Body mass index , blood pressure , and serum cholesterol in young Swiss men : an analysis on 56784 army conscripts

Questions under study: This study aimed to investigate the prevalence of excess bodyweight and high blood pressure in young Swiss men and to evaluate the associations of these disorders with serum cholesterol in this important population. Methods: The study investigated a large cohort of 56784 Swiss army conscripts aged 18–25 years from 2004 through to 2007. Results: From the investigated men, 2231 (3.9%) were underweight with a body mass index (BMI) <18.5 kg/m2, 42681 (75.2%) were normal weight (BMI 18.5–24.9 kg/m2), 9562 (16.8%) were overweight (BMI 25.0–29.9 kg/m2), and 1811 (3.2%), 402 (0.7%) and 96 (0.2%) had obesity classes I, II or III, respectively. The prevalence of blood pressure within the hypertensive range significantly increased through these categories of BMI (12.5%, 23.9%, 37.6%, 49.7%, 56.7%, and 54.2%), as did serum levels of cholesterol (3.8 ± 0.6, 4.0 ± 0.7, 4.4 ± 0.8, 4.7 ± 0.9, 4.7 ± 0.9, and 4.8 ± 1.1 mmol/l). Serum cholesterol also increased through categories of blood pressure (4.0 ± 0.7mmol/l in normotensive subjects and 4.1 ± 0.7, 4.2 ± 0.8, and 4.5 ± 0.9 in those with blood pressure in the ranges of pre-hypertension, and hypertension stages 1 and 2, respectively); excess body weight and blood pressure in the hypertensive range were associated with serum cholesterol in a mutually independent manner. Conclusions: Prevalence rates of excess bodyweight and of elevated blood pressure are high in young Swiss men, and these entities are strongly interrelated. Excess body weight and high blood pressure are independently associated with high serum cholesterol in this population. Excess bodyweight and associated risk factors should receive increased attention in young Swiss men.


Summary
Western societies are facing an epidemic of obesity, with major implications on health care systems [1].The prevention and treatment of obesity is a paramount aspect of cardiovascular disease prevention in clinical practice [2].However, the prevalence rates of excess bodyweight and obesity have been increasing in adults and also in adolescents during the last several decades [3][4][5][6][7][8][9][10][11].
Whereas the prevalence of excess body weight is typically lower among adolescents than among adults [12], exposure to the obese state early in life strongly increases the risk of obesityrelated complications such as diabetes mellitus or cardiovascular disease in middle age [13].Further, obesity during the second decade of life is an important predictor of adult obesity [14][15][16].
Yo ung individuals aged around 20 years are a particularly important group with respect to the study of cardiovascular risk factors.This is the age of the transition from adolescence to young adulthood where, in parallel to changes in working and social status, alterations in life-style typically occur.Interventions at this age may be particularly effective to decrease the burden of cardiovascular disease later in life.
The association of a high BMI with cardiovascular disease is at least partly explained by the association of BMI with cardiovascular risk factors such as hypertension and elevated serum cholesterol [17].However, hardly any previous studies have addressed the associations of excess body weight with hypertension in adolescents or

Introduction
Financial support / Conflicts of Interest: NONE.
young adults, and no data are available on the association of serum cholesterol with body weight in this age cohort.
This study therefore aimed to provide current estimates of the prevalence of excess bodyweight and obesity, as well as of elevated blood pressure, in a large unselected series of young men undergoing medical examination prior to entering service in the Swiss army.This study also aimed to evaluate the associations of these entities with each other and with serum levels of cholesterol.

Patients and methods
The data for the present investigation were extracted from the database containing the Swiss conscription health examinations.Military service is compulsory for young men in Switzerland, and with conscription (usually between the ages of 18 and 25 years) young Swiss men are subjected to a thorough medical investigation.The database of these conscription health examinations contains information on 95% of the age cohort; information is missing in less than 5% due to severe illness precluding individuals from participation in the conscription examination.In such cases, a written medical record from a physician is required.
Starting from January 1, 2004, a comprehensive medical examination was introduced for Swiss conscripts, which includes a voluntary laboratory testing (to which more than half of the conscripts consent).Blood was taken at the conscription centres in the fasting or in the non-fasting state, and was shipped to a laboratory centre in Basel, Switzerland, to be tested generally within 12 hours of sampling.To tal cholesterol was measured by enzymatic assay on Cobas Integra 800 (Roche, Rotkreuz Switzerland) [18] and Bayer Advia 1650 (Siemens Diagnostics, Zurich Switzerland) [19].In the main analysis, 56 784 conscripts for whom serum cholesterol was measured from 2004 through to 2007 were included.Including participants who refused blood cholesterol measurement, anthropometric data and blood pressure are also reported for a total of 101 844 conscripts.Written informed consent was obtained from all study participants.

Statistical analysis
Continuous study variables were tested for normal distribution by inspection of histograms and by using Kolmogorov-Smirnov tests.For two-group comparisons, differences in study variables for categorical variables were tested for statistical significance with Chi-squared tests, and for continuous variables with Mann-Whitney-U tests.For trends over categories we used Mantel-Haenszel Chi-squared tests for categorical variables and ordered Jonckheere-Terpstra tests for continuous variables.Analysis of covariance (ANCOVA) was performed using a general linear model approach to test independent associations of continuous and dichotomous variables with continuous variables for statistical significance (in particular, the mutually independent impact of BMI and high blood pressure on cholesterol was derived from an ANCOVA model).Linear regression models were built to study the association between continuous variables.Prior to being entered into these models variables were z-transformed, and standardized beta-coefficients are reported together with 95% confidence intervals and with corresponding p-values.Results are given as mean ± standard deviation if not denoted otherwise.P-values <0.05 were considered significant.All statistical analyses were performed with the software package SPSS 11.0 for Windows (Chicago, IL, USA).
The study is in accordance with the Helsinki Declaration and adheres to the legal requirements of the study country.

Association between BMI and blood pressure
As summarized in table 2, systolic as well as diastolic blood pressure strongly and significantly increased through the categories of BMI (ptrend <0.001 for both).Concordantly, the prevalence of high blood pressure significantly increased through these BMI categories (fig.1; ptrend <0.001).

BMI, blood pressure and serum cholesterol
Mean serum cholesterol in the study population was 4.1 ± 0.8 mmol/l; it was >5.2 mmol/l in 6.9% of the investigated men and >6.2 mmol/l in 0.9%.Serum cholesterol increased significantly by 20 From the 44913 normal-weight men 10484 had blood pressure values in the hypertensive range (≥140/90 mm Hg) according to JNC VII guidelines, and from the 11871 men who were overweight or obese, 4776 had blood pressure ≥140/90 mm Hg. Figure 2 shows serum cholesterol values with respect to both the presence of excess body weight and high blood pressure: Serum cholesterol was lowest (4.0 ± 0.7 mmol/l) in normal-weight subjects with blood pressure <140/90 mm Hg, it was significantly higher in normal-weight subjects with blood pressure ≥140/90 mm Hg (4.1 ± 0.7 mmol/l; p <0.001) as well as in subjects with blood pressure <140/ 90 mm Hg who were overweight or obese (4.4 ± 0.8 mmol/l; p <0.001), and highest in subjects with blood pressure ≥140/90 mm Hg who were overweight or obese (4.5 ± 0.8 mmol/l; p <0.001 for the comparison with all other groups).Analysis of covariance, after adjustment for age, confirmed that both excess bodyweight, or obesity (F = 2407.1;p <0.001), and the presence of blood pressure ≥140/90 mm Hg (F = 141.8;p <0.001) were associated with serum cholesterol in a mutually independent manner.
Ta ble 4 summarizes the results of linear regression analyses modelling associations between serum cholesterol, BMI, and systolic as well as diastolic blood pressure.These models showed that the association between serum cholesterol and BMI was stronger than that between serum cholesterol and blood pressure.However, the associations between serum cholesterol and systolic as well as diastolic blood pressure remained significant after adjustment for BMI.Ta king systolic and diastolic blood pressures into account separately revealed that systolic blood pressure was not associated with serum cholesterol independently from diastolic blood pressure, whereas diastolic blood pressure was associated with serum cholesterol independently of systolic blood pressure.

Discussion
From the current data it is concluded that the prevalence of excess body weight and of blood pressure in the hypertensive range is high among young Swiss men undergoing medical conscript examinations, and that excess body weight and blood pressure in the hypertensive range are strongly associated with each other and with high serum cholesterol in this population.
A trend of increasing body weight and obesity is an almost worldwide phenomenon.However, available data on the prevalence of obesity in adolescence or young adulthood shows considerable geographical variation between Europe and the United States, as well as throughout Europe, with the highest rates of obesity in the United States, followed by eastern and southern European countries [21][22][23][24][25][26][27][28][29][30].For Switzerland, estimates of the prevalence of obesity in adolescence are available from 1993 [12,31] and from 2003 [31] however these estimates were based on self-reported weight and height values.The 2003 report described a 15% prevalence of excess bodyweight and obesity in a combined study sample of 20 year old military recruits and subjects of that age from the general community.Our present analysis from the period 2004-2007 was based on measured body weight and height and found a higher prevalence of 20.9% for excess bodyweight and obesity.Of note, the prevalence of excess body weight and obesity in our study population was similar to that found in primary school children in Switzerland [32].
BMI in late adolescence is an important predictor of both premature CAD and stroke [13,33].This may in part be explained by the strong association of excess body weight with blood pressure that was observed in the current investigation.
Indeed, only a minority of the investigated men had a blood pressure that was normal according to JNC VII guidelines; almost two thirds had blood pressure in the pre-hypertension range.Data on the prevalence of abnormal blood pressure in young men are scarce.An investigation on military conscripts from Israel had found an extremely high prevalence of pre-hypertension in adolescents 16.5-19 years of age [34], in which 56.8% of male subjects were pre-hypertensive.As in the current investigation, the prevalence of pre-hypertension was significantly higher in obese or overweight subjects in the study from Israel.
Similar to the current data on the prevalence of excess body weight and obesity, our results on the prevalence of high blood pressure in Swiss conscripts call for action.Hypertension as well as pre-hypertension in adolescence predict hypertension in adults [35], and high blood pressure is a crucial modifiable risk factor for cardiovascular disease.The association between blood pressure and the risk of cardiovascular morbidity and mortality is consistent and continuous [20].
Hypertension is associated with obesity not only in adults, but also in children and adolescents [36].A recent study from Sweden found that hypertension in young adulthood (diagnosed during conscript examinations) is associated with an increased risk of receiving disability pension later in life [37].Obesity may have independent associations with blood pressure, but the entities are also related through physical inactivity and nutrition, which emphasizes the need to reduce the risks conferred by obesity and hypertension through lifestyle interventions.Concordant with our data Aeberli et al. demonstrated an association between blood pressure and body weight in Swiss children and adolescents [38].That investigation also points to a possible relationship of hypertension or obesity with nutritional factors.Of note, the association between BMI and blood pressure in our study was quite strong: systolic as well as diastolic blood pressure differed by almost 10% between the extreme groups of BMI, an effect size which is in the same order of magnitude as that obtained with current antihypertensive therapy [39].
High levels of serum cholesterol are a major risk factor for cardiovascular disease [40].Serum cholesterol in our investigation was around 20% higher in obese subjects than in those with low or normal BMI.As a 1 mg/dl increase of LDL cholesterol confers more than a 1% increase in cardiovascular risk [41], this association between BMI and serum cholesterol is clinically relevant.A 2004 examination of Swiss army conscripts has shown that 9.1% of the young men had cholesterol values above the limit (5.2 mmol/l) which is judged as desirable by the National Cholesterol Education Programme's updated clinical guidelines [42], and 1.4% had significantly elevated serum cholesterol levels >6.2 mmol/l.The overall serum cholesterol levels were somewhat lower in the current investigation from the period 2004-2007; however, our data show that serum choles- Standardized beta-coefficients are given together with 95% confidence intervals.Model 1 is unadjusted.Model 2 adjusts for BMI.Model 3 includes three of the four variables BMI, serum cholesterol, systolic blood pressure and diastolic blood pressure as independent variables whereas the respective fourth of these variables serves as dependent variable in the regression models.

Ta ble 4
Results from linear regression analyses.
terol significantly increases with both increasing body weight and increasing blood pressure.Indeed among obese men, one in four had serum cholesterol >5.2 mmol/l.Excess body weight and high blood pressure were associated with each other and linear regression analyses revealed that the association between BMI and serum cholesterol was stronger than that between blood pressure and serum cholesterol.However, excess body weight and high blood pressure were associated with serum cholesterol independently from each other.Important strengths of this study are that the data are from the database providing the most recent prevalence estimate of body weight and obesity, hypertension, and serum cholesterol in young males in Switzerland, and also the large number of subjects included in the analysis.As discussed above, the key results were statistically significant and quantitatively of a clinically important order of magnitude.Due to the large sample size even much smaller between-group differences would have been statistically significant.Some limitations should also be considered.Most importantly, data is only provided for young men, because conscription is not compulsory for women in Switzerland.Further, HDL cholesterol levels were not available.To tal cholesterol was measured in random blood samples and not in fasting serum samples.However, this should not have biased the data, because serum levels of total cholesterol are not strongly influenced by prior food intake [43].Further, as only a single-occasion blood pressure measurement was available, an overestimation of the prevalence of high blood pressure in our study is possible, even though our data are in agreement with a report on the pre-valence of elevated blood pressure in young men from Israel [34].However, the striking associations between blood pressure and BMI or serum cholesterol indicate that the blood pressure measurements obtained in our study are indeed relevant for the cardiovascular risk estimation of the studied population.Most importantly, also "white coat hypertension" is associated with target organ damage [44].
In conclusion, the study found that excess body weight and high blood pressure are highly prevalent and closely associated with each other as well as with serum cholesterol in young Swiss men.Risk stratification and targeted risk intervention in adolescents and young adults is mandatory.Though the incidence of clinical events of atherosclerotic disease is very low in this age group, atherosclerotic plaques typically develop at young age, and it is at young age where long-term prevention might prove most effective [42].Indeed, in older adults increased BMI is already associated with a considerable amount of morbidity and disability [45].Data from conscription health examinations could be a useful tool for public health monitoring and timely risk intervention.
NW, no HT denotes the group with normal weight that does not have hypertension, NW, HT denotes the normal weight group with hypertension, OV/OB, no HT denotes the overweight / obese group without hypertension, and OV/OB, HT denotes the group with overweight / obesity plus hypertension.