Study On The Relationships Of Metabolic Syndrome With Dietary Iron And Gene Polymorphisms And Their Interactions

Objective:To study the relationships of metabolic syndrome(MetS)with dietary iron and gene single nucleotide polymorphism(SNP),as well as the possible interaction between dietary iron intake and SNP in the association within MetS risk.The specific objectives were ?to study the relationships between dietary iron and MetS in the adult population in metropolis of China;and? to study the relationships between SNP and the risk of MetS,and the possible interactions with dietary iron intake.Methods:The epidemiological methodology of case-control was applied in the current study.In the first part of the study,5323 participants aged 18 and above of four municipalities from China Nutrition and Health Survey and Shanghai Diet and Health Survey were recuited.In the second part,3,099 participants aged 18 and above from Shanghai Diet and Health Survey were recuited.The study included a 3-consecutive-day-24-hour dietary recall along with collecting condiment weighting data to obtain information of dietary intake;the intakes of dietary energy and iron were estimated according to daily food and condiment consumption using the Chinese food composition database;a general questionnaire to obtain demographic information and risk factors for MetS(age,sex,income,body activity,scheduled workout,daily total dietary intake,smoking condition,drinking condition);and a unified physical examination to obtain participants'height,weight,waist circumference,and blood pressure information.Early morning fasting blood of the participants were collected and analyzed:separated blood serum to detect glucose and lipid indicators by using HITACHI 7080 and 7600 automatic biochemical analyzer;separated white blood cell to extract DNA by using magnetic-bead-method universal genomic DNA extraction kit(type DP705-02 from TIANGEN)and to detect target gene loci by using genetic inheritance analyzer(type 3730XL from Applied Biosystems from the United States of America).MetS was identified based on the criteria in the US National Cholesterol Education ProgramAdult Treatment Panel ?(NCEP-ATP ?)for Asian populations.Statistical analysis was done by SAS(v.9.4;SAS Institute,Cary,NC,USA).The relationships between dietary iron,gene polymorphisms,and the risk of MetS were analyzed by using multivariate generalized mixed linear models based on logit link function and multi-level logistic regression models.Results:In the first part,the analysis sample included 5323 participants from four municipalities.After adjusting for age,sex,region,years of education,physical activity level,intended physical exercises,smoking status,alcohol use,daily energy intake and further adjustment for zinc and magnesium,a significant positive trend was found across quartiles of dietary total iron and the risk of MetS(p value for the trend=0.01).Compared with the lowest quartile of dietary total iron intake(<13.14 mg/day),the highest quartile(?21.41 mg/day)had an OR(95%CI)of 1.60(1.21,2.11).The trend between non-haem iron and MetS was similar with that between total iron and MetS,while the trend between haem iron and MetS was on the contrary.After adjusting for age,sex,region,years of education,physical activity level,intended physical exercises,smoking status,alcohol use and daily energy intake(Model 2),iron from vegetables and fruit was negatively associated with MetS risk(p=0.01).After further adjusting for zinc and magnesium from the same food sources(Model 3),the trends were no more statistically significant(p=0.72).In the second part,the analysis sample included 3099 participants.After adjusting for age,sex,income,physical activity level,intentional physical exercise,dietary energy intake,smoking status and alcohol use,a significant positive trend was found across quartiles of total dietary iron intake and risk of MetS(p for trend=0.022).Compared with the lowest quartile of dietary total iron intake(<12.72 mg/day),the highest quartile(?21.88 mg/day)had an OR(95%CI)of 1.59(1.15,2.20).However,after adjusting for the same confounders,there was no association between heme dietary iron intake and risk of MetS(p for trend=0.895).Although the quartiles of nonheme iron intake were not in line with the risk of MetS(p for trend=0.065),the highest quartile of nonheme iron intake(?20.10 mg/day)had a 1.44-fold higher risk of MetS compared with the lowest quartile(<11.62 mg/day).After stratifying by gender,the linear trend between the quartiles of total dietary iron intake and risk of MetS was still significant in male participants(p for trend=0.016)but not in female participants(p for trend=0.322).2766 participants who has genotyping test results were included in the analysis of the relationships between SNP and the risk of MetS,and the possible interactions with dietary iron intake.Among the selected 14 gene loci,there were 4 loci asscociated with MetS risk.Among all participants,after adjusting for age,region,years of education,physical activity level,intended physical exercises,smoking status,alcohol use and daily energy intake,dietary iron and SNP of MTNR1B rs10830963 were in line with MetS risk(p=0.003,0.049)with 0.25 and 0.50? values,repectively.There was no interaction between dietary iron and SNP of MTNR1B rs 1083096(p=0.169).Among male participants,after adjusting for age,region,years of education,physical activity level,intended physical exercises,smoking status,alcohol use and daily energy intake,dietary iron and SNP of JAZF1 rs864745 were in line with MetS risk(p<0.001,p=0.037)with 0.37 and 0.76 ? values,repectively.The interaction of dietary iron and SNP of JAZF1 rs864745 existed(p=0.029).Dietary iron and SNP of ANK1 rs516946 were in line with MetS risk(p<0.001,0.019)with 0.34 and 1.02? values,repectively.The interaction of dietary iron and SNP of ANK1 rs516946 existed(p=0.007).Among female participants,after adjusting for age,region,years of education,physical activity level,intended physical exercises,smoking status,alcohol use and daily energy intake,dietary iron and SNP of rs2794720 were in line with MetS risk(p=0.009,0.011)with 0.56?1.69?values,repectively.The interaction of dietary iron and SNP of rs2794720 existed(p=0.029).Conclusion:Dietary iron intake among majority of adult population in metropolis exceeded the recommended level.Total and nonheme dietary iron intake was positively associated with MetS and its components in the adult participant in metropolis of China,that is,the risk of metabolic syndrome was higher at a higher level than that at a lower level,especially at a level above the recommended level.But an association between heme iron intake and MetS was not observed.The risk of MetS varied with dietary iron from different food sources.Dietary iron from vegetables and fruits might be a protective factor for MetS.Moreover,gender differences in the association between dietary iron intake and the occurrence of MetS was found:higher levels of total and nonheme iron intake were associated with greater risks of MetS in men but not in women.The polymorphisms of MTNR1B rs10830963,JAZF1 rs864745,ANK1 rs516946 and rs2794720 were correlated to the risk of MetS,and there were gender differences in this relationship.Gene SNP interacted with dietary iron intake in the relationship with MetS.Individuals carrying risk alleles,regardless of the level of dietary iron intake,had a higher MetS risk than those not carring and the risk was no more associated with dietary iron intake;among individuals not carrying risk alleles,there was a significant positive linear trend between dietary iron and the risk of MetS.