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February 2007

Cardiovascular Fitness Is Negatively Associated With Homocysteine Levels in Female Adolescents

Author Affiliations

Author Affiliations: Department of Medical Physiology, School of Medicine, University of Granada (Messrs Ruiz and Ortega and Drs Sola, Gonzalez-Gross, Gutierrez, and Castillo), Unit of Hematology, University Hospital San Cecilio, Granada (Dr Sola), E. U. Ciencias de la Salud, University of Zaragoza (Dr Vicente-Rodriguez), School of Sport Sciences, Universidad Politécnica de Madrid (Dr González-Gross), and Department of Pediatrics, University of Cantabria, Santander (Dr Garcia-Fuentes), Spain; Unit for Preventive Nutrition, Department of Biosciences and Nutrition at NOVUM, Karolinska Institutet, Huddinge, Sweden (Dr Sjöström and Messrs Ruiz and Ortega); and Institut fuer Ernaehrungswissenschaft, Pathophysiologie der Ernährung, Rheinische Friedrich-Wilhelms Universität, Bonn, Germany (Dr Pietrzik).

Arch Pediatr Adolesc Med. 2007;161(2):166-171. doi:10.1001/archpedi.161.2.166

Objective  To examine the association between cardiovascular fitness and homocysteine levels in adolescents.

Design  Cross-sectional study.

Setting  Madrid, Murcia, Granada, Santander, and Zaragoza, Spain.

Participants  One hundred fifty-six Spanish adolescents (76 boys and 80 girls) aged (mean ± SD) 14.8 ± 1.4 years.

Main Exposures  Cardiovascular fitness was measured by the 20-m shuttle run test. Pubertal stage, birth weight, smoking status, and socioeconomic status were determined, and the sum of 6 skinfold thickness measurements, and serum folic acid and vitamin B12 levels were measured. Methylenetetrahydrofolate reductase (MTHFR; 677C>T genotype) polymorphism was done by DNA sequencing.

Main Outcome Measure  Fasting homocysteine levels.

Results  Mean values of homocysteine were significantly higher in the MTHFR 677CT and TT genotype subgroups compared with the CC genotype subgroup in adolescent boys, whereas in adolescent girls, mean values of homocysteine were significantly higher in the MTHFR 677CT and TT genotype subgroup compared with the CC and CT genotype subgroups. Multiple regression analyses showed that cardiovascular fitness was significantly associated with homocysteine levels in female adolescents after controlling for potential confounders including the MTHFR 677C>T genotype (β = −0.40; semipartial correlation = −0.35;  = .007). No associations were found between cardiovascular fitness and homocysteine levels in male adolescents (β = 0.12; semipartial correlation = 0.08;  = .51).

Conclusion  The results suggest that cardiovascular fitness is negatively associated with homocysteine levels in female adolescents after controlling for potential cofounders including MTHFR 677C>T genotype.

Homocysteine has been suggested to be an independent risk factor for several multisystem diseases,1 including coronary heart disease,2,3 stroke,4 dementia, and Alzheimer disease,5 as well as for risk of hip fracture6 and pregnancy complications.7 Moreover, elevated homocysteine levels have been associated with increased oxidative stress and endothelial damage,8,9 although the mechanisms are not yet clarified. In children, elevated homocysteine levels are positively associated with cardiovascular disease in their parents,10,11 grandparents,12,13 and other relatives.14

Homocysteine levels are influenced by modifiable and nonmodifiable factors. Among the nonmodifiable factors, age and sex seem to have a specific role. Levels of homocysteine are higher in adolescent boys than in adolescent girls, and this sex effect seems to be enhanced during and after puberty.15 Genetic factors also seem to affect homocysteine levels.16-19 Elevated levels of homocysteine can be caused by mutations in enzymes involved in homocysteine metabolism, which give dysfunctional enzymes, for example, the single-nucleotide polymorphism at position 677 in the methylenetetrahydrofolate reductase (MTHFR) gene for MTHFR.17 Methylenetetrahydrofolate reductase is a key enzyme in homocysteine metabolism. The common polymorphism 677C>T gives a thermolabile form of the enzyme. Subjects homozygous for this mutation (or TT genotype) have higher levels of homocysteine compared with subjects with CC or CT genotypes.18,19

Deficient serum levels of both folic acid and vitamin B12 have been associated with elevated homocysteine levels in children,18 adults,20 and elderly persons.21 Lifestyle factors such as smoking, lack of physical activity, excessive alcohol intake, and obesity have been associated with elevated levels of homocysteine in adults.20,22-24

Poor cardiovascular fitness (CVF) is another important risk factor for cardiovascular disease and is a predictor of morbidity and all-cause mortality.25,26 Kuo et al27 have recently described a significant negative association between CVF and homocysteine levels in women. Cardiovascular fitness has been negatively associated with features of metabolic syndrome in children and adolescents28,29 and with plasma lipid profile in both overweight and nonoverweight adolescents.30 However, studies examining the association between CVF and homocysteine levels in adolescents are lacking. We hypothesized that there would be a negative correlation between CVF and homocysteine levels in adolescents. For public health strategies and preventive purposes, it is of interest to understand the relative influence of modifiable factors on homocysteine levels from an early age.


The study participants were a subsample of the AVENA (Alimentación y Valoración del Estado Nutricional de los Adolescentes Españoles [Food and Assessment of the Nutritional Status of Spanish Adolescents]) study, which was designed to assess the health and nutritional status of adolescents. The AVENA study design has been reported in detail elsewhere.31-33 Data were collected from November 6, 2000, to June 28, 2002, in 5 Spanish cities: Madrid, Murcia, Granada, Santander, and Zaragoza. Data in the present article are from adolescents in whom both homocysteine levels and MTHFR genotypes were measured (n = 156; 76 boys and 80 girls).

A comprehensive verbal description of the nature and purpose of the study was given to both the adolescents and their teachers. Written consent to participate was requested from parents and adolescents. Adolescents with a personal history of cardiovascular disease, who were taking medication at the time of the study, or who were pregnant were excluded. The study protocol was performed in accord with the ethical standards established in the 1961 Declaration of Helsinki (as revised in Hong Kong in 1989 and in Edinburgh, Scotland, in 2000) and was approved by the Review Committee for Research Involving Human Subjects of the Hospital Universitario Marqués de Valdecilla, Santander.

Before any testing was performed, the parents completed a questionnaire, part of which addressed the adolescent's previous and current health status. Socioeconomic status was also assessed in the questionnaire and was defined by the educational achievement and occupation of the father. According to this information and following the recommendation of the Spanish Society for Epidemiology,34 the adolescents were classified into 5 socioeconomic categories: low, medium low, medium, medium high, and high. Smoking status at the time of the study was reported via questionnaire completed by the adolescents, and they were categorized as smoker, nonsmoker, and occasional smoker (ie, once a week).

Physical examination

Anthropometric measurements were obtained as described elsewhere.35-37 In brief, skinfold thickness was measured to the nearest 0.2 mm at the biceps, triceps, subscapular, suprailiac, thigh, and calf on the left side of the body. The sum of the 6 skinfold thicknesses was used as an indicator of body fat. These measurements correlate highly with measured body fat percentage in adolescents of similar ages as measured with dual-energy x-ray absorptiometry.38

Identification of pubertal stage was assessed according to the method of Tanner and Whitehouse.39 Self-reported breast development in adolescent girls and genital development in adolescent boys was used for pubertal stage classification.

Measurement of cvf

Cardiovascular fitness was assessed by the 20-m shuttle run test as previously described.40 In brief, participants were required to run between 2 lines 20 m apart while keeping pace. Running pace was determined by audio signals emitted from a prerecorded cassette tape. The initial speed was 8.5 km/h, which was increased by 0.5 km/h per minute (1 minute equal to 1 stage). The tape used was calibrated over 1 minute. Subjects were instructed to run in a straight line, to pivot on completing a shuttle, and to pace themselves in accord with the audio signals. The test was finished when the subject failed to reach the end lines concurrent with the audio signals on 2 consecutive occasions or when the subject stopped because of fatigue. All measurements were carried out under standardized conditions on an indoor rubber-floored gymnasium. Constant vocal encouragement was given to participants throughout the test. All participants were familiar with the test because the 20-m shuttle run test is one of the fitness tests included in the physical education curriculum in Spain. Adolescents were instructed to abstain from strenuous exercise in the 48 hours preceding the test.

Cardiovascular fitness was considered as the number of stages completed (precision of 0.5 steps) for being the most direct measurement obtained. Moreover, for the purpose of comparing the results with those of previous publications, maximal oxygen consumption (V̇O2max, milliliters per kilogram per minute) was estimated by the Leger equation40: V̇O2max = 31.025 + [(3.238S − 3.248A) + 0.1536SA], where A is age and S is final speed (S = [8 + 0.5] × number of stages completed). The reliability and validity of this test has been shown in young persons.41,42


With the subject in the supine position, blood samples were obtained by venipuncture after an overnight fast, using vacuum tubes (Vacutainer; Becton, Dickinson and Co, Franklin Lakes, NJ), and placed on ice immediately. The fasting state was verbally confirmed by the subject before blood sampling. All samples were processed within 1 hour by centrifugation, divided into aliquots, and the portions stored at −80°C until withdrawn for analysis.

Homocysteine in acidified citrated plasma43 was assayed using a fluorescence polarization immunoassay on an IMx unit (Abbott Laboratories, Abbott Park, Ill). Serum folic acid and vitamin B12 levels were measured using the fluorometric method with an IMx automatic analyzer (Abbott Laboratories).


Total blood DNA was extracted and purified from 500 μL of whole blood anticoagulated with EDTA using the Quiagen procedure described by Higuchi.44 Genotyping of the 677C>T variant in the human MTHFR gene was performed by means of polymerase chain reaction and allele-specific restriction digestion of the amplified products with the restriction enzyme HinfI (GE Healthcare, Buckinghamshire, England), as previously described by Frosst et al.17

Statistical analysis

Data are given as mean ± SD unless otherwise indicated. After serum folic acid and vitamin B12 concentrations were normalized by natural logarithm transformation, all of the residuals showed a satisfactory pattern.

The effect on homocysteine levels of sex and MTHFR 677C>T were analyzed by 1-way analysis of variance because there was a significant interaction between sex and MTHFR 677C>T. The subgroup means were compared using the Tukey test.

After bivariate correlation analysis, multiple regression analyses were used to study the relation between homocysteine levels and CVF after controlling for potential confounders. We used an extended-model approach: Model 1 examined the influence of CVF on homocysteine levels after controlling for age, pubertal stage, birth weight, smoking status, socioeconomic status, and the sum of 6 skinfold measurements. Model 2 examined the influence of CVF on homocysteine levels after controlling for the confounders included in model 1 plus serum folic acid and vitamin B12 levels. Model 3 examined the influence of CVF on homocysteine levels after controlling for the cofounders included in model 1 and model 2 plus the MTHFR 677C>T genotype. Semipartial correlation was used as a measure of the relationship between CVF and homocysteine levels after controlling for the effect that 1 or more additional variables (eg, age or birth weight) had on one of those variables. The analyses were performed using Statistical Package for Social Sciences software (version 14.0 for Windows; SPSS Inc, Chicago, Ill), and the level of significance was set at  = .05.

Data completeness and baseline characteristics

Both homocysteine levels and the MTHFR genotype were measured in 156 adolescents (76 boys and 80 girls). Of these, 23% of the adolescents refused to continue the 20-m shuttle run test because of discomfort or distress, and their results are not included in the final data sample. The observed power for the sample size was 0.40. Pubertal stage was obtained from 96% of the subjects, and skinfold thickness data from 94%. Birth weight, socioeconomic status, and smoking status were available for 93%, 87%, and 71% of the subjects, respectively.

The descriptive characteristics of the study sample are given in Table 1. Adolescent boys were significantly heavier and taller than adolescent girls, and girls had significantly higher skinfold thicknesses. Adolescent boys had significantly higher levels of homocysteine, lower levels of serum vitamin B12, and significantly higher CVF levels (Table 1).

Table 1. 
Descriptive Characteristics of the Subjects*
Descriptive Characteristics of the Subjects*

Mean values for homocysteine levels were significantly higher in the CT and TT genotype subgroups compared with the CC genotype subgroup in adolescent boys (CC, 61.6 ± 10.0 mg/L [8.3 ± 1.4 μmol/L]; CT, 81.9 ±40.0 mg/L [11.1 ± 5.4 μmol/L]; TT, 94.5 ± 40.5 mg/L [12.8 ± 5.5 μmol/L]; CT vs CC,  = .01; TT vs CC,  = .003), whereas in adolescent girls, mean values for homocysteine were significantly higher in the TT subgroup compared with the CC and CT subgroups (CC, 55.5 ± 16.8 mg/L [7.5 ± 2.3 μmol/L]; CT, 61.6 ± 12.7 mg/L [8.3 ± 1.7 μmol/L]; TT, 75.3 ± 16.6 mg/L [10.2 ± 2.2 μmol/L];  = .001). Bivariate correlations between homocysteine levels and the studied independent variables are given in Table 2.

Table 2. 
Bivariate Correlations Between Homocysteine Level* and Independent Variables
Bivariate Correlations Between Homocysteine Level* and Independent Variables
Relations between homocysteine levels and cvf controlling for different confounders and separated by gender

The results of the regression models using the homocysteine level as the outcome variable are given in Table 3. Variation in homocysteine levels was significantly explained by CVF (expressed as number of stages completed) in female adolescents after controlling for age, pubertal stage, birth weight, smoking status, socioeconomic status, and the sum of 6 skinfold thicknesses (model 1). Additional adjustments for serum folic acid and vitamin B12 levels (model 2), and MTFHR 677C>T genotype (model 3) further strengthened the association between the homocysteine level and CVF in adolescent girls. No significant association was found between the homocysteine level and CVF in adolescent boys. The results did not change when the analyses were performed with CVF expressed as V̇O2max, or speed (data not shown).

Table 3. 
Association of Cardiovascular Fitness (Expressed as Number of Stages Completed) With Homocysteine Level*
Association of Cardiovascular Fitness (Expressed as Number of Stages Completed) With Homocysteine Level*

The results of this study suggest that CVF is negatively associated with homocysteine levels in female adolescents but is not associated with homocysteine levels in male adolescents. The results also suggest that homocysteine levels are higher in adolescent boys than in adolescent girls, that serum folic acid and vitamin B12 levels are negatively associated with homocysteine levels, and that MTHFR 677C>T genotype has an important role in homocysteine levels. To our knowledge, there are no other available data on the association of homocysteine levels with CVF in adolescents.

Cardiovascular fitness is a direct marker of physiologic status and reflects the overall capacity of the cardiovascular and respiratory systems and the ability to carry out prolonged strenuous exercise.45 In theory, disturbances in the peripheral tissues and related vasculature or in the coronary arteries and the heart may decrease CVF. High CVF levels during childhood and adolescence have been associated with a healthier metabolic profile during these years.29,30 Moreover, CVF has recently been associated with arterial compliance in children aged 9 to 11 years, which supports the concept that CVF may exert a protective effect on the cardiovascular system from an early age.46 It is biologically plausible that a high CVF level provides more health protection than a low CVF level, even in healthy adolescents, as has been found in adults.25,26

Homocysteine is metabolized to homocysteine thiolactone by methionyl transfer RNA synthetase. Homocysteine thiolactone acylates lysine residues of proteins, a process called protein homocysteinylation.47 Protein homocysteinylation is a possible mechanism of homocysteine-related protein damage, which in conjunction with the increased oxidative stress and endothelial damage seen in subjects with elevated homocysteine levels may result in impaired CVF.9 However, this cannot explain why the association between the homocysteine level and CVF is found only in female adolescents. Our findings support those of a previous study that examined the relationship between homocysteine levels and CVF in adults.27 Kuo et al27 showed that high homocysteine levels were negatively associated with estimated CVF in women. However, they did not find any association in men, which is in accord with our results. These results suggest that sex hormones may have a role in mediating the CVF-homocysteine association, exerting different effects in female and male subjects; however, further studies to determine whether this is the case are needed. One longitudinal study observed 499 independent community-dwelling elderly persons for 3 years and found that those with elevated homocysteine levels were at increased risk of decline in physical function.48 However, CVF data were not provided and a comparison by sex was not performed.

None of the previous studies included the MTHFR 677C>T genotype, which affects homocysteine levels.16-19 Balasa et al19 found that the MTHFR 677C>T polymorphism was an independent determinant of homocysteine levels in 197 healthy US children aged 6 months to 16 years. Similarly, Papoutsakis et al18 reported in a sample of healthy Greek children that the TT genotype was associated with homocysteine concentrations. Homocysteine levels in our study sample were significantly higher in the MTHFR 677CT and TT genotype subgroups compared with the CC subgroup in adolescent boys, whereas in adolescent girls, mean values of homocysteine were significantly higher in the TT genotype subgroup compared with the CC and CT genotype subgroups.

In the present study, CVF was objectively measured by the 20-m shuttle run test. We did not have a direct measurement of V̇O2max, the most valid method of measuring CVF. However, from a practical point of view, field tests may be a better option than laboratory testing, especially in epidemiologic studies, because a large number of subjects can be tested at the same time, which enhances the motivation of the participants, and the tests are simple, safe, and often the only feasible choice, especially in school settings. The 20-m shuttle run test meets these criteria. Cardiovascular fitness was considered as the number of stages completed in the 20-m shuttle run test. However, CVF estimated from the Leger equation (V̇O2max, milliliters per kilogram per minute) was also provided for the purpose of making comparisons with other studies possible. When the analyses were performed using V̇O2max or speed (kilometers per hour) rather than the number of stages as the measurement of CVF, similar results were obtained.

Results from cross-sectional studies have shown associations between homocysteine levels and lifestyle-related factors.20,22-24 However, findings are different when analyzed prospectively.49,50 Duncan et al50 found that 6 months of exercise increased homocysteine levels in sedentary adults, whereas Randeva et al51 showed that 6 months of sustained brisk walking for 20 to 60 minutes 3 days a week significantly decreased homocysteine levels and increased CVF in young overweight and obese women with polycystic ovary syndrome, a group at increased risk of premature atherosclerosis. Similarly, a weight-reduction program that included physical activity had a positive effect on the homocysteine levels in obese children.52 Together, these results suggest that modifications in lifestyle-related factors may influence homocysteine levels in a different manner in children and adolescents than in adults.

The results from the present study should be interpreted with caution because of the limitations of the cross-sectional design; that is, direction of causality cannot be determined. Elevated homocysteine levels may be simply a marker of an unhealthy lifestyle that is associated with poor exercise capacity. The relationship between homocysteine levels and CVF should be studied prospectively. It must be borne in mind that the subjects in this study were healthy adolescents with no previously diagnosed cardiovascular disorders. Also, our study included a moderate number of participants. The observed power for the sample size was low (0.40), which may have masked the association between CVF and homocysteine levels in the adolescent boys. This warrants further investigation. However, we believe that covariates that may confound the measures of association in our study were appropriately considered and controlled for.

The results of this study suggest that CVF is negatively associated with homocysteine levels in adolescent girls after controlling for potential cofounders including the MTHFR 677C>T genotype. These results should stimulate a debate on whether the metabolism of homocysteine could be one way in which the benefits of high CVF levels are exerted.

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Article Information

Correspondence: Jonatan R. Ruiz, BSc, Department of Medical Physiology, School of Medicine, University of Granada, Avda Madrid 12, 18071 Granada, Spain (ruizj@ugr.es).

Accepted for Publication: September 20, 2006.

Author Contributions:Study concept and design: Ruiz, Sola, Gonzales-Gross, Sjöström, Pietrzik, and Castillo. Acquisition of data: Ruiz, Sola, Gonzales-Gross, Ortega, Garcia-Fuentes, Gutierrez, and Castillo. Analysis and interpretation of data: Ruiz, Sola, Gonzales-Gross, Ortega, and Castillo. Drafting of the manuscript: Ruiz. Critical revision of the manuscript for important intellectual content: Sola, Gonzales-Gross, Ortega, Vicente-Rodriguez, Garcia-Fuentes, Gutierrez, Sjöström, Pietrzik, and Castillo. Statistical analysis: Ruiz. Obtained funding: Gonzales-Gross and Castillo. Administrative, technical, and material support: Gonzales-Gross, Sjöström, and Castillo. Study supervision: Sola, Gonzales-Gross, Sjöström, and Castillo.

Financial Disclosure: None reported.

Funding/Support: This study was supported by fund FIS PI021830 from the Spanish Ministry of Health Instituto de Salud Carlos III. The AVENA study was funded by the Spanish Ministry of Health; FEDER-FSE Funds FIS No. 00/0015; CSD grants 05/UPB32/0, 109/UPB31/03, and 13/UPB20/04; grants (AP2003-2128; AP-2004-2745) from the Spanish Ministry of Education; and scholarships from Panrico SA, Madaus SA, and Procter & Gamble SA.

Acknowledgment: We thank Pilar Carazo, BSc, Remedios Perez, BSc, and Teresa AmigoBSc, for their contributions to the laboratory work; and Olle Carlsson, PhD, from the Unit for Preventive Nutrition, Department of Biosciences and Nutrition at NOVUM, Karolinska Institutet, for statistical assistance.

Virtanen  JKVoutilainen  SAlfthan  G  et al.  Homocysteine as a risk factor for CVD mortality in men with other CVD risk factors: the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study.  J Intern Med 2005;257255- 262Google ScholarCrossref
Homocysteine Studies Collaboration, Homocysteine and risk of ischemic heart disease and stroke: a meta-analysis.  JAMA 2002;2882015- 2022PubMedGoogle ScholarCrossref
Vrentzos  GEPapadakis  JAMalliaraki  N  et al.  Diet, serum homocysteine levels and ischaemic heart disease in a Mediterranean population.  Br J Nutr 2004;911013- 1019PubMedGoogle ScholarCrossref
Ford  ESSmith  SJStroup  DFSteinberg  KKMueller  PWThacker  SB Homocyst(e)ine and cardiovascular disease: a systematic review of the evidence with special emphasis on case-control studies and nested case-control studies.  Int J Epidemiol 2002;3159- 70PubMedGoogle ScholarCrossref
Seshadri  SBeiser  ASelhub  J  et al.  Plasma homocysteine as a risk factor for dementia and Alzheimer's disease.  N Engl J Med 2002;346476- 483PubMedGoogle ScholarCrossref
McLean  RRJacques  PFSelhub  J  et al.  Homocysteine as a predictive factor for hip fracture in older persons.  N Engl J Med 2004;3502042- 2049PubMedGoogle ScholarCrossref
Hague  WM Homocysteine and pregnancy.  Best Pract Res Clin Obstet Gynaecol 2003;17459- 469PubMedGoogle ScholarCrossref
Loscalzo  J The oxidant stress of hyperhomocyst(e)inemia.  J Clin Invest 1996;985- 7PubMedGoogle ScholarCrossref
Welch  GNLoscalzo  J Homocysteine and atherothrombosis.  N Engl J Med 1998;3381042- 1050PubMedGoogle ScholarCrossref
Greenlund  KJSrinivasan  SRXu  JH  et al.  Plasma homocysteine distribution and its association with parental history of coronary artery disease in black and white children: the Bogalusa Heart Study.  Circulation 1999;992144- 2149PubMedGoogle ScholarCrossref
Kark  JDSinnreich  RRosenberg  IHJacques  PFSelhub  J Plasma homocysteine and parental myocardial infarction in young adults in Jerusalem.  Circulation 2002;1052725- 2729PubMedGoogle ScholarCrossref
Hyanek  JStribrny  JSebesta  P  et al.  Diagnostic significance of mild hyperhomocysteinemia in a population of children with parents or grandparents who have peripheral or coronary artery disease [in Czech].  Cas Lek Cesk 1999;138333- 336PubMedGoogle Scholar
Morrison  JAJacobsen  DWSprecher  DLRobinson  KKhoury  PDaniels  SR Serum glutathione in adolescent males predicts parental coronary heart disease.  Circulation 1999;1002244- 2247PubMedGoogle ScholarCrossref
Tonstad  SRefsum  HSivertsen  MChristophersen  BOse  LUeland  PM Relation of total homocysteine and lipid levels in children to premature cardiovascular death in male relatives.  Pediatr Res 1996;4047- 52PubMedGoogle ScholarCrossref
De Laet  CWautrecht  JCBrasseur  D  et al.  Plasma homocysteine concentration in a Belgian school-age population.  Am J Clin Nutr 1999;69968- 972PubMedGoogle Scholar
Gonzalez-Gross  MMarcos  APietrzik  K Nutrition and cognitive impairment in the elderly.  Br J Nutr 2001;86313- 321PubMedGoogle ScholarCrossref
Frosst  PBlom  HJMilos  R  et al.  A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase.  Nat Genet 1995;10111- 113PubMedGoogle ScholarCrossref
Papoutsakis  CYiannakouris  NManios  Y  et al.  Plasma homocysteine levels in Greek children are influenced by an interaction between the methylenetetrahydrofolate reductase C677T genotype and folate status.  J Nutr 2005;135383- 388PubMedGoogle Scholar
Balasa  VVGruppo  RAGlueck  CJ  et al.  The relationship of mutations in the MTHFR, prothrombin, and PAI-1 genes to plasma levels of homocysteine, prothrombin, and PAI-1 in children and adults.  Thromb Haemost 1999;81739- 744PubMedGoogle Scholar
Jacques  PFBostom  AGWilson  PWRich  SRosenberg  IHSelhub  J Determinants of plasma total homocysteine concentration in the Framingham Offspring cohort.  Am J Clin Nutr 2001;73613- 621PubMedGoogle Scholar
Selhub  JJacques  PFWilson  PWRush  DRosenberg  IH Vitamin status and intake as primary determinants of homocysteinemia in an elderly population.  JAMA 1993;2702693- 2698PubMedGoogle ScholarCrossref
Nygard  ORefsum  HUeland  PMVollset  SE Major lifestyle determinants of plasma total homocysteine distribution: the Hordaland Homocysteine Study.  Am J Clin Nutr 1998;67263- 270PubMedGoogle Scholar
Silaste  MLRantala  MAlfthan  GAro  AKesaniemi  YA Plasma homocysteine concentration is decreased by dietary intervention.  Br J Nutr 2003;89295- 301PubMedGoogle ScholarCrossref
Chrysohoou  CPanagiotakos  DBPitsavos  C  et al.  The associations between smoking, physical activity, dietary habits and plasma homocysteine levels in cardiovascular disease-free people: the “ATTICA” study.  Vasc Med 2004;9117- 123PubMedGoogle ScholarCrossref
Myers  JPrakash  MFroelicher  VDo  DPartington  SAtwood  JE Exercise capacity and mortality among men referred for exercise testing.  N Engl J Med 2002;346793- 801PubMedGoogle ScholarCrossref
LaMonte  MJBarlow  CEJurca  RKampert  JBChurch  TSBlair  SN Cardiorespiratory fitness is inversely associated with the incidence of metabolic syndrome: a prospective study of men and women.  Circulation 2005;112505- 512Google ScholarCrossref
Kuo  HKYen  CJBean  JF Levels of homocysteine are inversely associated with cardiovascular fitness in women, but not in men: data from the National Health and Nutrition Examination Survey 1999-2002.  J Intern Med 2005;258328- 335PubMedGoogle ScholarCrossref
Mesa  JLOrtega  FBRuiz  JRCastillo  MJHurtig Wennlöf  AGutiérrez  A The importance of cardiorespiratory fitness for healthy metabolic traits in children and adolescents: the AVENA Study.  J Public Health 2006;14178- 180Google ScholarCrossref
Ruiz  JROrtega  FBMeusel  DHarro  MOja  PSjöström  M Cardiorespiratory fitness is associated with features of metabolic risk factors in children: should cardiorespiratory fitness be assessed in a European health monitoring system? the European Youth Heart Study.  J Public Health 2006;1494- 102Google ScholarCrossref
Mesa  JLRuiz  JROrtega  FB  et al.  Aerobic physical fitness in relation to blood lipids and fasting glycaemia in adolescents: Influence of weight status.  Nutr Metab Cardiovasc Dis 2006;16285- 293PubMedGoogle ScholarCrossref
Gonzalez-Gross  MCastillo  MJMoreno  L  et al.  Feeding and assessment of nutritional status of Spanish adolescents (AVENA Study): evaluation of risks and interventional proposal: I, methodology [in Spanish].  Nutr Hosp 2003;1815- 28PubMedGoogle Scholar
Moreno  LAMesana  MIFleta  J  et al.  Overweight, obesity and body fat composition in Spanish adolescents: The AVENA Study.  Ann Nutr Metab 2005;4971- 76Google ScholarCrossref
Ruiz  JROrtega  FBMoreno  LA  et al.  Serum lipid and lipoprotein distributions of Spanish adolescents: the AVENA Study.  Soz Praventivmed 2006;5199- 109Google ScholarCrossref
Sociedad Española de Epidemiología, La Medición de la Clase Social en Ciencias de la Salud: Informe de un Grupo de Trabajo de la Sociedad Española de Epidemiología.  Barcelona, Spain SG Editores1995;
Moreno  LARodríguez  GGuillén  JRabanaque  MJLeón  JFAriño  A Anthropometric measurements in both sides of the body in the assessment of nutritional status in prepubertal children.  Eur J Clin Nutr 2002;561208- 1215PubMedGoogle ScholarCrossref
Moreno  LAMesana  MIGonzález-Gross  M  et al.  Anthropometric body fat composition reference values in Spanish adolescents: the AVENA Study.  Eur J Clin Nutr 2006;60191- 196PubMedGoogle ScholarCrossref
Moreno  LAJoyanes  MMesana  MI  et al.  Harmonization of anthropometric measurements for a multicenter nutrition survey in Spanish adolescents.  Nutrition 2003;19481- 486PubMedGoogle ScholarCrossref
Rodriguez  GMoreno  LABlay  MG  et al.  Body fat measurement in adolescents: comparison of skinfold thickness equations with dual-energy x-ray absorptiometry.  Eur J Clin Nutr 2005;591158- 1166Google ScholarCrossref
Tanner  JMWhitehouse  RH Clinical longitudinal standards for height, weight, height velocity and stages of puberty.  Arch Dis Child 1976;51170- 179PubMedGoogle ScholarCrossref
Leger  LLambert  AGoulet  ARowan  CDinelle  Y Aerobic capacity of 6- to 17-year-old Quebecois: 20-meter shuttle run test with 1 minute stages [in French].  Can J Appl Sport Sci 1984;964- 69PubMedGoogle Scholar
Leger  LAMercier  DGadoury  CLambert  J The multistage 20 metre shuttle run test for aerobic fitness.  J Sports Sci 1988;693- 101PubMedGoogle ScholarCrossref
Liu  NYSPlowman  SALooney  MA The reliability and validity of the 20-meter shuttle test in American students 12 to 15 years old.  Res Q Exerc Sport 1992;63360- 365PubMedGoogle ScholarCrossref
Willems  HPBos  GMGerrits  WBden Heijer  MVloet  SBlom  HJ Acidic citrate stabilizes blood samples for assay of total homocysteine.  Clin Chem 1998;44342- 345PubMedGoogle Scholar
Higuchi  RErlich  Hed Simple and rapid preparation of samples for PCR.  PCR Technology. New York, NY Stockton Press1989;31- 37Google Scholar
Taylor  HLBuskirk  EHenschel  A Maximal oxygen uptake as an objective measure of cardio-respiratory performance.  J Appl Physiol 1955;873- 80Google Scholar
Reed  KEWarburton  DELewanczuk  RZ  et al.  Arterial compliance in young children: the role of aerobic fitness.  Eur J Cardiovasc Prev Rehabil 2005;12492- 497PubMedGoogle ScholarCrossref
Jakubowski  H Homocysteine thiolactone: metabolic origin and protein homocysteinylation in humans.  J Nutr 2000;130377S- 381SPubMedGoogle Scholar
Kado  DMBucur  ASelhub  JRowe  JWSeeman  T Homocysteine levels and decline in physical function: MacArthur Studies of Successful Aging.  Am J Med 2002;113537- 542PubMedGoogle ScholarCrossref
Husemoen  LLThomsen  TFFenger  MJorgensen  T Changes in lifestyle and total homocysteine in relation to MTHFR(C677T) genotype: the Inter99 study.  Eur J Clin Nutr 2006;60614- 622PubMedGoogle ScholarCrossref
Duncan  GEPerri  MGAnton  SD  et al.  Effects of exercise on emerging and traditional cardiovascular risk factors.  Prev Med 2004;39894- 902PubMedGoogle ScholarCrossref
Randeva  HSLewandowski  KCDrzewoski  J  et al.  Exercise decreases plasma total homocysteine in overweight young women with polycystic ovary syndrome.  J Clin Endocrinol Metab 2002;874496- 4501PubMedGoogle ScholarCrossref
Gallistl  SSudi  KMErwa  WAigner  RBorkenstein  M Determinants of homocysteine during weight reduction in obese children and adolescents.  Metabolism 2001;501220- 1223PubMedGoogle ScholarCrossref