5 h or
more per day.
Data analysis
All analyses were performed using the statistical package,
SPSS version 17.0 (SPSS, Inc., Chicago, IL, USA).
A factor analysis, a principal component analysis, of food
frequency intake data was conducted (Appendix 1) to find
food consumption patterns among the children. Two dimen-
sions were extracted from the rotated component matrix in
the factor analysis. Both dimensions had eigenvalues exceed-
ing 1. Based on these extracted dimensions, two food
consumption pattern indices were constructed. A criterion
for inclusion in the constructed indices was that the single
group of food items had a value of 0·5 or more in the rotated
component matrix. One index was labelled energy-rich foods,
and included the following groups of food items: pizza; ham-
burgers, hot dogs or meat pastry; crisps or popcorn; cookies;
ice cream; sweets or chocolate; coca cola or other soft
drinks. The other index was labelled nutrient-dense foods,
and contained the following groups of food items: fruits
and berries; fresh vegetables; cooked vegetables; rye bread.
The weekly consumption scores given for each group of
food items were added up to form the new scores for the
two indices.
Differences in sleep variables and food consumption pat-
terns between sexes were analysed for continuous variables
with Mann– Whitney’s Utest and for categorical variables
with
x
2
test. The mixed models were used to examine the pat-
terning of the continuous food consumption indices. These
food consumption indices were used as dependent variables,
while the sleep parameters, sleep length, difficulty waking
up in the morning and tiredness during the day were used as
L. Westerlund et al.1532
British Journal of Nutrition

separate independent variables. Grade level was controlled for
in all models, sex was controlled in all models with total data.
Physical activity and screen time were controlled for in
models adjusting for possible confounders. Interactions
between sex and the independent variables were computed
for each dependent– independent variable analysis. The
b
-coefficient represents the difference in the mean frequency
of consumption between the category of interest and the refer-
ence, which in the tables received the value 0. For sleep
length, the
b
-coefficient represents the addition for the mean
frequency of consumption for each hour slept. Because the
sample was collected in schools there is a possibility of
school-clustering effect as the children are nested within
schools. To account for the nested nature of the data, multile-
vel analyses were carried out for all analyses presented in
Tables 2 and 3.
Results
General characteristics of the study population are presented
in Table 1. The participants slept 9·8 h per night on average.
The sleep length was longer during weekend nights than
during school nights. Girls’ sleep length was longer than
boys’ sleep length on weekend nights. Experiencing difficulty
waking up in the morning often (5 – 7 times/week) was
reported by 25 %, whereas only 7 % reported that they often
felt tired during the day. Difficulty getting up in the morning
was more common among girls than boys and seldom or never
being tired during the day was reported more often by boys.
The score for energy-rich foods was on average 9·25, indicat-
ing a intake frequency of about 9 times/week, whereas the
score nutrition-dense foods was 18·6, about 19 times/week.
Boys had higher scores than girls for energy-rich foods,
whereas girls had higher scores for nutrient-dense foods
than boys.
Sleep length during school nights and for 7-d average was
associated with consumption of energy-rich foods, no associ-
ation with energy-rich foods was found for sleep length
during weekend nights (Table 2). When examining the associ-
ation between sleep length and consumption of energy-rich
foods, we found a significant sex interaction for school
nights (P¼0·04) and for 7-d average (P¼0·03). Sleep length
was negatively associated with energy-rich foods and this
association was stronger for boys than for girls. Boys and
girls getting a shorter night’s sleep during school nights
were more likely to consume energy-rich foods than ones
getting a longer night’s sleep.
A significant sex interaction between sleep length during
school nights (P¼0·001) and 7-d average (P¼0·006)
and nutrient-dense foods was also found. In the sex-stratified
analysis, sleep length during school days and 7-d average
was positively associated with nutrient-dense foods among
girls but not boys. Girls getting a longer night’s sleep were
more likely to consume food items included in the nutrient-
dense foods index compared with girls sleeping shorter
hours (Table 2). No association was found for sleep length
during weekend nights and nutrient-dense foods.
No sex interactions between difficulty waking up in the
morning and food consumption were found. The more often
the children reported difficulty waking up in the morning,
the more frequently they consumed energy-rich foods, and
less frequently nutrient-dense foods (Table 2).
A significant sex interaction (P¼0·001) was found between
tiredness during the day and energy-rich foods. Feeling tired
during the day was associated with energy-rich foods. This
association was stronger for boys than girls, although showing
the same thing. Children, who more often felt tired during the
day, were more likely to consume energy-rich foods, com-
pared with their less tired counterparts. Feeling tired during
the day was not associated with nutrient-dense foods, nor
were any interactions found (Table 2).
Table 1. Description of sleep-related and diet-related factors among girls and boys
(Mean values and standard deviations or distribution and number of observations)
Total Girls Boys
Mean SD Mean SD Mean SD Difference between sexes
Sleep length (h)
School days 9·65 0·79 9·68 0·73 9·62 0·84 NS
Weekend nights 10·24 1·03 10·42 0·95 10·06 1·08 ***
7-d Average 9·82 0·73 9·89 0·67 9·74 0·77 ***
Do you have difficulty in waking up in the morning? % n%n%n***
Seldom or never (0–1 times/week) 32 26 37
Sometimes (2–4 times/week 44 46 42
Often (5–7 times/week) 25 28 21
100 1232 100 606 100 626
Do you feel tired during the day? % n%n%n*
Seldom or never (0–1 times/week) 55 52 58
Sometimes (2–4 times/week 38 42 35
Often (5–7 times/week) 7 6 8
100 1238 100 609 100 629
Consumption (times/week)
Energy-rich foods 9·25 9·28 7·88 6·09 10·58 11·41 ***
Nutrient-dense foods 18·66 11·53 19·42 11·44 17·94 11·58 *
Mean values or distributions were significantly different between sexes: * P#0·05, *** P#0·001.
Sleeping habits and food choice among children 1533
British Journal of Nutrition

We further adjusted the models for physical activity and
screen time. The associations between sleeping habits and
food consumption patterns somewhat weakened for boys,
but remained statistically significant for most associations
(Table 3). For girls, the only associations that remained
statistically significant was the association between sleep
duration during school nights with energy-rich foods and
sleep length during school nights and 7-d average with nutri-
ent-dense foods.
Discussion
The present study showed that sleeping less during school
nights is associated with food consumption patterns, more fre-
quent consumption of energy-rich foods, such as fast foods
and sweets, and lower consumption of nutrient-dense foods,
such as fruits and vegetables. Sleeping less during school
nights seems to have more negative implications for boys’
food consumption patterns than for girls’ food consumption
patterns. Boys getting an inadequate sleep were more likely
to consume energy-rich foods and less likely to consume nutri-
ent-dense foods, than did girls with similar sleeping habits. On
the other hand, girls seem to benefit more from sleeping
longer. They were more likely to consume nutrient-dense
foods the longer the sleep hours, whereas no such association
was found for boys. Adjusting for physical activity and screen
time weakened the association between sleeping habits and
food consumption patterns.
Participation in the present study was voluntary, and a writ-
ten consent both from the parents and the child was needed.
This might have selected the children participating in the
study towards more health conscious individuals, whereas
the ones with a less healthy lifestyle might have chosen not
to participate. A less selective data would probably have
shown stronger associations than found in the present study.
We have used the same questions of sleep habits as in large
cross-national studies, for example the cross-national research
study Health Behaviour in School-aged Children, which is
conducted in collaboration with the WHO Regional Office
for Europe
(21)
and the Pediatric Sleep Health Program
(19)
con-
ducted by Lifespan Sleep Disorders Center. The questions
used in the questionnaire have not been validated. Because
bedtime and wake-up time answering alternatives were with
half hour intervals, sleep length could theoretically vary by
as much as 59 min within the same sleep length value. This
can affect the validity of the answers. In practice, the vari-
ation within the same sleep length value is more likely at
most 30 min.
The young age of the children participating in the study is
another aspect that calls for attention. Are children aged
9– 11 old enough to correctly assess their usual bedtime,
wake-up time and food consumption rates in average, or do
the answers mostly reflect the habits of the past few weeks?
To ask the parents, as a more reliable source of information,
to fill in the questionnaire on behalf of their children
would have been an option. On the other hand, parents do
Table 2. Associations between sleep parameters and consumption frequency of energy-rich foods and nutrient-dense foods*
(
b
-Coefficient values of ANOVA and 95 % CI)
Total† Girls‡ Boys‡
P
b
-
Coefficient 95 % CI P
b
-
Coefficient 95 % CI P
b
-
Coefficient 95 % CI
Energy-rich foods
Sleep length, school nights ,0·001 22·39 23·09, 21·68 ,0·001 21·45 22·14, 20·75 ,0·001 23·07 24·22, 21·91
Sleep length, weekend nights ,0·001 20·70 21·25, 20·16 0·18 20·36 20·89, 0·17 0·03 20·98 21·87, 20·08
Sleep length, 7-d average ,0·001 22·42 23·19, 21·66 ,0·001 21·42 22·16, 20·67 ,0·001 23·20 24·47, 21·93
Difficulty wakening up 0·008 0·21 0·04
Seldom (0 – 1 times/week) 0 0 0
Sometimes
(2– 4 times/week)
0·76 20·54, 2·06 0·59 20·66, 1·84 0·78 21·43, 2·98
Often (5– 7 times/week) 2·34 0·84, 3·83 1·23 20·14, 2·60 3·40 0·75, 6·06
Tiredness during the day ,0·001 0·04 ,0·001
Seldom (0 – 1 times/week) 0 0 0
Sometimes
(2– 4 times/week)
1·21 0·06, 2·37 1·32 0·28, 2·36 1·06 20·99, 3·12
Often (5– 7 times/week) 5·89 3·66, 8·12 1·00 21·20, 3·21 9·57 5·92, 13·23
Nutrient-dense foods
Sleep length, school nights 0·18 0·58 20·26, 1·43 ,0·001 2·37 1·09, 3·66 0·23 20·70 21·83, 0·43
Sleep length, weekend nights 0·46 0·24 20·40, 0·88 0·57 0·28 20·69, 1·24 0·63 0·21 20·65, 1·08
Sleep length, 7-d average 0·17 0·65 20·27, 1·57 0·002 2·14 0·76, 3·53 0·46 20·47 21·71, 0·77
Difficulty wakening up 0·03 0·66 0·009
Seldom (0 – 1 times/week) 0 0 0
Sometimes
(2– 4 times/week)
21·76 23·30, 20·23 20·18 22·43, 2·07 23·08 25·18, 20·98
Often (5– 7 times/week) 22·15 23·92, 20·38 21·06 23·56, 1·44 22·96 25·49, 20·42
Tiredness during the day 0·23 0·38 0·59
Seldom (0 – 1 times/week) 0 0 0
Sometimes (2– 4
times/week)
21·13 22·50, 0·24 21·24 23·14, 0·66 21·02 23·02, 0·98
Often (5– 7 times/week) 21·20 23·86, 1·46 21·64 25·60, 2·32 20·86 24·47, 2·76
* Multilevel analyses (mixed models) were carried out to taking into account the possibility of school-clustering effect.
† Sex and grade levels are controlled for in the model.
‡ Grade level is controlled for in the sex-stratified model.
L. Westerlund et al.1534
British Journal of Nutrition

not necessarily know for example what their children eat
during the day. A review article on child self-report v.
parent– proxy report makes a case for the utility of child
self-report
(22)
. Research demonstrates good reliability of
health reports by children 8– 11 years old, especially if the
questionnaires were developed specifically for this age group.
To the present knowledge, only few studies have exam-
ined the association between adequate sleep and food
habits or diet. One study on German children and adoles-
cents showed no association between sleep duration and a
nutrition quality score, which indicated the consumption of
healthy and unhealthy foods
(8)
. Another study on Japanese
school children showed that among boys sleepiness during
daytime was associated with skipping breakfast and evening
snack, whereas among girls sleepiness during daytime was
associated with daily snacking
(20)
. One study on adolescents
from Taiwan showed that adequate sleep was associated
with adopting a healthy diet, including eating breakfast
daily, eating three meals a day, drinking at least 1·5 litres
water and choosing foods with little oil
(17)
. These studies
have not carried out separate analyses for sleep duration
during school nights and weekend nights. The results from
previous studies are mainly in line with the present results,
showing that inadequate sleep is associated with unhealthy
food habits.
The plausible mechanisms behind the associations between
sleeping habits and food consumption patterns are several, and
it is possible that the mechanisms behind the associations
between sleep inadequacy and energy-rich foods differ from
the ones behind sleep adequacy and nutrient-dense foods.
Hormonal changes due to short sleeping hours have been
shown to increase perceived hunger and appetite
(15)
, and
could therefore function as a plausible mechanism behind
the observed association between sleep inadequacy and
energy-rich foods. An irregular life style, including late bed
times and irregular meal pattern, could also explain this
association. Previous studies has shown that adequate sleep
is associated with several other health-related behaviours
and it has been suggested that inadequate sleep may be a
screening indicator for unhealthy lifestyle
(17)
.
Different mechanisms for the association can perhaps
explain the sex differences found in the present study.
The mechanisms behind the associations between longer
sleep and nutrient-dense foods among girls might be explained
by upbringing and personal values. More research is needed
on why this association was not found among boys. It is poss-
ible that diligent girls follow recommendations regarding a
generally accepted lifestyle, both when it comes to sleep and
nutrition. The association between sleep duration and
energy-rich foods was stronger among boys. Also previous
studies have found stronger association between sleep and
BMI among male adolescents than among female adolescents
and a suggested explanation for the sex differences is sex
differences in the physiology, such as growth rates and
hormone secretion during puberty
(23)
.
We found a stronger association with food consumption
patterns for sleep duration of school nights compared with
weekend nights. Also studies looking at the association
between sleep duration and overweight have found stronger
associations for sleep duration during school nights than for
sleep duration during weekend nights
(9)
. School nights are
for most school children shorter than weekend nights, because
Table 3. Associations between sleep parameters and consumption frequency of energy-rich foods and nutrient-dense foods*
(
b
-Coefficients of ANOVA, adjusted for physical activity and screen time, and 95 % CI)
Total† Girls‡ Boys‡
P
b
-
Coefficient 95 % CI P
b
-
Coefficient 95 % CI P
b
-
Coefficient 95 % CI
Energy-rich foods
Sleep length, school nights 0·001 21·77 22·48, 21·05 0·04 20·74 21·44, 20·03 0·001 22·49 23·68, 21·31
Sleep length, weekend nights 0·11 20·43 20·97, 0·10 1·00 0·00 20·51, 0·51 0·10 20·74 21·63, 0·15
Sleep length, 7-d average 0·001 21·75 22·54, 20·97 0·10 20·64 21·39, 0·12 0·001 22·57 23·88, 21·27
Difficulty wakening up 0·12 0·38 0·19
Seldom (0– 1 times/week) 0 0 0
Sometimes (2–4 times/week) 0·53 20·75, 1·81 0·79 20·39, 1·98 0·19 22·02, 2·40
Often (5– 7 times/week) 1·54 0·05, 3·03 0·76 20·56, 2·08 2·32 20·35, 5·00
Tiredness during the day 0·001 0·29 0·001
Seldom (0– 1 times/week) 0 0 0
Sometimes 2– 4 times/week 0·79 20·36, 1·94 0·80 20·21, 1·81 0·73 21·35, 2·80
Often 5– 7 times/week 5·13 2·92, 7·34 0·13 21·99, 2·26 8·85 5·18, 12·53
Nutrient-dense foods
Sleep length, school nights 0·76 0·13 20·72, 0·98 0·005 1·91 0·59, 3·24 0·05 21·12 22·23, 20·01
Sleep length, weekend nights 0·98 0·01 20·62, 0·64 0·98 0·02 20·94, 0·98 0·98 20·01 20·85, 0·83
Sleep length, 7-d average 0·77 0·14 20·79, 1·06 0·03 1·61 0·19, 3·04 0·13 20·94 22·16, 0·27
Difficulty wakening up 0·14 1·00 0·03
Seldom (0– 1 times/week) 0 0 0
Sometimes 2– 4 times/week 21·51 23·00, 20·02 20·09 22·29, 2·12 22·70, 24·74, 20·67
Often 5– 7 times/week 20·89 22·62, 0·85 20·01 22·48, 2·46 21·57 24·04, 0·89
Tiredness during the day 0·84 0·98 0·79
Seldom (0– 1 times/week) 0 0 0
Sometimes 2– 4 times/week 20·06 21·41, 1·29 20·11 22·00, 1·78 20·07 22·03, 1·89
Often 5– 7 times/week 0·73 21·87, 3·32 0·21 23·70, 4·12 1·14 22·36, 4·65
* Multilevel analyses (mixed models) were carried out to taking into account the possibility of school-clustering effect.
† Sex, grade level, physical activity and screen time are controlled for in the model.
‡ Grade level, physical activity and screen time are controlled for in the sex-stratified model.
Sleeping habits and food choice among children 1535
British Journal of Nutrition

school children have to wake up early even after inadequate
sleep. During weekends children usually sleep longer nights,
because they wake up later in the morning, School nights,
however, dominate the sleep length of children and daily rou-
tines during school days are therefore of special importance
when promoting healthy lifestyle.
We also saw that adjusting for physical activity and screen
time attenuated the association between inadequate sleep and
food consumption patterns. In the analyses, physical activity
was not independently associated with food consumption
patterns, but screen time was (data not shown). It might be
that screen time influences both on sleep duration and
food consumption patterns and acts as a confounder. It is
also possible that inadequate sleep increases the amount of
screen time, which further has an impact on food consumption
patterns by increased opportunities to eat
(5)
. In that case,
screen time act as a mediator between sleep duration and
food consumption patterns.
Further studies are needed to confirm the found associ-
ations, and more comprehensive dietary assessment methods
and objective measures of sleep duration should be used,
such as actigraphy
(5)
. More knowledge is needed on whether
family rules and parents’ support or meal patterns could
explain the results. There is a possibility that that there is no
causal association between sleeping habits and eating patterns.
This is not possible to predict from these results, since this is a
cross-sectional study; therefore, there is a need for studies
with a cohort design and interventions to be able to confirm
a causal association.
In the present study, we have controlled the analyses for
sex, grade level, physical activity and screen time. The rela-
tively small sample of the study limits the possibilities to
control for a large number of factors. A larger sample would
allow for multivariate analyses, which should include different
socio-economic factors among others. Several studies have
found associations between socio-economic status and veg-
etable consumption, food choice or meal pattern
(16,18,24,25)
.
Conclusions
The results from the present study show an association
between inadequate sleep and more frequent consumption of
energy-rich foods. Among girls, an association between
longer sleeping time during school nights and consumption
of nutrient-dense foods was also found. More research is
needed to explain the association between sleeping time and
food consumption and to explain why the associations are
different depending on whether the sleep length is measured
for school nights or for weekend nights. The results from
the present study provide new knowledge of eventual mechan-
isms behind the association between inadequate sleep and
overweight and obesity, and show that sleeping habits are
associated with food consumption patterns and therefore
diet might be a mediator for the associations between sleep
and weight.
Acknowledgements
Statement reporting any conflicts of interest, funding and
contribution of each author. We have no conflicts of interest.
The present work was supported by Samfundet Folkha
¨lsan,
Juho Vainio Foundation, Pa
¨ivikki and Sakari Sohlberg Foun-
dation, Signe och Ane Gyllenberg Foundation and Victoria
Foundation. L. W. wrote and carried out the analyses of the
first version of the submitted manuscript. E. R. and C. R.
were responsible for the data collection and participated in
the planning and writing of the manuscript. E. R. carried out
further analyses and modified the text of the resubmitted ver-
sions. C. R. and L. W. participated in the planning of the
resubmitted version. All authors have read and approved the
present version of the manuscript.
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Appendix 1.
Extracted components from the rotated component matrix of the factor analysis, including all food groups used in the FFQ
Component 1 Component 2
Fruit and berries 20·057 0·682*
Fresh vegetables 20·084 0·782*
Cooked vegetables 20·001 0·676*
Milk 0·113 0·370
Juice 0·076 0·171
Coca cola or other soft drinks 0·587* 20·107
Squash 0·167 0·062
Hamburgers, hot dogs or meat pastry 0·728* 20·073
Pizza 0·667* 20·050
Crisps or popcorn 0·754* 20·021
Cookies 0·669* 0·096
Ice cream 0·664* 0·102
Sweets or chocolate 0·705* 20·055
Yoghurt or puddings 0·242 0·253
Sweetened breakfast cereal or sweetened muesli 0·343 0·034
Rye bread 20·059 0·646*
Eigenvalue 3·766 2·426
* Food groups with a value above 0·5 are included in the index.
Sleeping habits and food choice among children 1537
British Journal of Nutrition