blood samples were obtained from 686 subjects ( 300 children and 386 adolescents ) belonging to the swedish part of the european youth heart study ( eyhs ) . eyhs is a cross - sectional school - based study of risk factors for future cardiovascular disease among children ( 910 years old ) and adolescents ( 1516 years old ) . the mean ages in the swedish sample for children and adolescents were 9.6 years and 15.6 years , respectively . height , weight , hip and waist circumferences were measured by internationally accepted standardized procedures ( 18 ) . body mass index ( bmi ) was calculated as weight / height ( kg / m ) . body fat percentage was calculated by using slaughter 's equation based on skinfold thickness measurements ( 19 ) . these measurements have been shown to correlate highly with dual - energy x - ray absorptiometry - measured body fat percentages in children of similar age groups ( 20 ) . these measurements were taken using a harpenden caliper at the biceps , triceps , subscapular , suprailiac and triceps surae sites on the left side of the body . if the first two measurements differed by more than 2 mm , a third measurement was taken and the two closest measurements were averaged . the consumption of milk and milk products was assessed by an interviewer - mediated 24-hour recall . in the nine - year olds , a qualitative food record completed the day before the interview with the help of parents served as a checklist for the data obtained during the recall . dietary data were processed by stormats ( version 4.02 , rudans lttdata , sweden ) and analysed using the swedish national food database ( version 99.1 ) . the milk products of interest were milk , soured milk ( a traditional milk product , filmjlk , in swedish ) , yoghurt and cheese , both reduced- and full - fat versions . as part of a broad - ranging questionnaire , parents of the participants were asked if their child had a chronic illness or adhered to a special diet . for the genetic analysis genomic dna was isolated from whole blood samples from the individuals with the qiaamp dna blood mini kit spin procedure . the dna fragment spanning the -13910-c / t polymorphic site was amplified using a biotinylated forward - primer ( 5-gggctggcaatacagataagata-3 ) and an unbiotinylated reverse - primer ( 5-agcagggctcaaagaacaatcta-3 ) . the applied sequencing primer was : 5-ctttgaggccaggg-3. sequencing was performed using a psq96 snp reagent kit and a psq 96ma system ( pyrosequencing ab ) psq96ma 2.0.1 software . statistical analyses were performed with the statistical package for social sciences software ( spss , version 13.0 for windows ; spss inc , chicago , il ) . quantitative effects on the selected anthropometric and food intake variables were tested in two- and three - way anova / ancova models with age group ( children or adolescents ) , sex ( girls or boys ) and lct-13910 c > t genotype ct / tt vs. cc ( lnp vs. lp ) as fixed factors . adjustments for daily energy intake were performed using the residual method when body fat percentage was dependent variable in ancova models . anthropometric characteristics , total energy intake ( kj / day ) and dietary intake ( g / day ) at baseline ( n=686 ) parents and 15-year olds gave specific written informed consent to participation in the present genetic study . the study was approved by the research ethics committees of rebro county council and huddinge university hospital . blood samples were obtained from 686 subjects ( 300 children and 386 adolescents ) belonging to the swedish part of the european youth heart study ( eyhs ) . eyhs is a cross - sectional school - based study of risk factors for future cardiovascular disease among children ( 910 years old ) and adolescents ( 1516 years old ) . the mean ages in the swedish sample for children and adolescents were 9.6 years and 15.6 years , respectively . height , weight , hip and waist circumferences were measured by internationally accepted standardized procedures ( 18 ) . body mass index ( bmi ) was calculated as weight / height ( kg / m ) . body fat percentage was calculated by using slaughter 's equation based on skinfold thickness measurements ( 19 ) . these measurements have been shown to correlate highly with dual - energy x - ray absorptiometry - measured body fat percentages in children of similar age groups ( 20 ) . these measurements were taken using a harpenden caliper at the biceps , triceps , subscapular , suprailiac and triceps surae sites on the left side of the body . if the first two measurements differed by more than 2 mm , a third measurement was taken and the two closest measurements were averaged . the consumption of milk and milk products was assessed by an interviewer - mediated 24-hour recall . in the nine - year olds , a qualitative food record completed the day before the interview with the help of parents served as a checklist for the data obtained during the recall . dietary data were processed by stormats ( version 4.02 , rudans lttdata , sweden ) and analysed using the swedish national food database ( version 99.1 ) . the milk products of interest were milk , soured milk ( a traditional milk product , filmjlk , in swedish ) , yoghurt and cheese , both reduced- and full - fat versions . as part of a broad - ranging questionnaire , parents of the participants were asked if their child had a chronic illness or adhered to a special diet . for the genetic analysis genomic dna was isolated from whole blood samples from the individuals with the qiaamp dna blood mini kit spin procedure . the dna fragment spanning the -13910-c / t polymorphic site was amplified using a biotinylated forward - primer ( 5-gggctggcaatacagataagata-3 ) and an unbiotinylated reverse - primer ( 5-agcagggctcaaagaacaatcta-3 ) . the applied sequencing primer was : 5-ctttgaggccaggg-3. sequencing was performed using a psq96 snp reagent kit and a psq 96ma system ( pyrosequencing ab ) psq96ma 2.0.1 software . statistical analyses were performed with the statistical package for social sciences software ( spss , version 13.0 for windows ; spss inc , chicago , il ) . quantitative effects on the selected anthropometric and food intake variables were tested in two- and three - way anova / ancova models with age group ( children or adolescents ) , sex ( girls or boys ) and lct-13910 c > t genotype ct / tt vs. cc ( lnp vs. lp ) as fixed factors . adjustments for daily energy intake were performed using the residual method when body fat percentage was dependent variable in ancova models . anthropometric characteristics , total energy intake ( kj / day ) and dietary intake ( g / day ) at baseline ( n=686 ) parents and 15-year olds gave specific written informed consent to participation in the present genetic study . the study was approved by the research ethics committees of rebro county council and huddinge university hospital . analysis of the lct-13910 c > t genotype showed that the ct and tt genotypes , associated with lp , were found in 261 ( 87.0% ) children and 329 ( 85.2% ) adolescent subjects . the genotype lct-13910 cc that is associated with lnp was found in 37 children ( 13.0% ) and 57 adolescents ( 14.8% ) . table 2 shows an analysis of the overall effect of the lct-13910 c > t polymorphism on the studied variables using the levels tt / ct vs. cc in a three - way ancova / anova model . taken together , milk , soured milk and yoghurt intakes , specifically intakes of reduced fat versions , were significantly lower in individuals with lnp ( p < 0.001 ) . analysed separately , milk intake ( g / d ) and specifically reduced fat milk ( g / d ) was lower ( p=0.001 and p<0.001 , respectively ) in lnp children and adolescents . body fat percentage ( adjusted and unadjusted for energy intake ) as well as daily energy intake were not related to the lct-13910 c > t genotype . table 2 presents the distribution of milk and milk product intake - related variables , which were significantly related to the genotype in table 2 , stratified for age group and sex , and according to lct-13910 c > t genotypes . effects of genotype , sex and age group , on total energy intake ( kj / day ) , dietary intake ( g / day ) and body fat ( % ) 
							 three - way anova , lct-13910 c > t ( cc vs. ct / tt ) , sex and age group as factors . three - way ancova , lct-13910 c > t ( cc vs. ct / tt ) , sex and age group as factors ; adjusted for daily energy intake ( kj / d ) . effects of genotype on milk intake related variables significant in table 2 ( stratified by age group ) 
							 lct-13910 c > t polymorphism . two - way anova : lct-13910 c > t ( cc vs. ct / tt ) and sex as factor . as shown in table 3 , after subsequent partitioning of milk and milk product intake - related variables , the lct-13910 cc genotype was associated with statistically significantly lower intake of total milk , soured milk and yoghurt ( p=0.002 for children and p=0.023 for adolescents ) . milk intake was significantly lower in lnp children ( p=0.005 ) and in lnp adolescents ( p=0.043 ) compared to lp children and adolescents . analysed by fat content , the cc genotype was associated with significantly lower intake of total reduced fat milk , soured milk and yoghurt , in both children and adolescents ( p=0.009 and p=0.019 , respectively ) . reduced fat milk intake was also significantly lower in lnp children and adolescents ( p=0.010 and p = 0.001 , respectively ) . no statistically significant interactions of the lct-13910 c > t polymorphism with age and sex for the selected variables were found in either the two - way ancova / anova or three - way ancova / anova models . in response to a question about the presence of chronic conditions in , or adherence to special diets by , their children , parents reported lactose intolerance in just six cases ( two children and four adolescents ) . none of these cases demonstrated genetically determined lnp . we conducted the current study to investigate the possible differences in dairy product intake and in body fat mass among lp and lnp children and adolescents . there was a statistically significant difference between milk and milk product consumption in lp and lnp subjects . interestingly , lp children and adolescents consumed statistically significantly more reduced fat milk than lnp subjects . concerning the key question of our study , whether lp and lnp influence the consumption of milk and milk products , which in turn could be associated with differences in body fat mass , we found no differences between lp and lnp as regards body fat mass . a recent study , performed on the national health and nutrition survey ( nhanes ) 19992004 , showed that a dietary pattern characterised by greater milk intake was associated with increased bmi among preschool children ( 23 ) . sweden has traditionally one of the highest consumption rates of milk in the world ( 24 ) and we hypothesise that the potential physiologic effects of single food components , such as milk and milk products , may differ between countries due to their particular food and farming culture , agricultural inheritance and geographical as well as climatic singularities . the higher consumption of reduced fat milk , compared to full - fat milk , in all age and genotype groups might reflect a secular trend . krachler et al . ( 25 ) reported in 2005 a switch from 3% of fat milk to 1.5% of fat milk among northern swedes that occurred between 1986 and 1999 . about 83% of the lnp individuals consumed some amount of milk . on average , they consumed 421 g ( 95% ci 399 , 502 ) milk per day . this is compatible with many studies showing that lnp subjects can tolerate a certain amount of lactose intake per day ( 6 , 2628 ) . concerning the high prevalence of lnp ( 14% ) compared to the traditional prevalence data of lnp in sweden ( 2% ) , we have found a trend towards an increasing prevalence of lnp in sweden . this increase seems to have taken place in the course of the second half of the twentieth century due to higher immigration rates to sweden after the second world war ( 29 ) . the strengths to be considered in this study are that we use the concept of mendelian randomisation ( mr ) , by subdividing genotypes in lp and lnp , to readdress the question of whether nutrigenetically defined factors , like milk and milk product intake , affect body fat mass in children and adolescents . mr studies modifiable causes of disease in genetic epidemiology . a functional genetic variant , in our study lct-13910 c > t polymorphism , acts as proxy for modifiable lifetime exposure patterns , i.e. milk consumption . the lct-13910 c > t polymorphism is known to influence the exposure pattern , milk consumption ( 2 , 5 , 6 , 3032 ) . in addition , we analysed both , full fat and reduced fat varieties as regards the key question of this work . limitations of this study include the drawbacks inherent to 24-hour dietary recall , which may not fully reflect long - term food intake behaviour ( 33 ) . yet the genetically determined condition of lp or lnp , which we studied in this work , is not subject to changes during life . the results should be interpreted bearing in mind the limitations inherent in any cross - sectional study . furthermore , results of genetic epidemiological studies obtained in one defined population should not be applied without reserve to other populations or ethnic groups . the age of onset of lnp shows a wide regional and ethnical variation ( 4 ) . in persons of european descent , the onset of genetically determined lnp is rarely seen before five years of age ( 3436 ) ; finnish children who develop lnp have done so by the age of 10 ( 4 ) . thus , it could be assumed that the majority of children and almost all adolescents with lct-13910 cc genotype had developed manifest lnp at the time of inclusion in this study . however , the correlation between lnp and self - reported  lactose intolerance has been previously suggested to be poor ( 3739 ) , which we confirm in this study : six cases parents reported  lactose intolerance in their children , in two children and four adolescents , and none of them were lnp according to genotyping data . in conclusion , lp is linked to an overall higher milk and dairy intake , but is not linked to higher measures of body fat mass in children and adolescents . this study was supported by grants from rebro lns landstings forskningskommitt and by nyckelfonden , rebro , sweden .
backgroundlactase non - persistent ( lnp ) individuals may be lactose intolerant and therefore on a more restricted diet concerning milk and milk products compared to lactase persistent ( lp ) individuals . 
 this may have an impact on body fat mass.objectivethis study examines if lp and lnp children and adolescents , defined by genotyping for the lct-13910 c > t polymorphism , differ from each other with regard to milk and milk product intake , and measures of body fat mass.designchildren ( n=298 , mean age 9.6 years ) and adolescents ( n=386 , mean age 15.6 years ) , belonging to the swedish part of the european youth heart study , were genotyped for the lct-13910 c > t polymorphism . 
 dietary intakes of reduced and full - fat dairy varieties were determined.resultslnp ( cc genotype ) subjects consumed less milk , soured milk and yoghurt compared to lp ( ct / tt genotype ) subjects ( p<0.001 ) . 
 subsequent partitioning for age group attenuated this observation ( p=0.002 for children and p=0.023 in adolescents ) . 
 six subjects were reported by parents to be  lactose intolerant , none of whom were lnp . 
 lnp children and adolescents consumed significantly less reduced fat milk and milk products than lp children and adolescents ( p=0.009 for children and p=0.001 for adolescents).conclusionswe conclude that lp is linked to an overall higher milk and dairy intake , but is not linked to higher body fat mass in children and adolescents .