Abstract
OBJECTIVE:
The authors previously reported that adult South Asian immigrants to Canada have an increased risk of cardiovascular disease (CVD) compared to their European and Chinese counterparts. It is unknown whether these ethnic differences also exist among adolescents, and whether they are related to diet and lifestyle. The objective of the present study was to assess the prevalence of CVD risk factors among apparently healthy adolescents in the three largest ethnic population groups in Canada (European, South Asian and Chinese).
METHODS:
A cross-sectional study among secondary school students in the Greater Toronto Area was undertaken. A total of 203 adolescents from 62 GTA secondary schools were recruited (48% Europeans, 35% Chinese and 18% South Asians) with a mean age of 17.3±1 years; 72% were female.
RESULTS:
Similar to adults, South Asian adolescents have increased rates of CVD risk factors compared with their European and Chinese peers, including higher prevalence of low high-density lipoprotein levels (P=0.001), high triglycerides (P=0.006) and high triglyceride/high-density lipoprotein levels (P<0.001), despite no significant differences in dietary intake among the ethnic groups. European adolescents had higher rates of self-reported intensity of physical activity (P=0.002) than their Chinese or South Asian peers.
CONCLUSIONS:
Similar to adult data, South Asian adolescents have comparably higher rates of CVD risk factors compared with their European or Chinese peers, which could partly be attributed to lower physical activity in South Asian adolescents. Whether the findings in these selected samples of healthy adolescents can be generalized to their respective populations requires further validation.
Keywords: Adolescents, Cardiovascular disease, Ethnicity, Risk factors
Abstract
OBJECTIF :
Nous avons déjà rendu compte que les immigrants adultes qui partent d’Asie du Sud pour s’installer Canada présentent un risque de maladie cardiovasculaire (MCV) plus élevé que leurs homologues européens et chinois. On ne sait pas si ces différences ethniques s’observent également chez les adolescents et si elles sont liées au régime et au mode de vie. Les auteurs s’étaient donné comme objectif d’évaluer la prévalence de facteurs de risque de MCV chez des adolescents apparemment en santé des trois plus grands groupes de population ethnique du Canada (Europe, Asie du Sud et Chine).
MÉTHODOLOGIE :
Les auteurs ont entrepris une étude transversale auprès d’élèves du secondaire de la grande région de Toronto (GRT). Au total, ils ont recruté 203 adolescents de 62 écoles secondaires de la GRT (48 % d’Européens, 35 % de Chinois et 18 % de Sud-Asiatiques) d’un âge moyen de 17,3±1 ans, dont 72 % de sexe féminin.
RÉSULTATS :
Tout comme les adultes, les adolescents sud-asiatiques présentent un taux plus élevé de facteurs de risque de MCV que leurs homologues européens et chinois, y compris une plus forte prévalence de lipoprotéines de haute densité (HDL) faibles (P=0,001), de triglycérides (TG) élevés (P=0,006), et de ratio TG/HDL élevé (P<0,001), malgré une différence non significative de l’apport diététique entre les groupes ethniques. Les adolescents européens présentaient un taux plus élevé d’intensité autodéclarée d’activité physique (P=0,002) que leurs camarades chinois ou sud-asiatiques.
CONCLUSIONS:
Tout comme l’indiquent les données SHARE chez les adultes, les adolescents sud-asiatiques présentent un taux de facteurs de risque de MCV comparativement plus élevé que leurs homologues européens ou chinois, qui peut être partiellement attribué à un taux moins élevé d’activités physiques chez les adolescents sud-asiatiques. Pour savoir s’il est possible de généraliser les observations auprès de ces échantillons d’adolescents en santé au sein de leur population respective, il faudra procéder à des validations plus approfondies.
Unlike in adults, about whom much has been learned with respect to the pathogenesis of atherogenic cardiovascular disease (CVD), there remains a relative lack of basic and clinical data on adolescents. Recent data have begun to suggest, however, that the origins of CVD can be traced back to childhood (1,2). The risk for future development of CVD in children with abnormal values for cardiovascular risk factors (RF) and metabolic syndrome (MetS) is high, and early indicators for CVD, such as carotid artery intimal-media thickness and atherosclerotic plaques, have been shown to develop in childhood (3,4).
Although the details of the transition from CVD RF in adolescents to CVD in adults are not clear, compelling evidence indicates that the pathological processes associated with CVD can be tracked from adolescence to adulthood (5,6). The National Health and Nutrition Examination Survey (NHANES) reported a high prevalence of CVD RF among adolescents, with about half of the participants having at least one elevated RF, and an overall MetS prevalence of 8.6% (7).
Increasing evidence indicates that CVD rates and lifestyle factors vary greatly between ethnic groups in Canada (8–12). Adoption of a westernized lifestyle has different effects on metabolic and vascular dysfunction, with adult South Asians having a higher prevalence of coronary heart disease and cardiovascular mortality compared with Europeans (13). Although the prevalence of CVD RF has been studied in a multiethnic adolescent population in the United States (consisting of Caucasian, Hispanic and African-American youths) (7), studies among Canadian multi-ethnic adolescents, especially among Chinese, Europeans and South Asians, are lacking. More than half of the population of Canada’s largest city, Toronto, is made up of immigrants, while another quarter is second-generation immigrants. The majority of these immigrants (58.4%) arrive from Asia, with the greatest number from China and South Asia (14). Our previous study confirmed that ethnic differences exist in the rates of CVD, and specifically that Canadian adults of South Asian origin have higher rates of CVD compared with Canadians of European and Chinese origin, probably because of an increased risk of thrombogenesis (9,10). In another study of a multiethnic sample, we found elevated rates of MetS among adolescents (15), hence making them prone to future risk of CVD.
Thus the purpose of the present pilot study was to identify and compare the presence of CVD RF, including diet and lifestyle, among healthy multiethnic adolescents belonging to the three largest ethnic groups (Europeans, Chinese, South Asians) in the Greater Toronto Area (GTA). Detecting high-risk ethnic groups and CVD RF in adolescence could help initiate long-term interventions earlier in life; particularly diet, weight control and lifestyle modifications that can halt the progression of future atherogenic CVD (16,17).
METHODS
Participants
Two hundred three students (146 females and 57 males) from 62 GTA high schools were recruited as a convenience sample to participate in this cross-sectional study. Participants were derived from the University of Toronto Mentorship Program and were selected to this program because of their interest in nutrition and medical research.
The inclusion criteria were adolescent age (15 to 19 years of age), high school student status, Canadian-born, healthy individuals with both parents belonging to the same ethnicity and living in Canada for more than five years. Canadians were classified as Chinese if their ancestors originated from China, Taiwan or Hong Kong; South Asian if their ancestors originated from India, Pakistan, Sri Lanka or Bangladesh; and European if their ancestors originated from any country in Europe. The participants were selected because of their interest in an academically-oriented program, and it is not known whether these subjects represented the racial and socioeconomic mix within the general population or within the ethnic groups studied.
The number of individuals selected from each ethnic group was based on the average population profile of these groups living within the GTA. Sample size calculations suggested that 30 participants per ethnic group would provide over 80% power to detect differences in the mean of low-density lipoprotein (LDL) of at least 0.6 mmol/L (assuming a standard deviation of 0.8 mmol/L) between each ethnic group. This sample size would also provide sufficiently high power to detect important differences in cardiovascular risk factors between ethnic groups.
Individuals with diabetes or other chronic illness were excluded. This study (‘little s.h.a.r.e.’, Study of Health of Adolescents and Role of Ethnicity) is an extension of ‘large SHARE’ (Study of Health Assessment and Risk in Ethnic Groups) conducted in an adult population with the same ethnic backgrounds. The present study was performed at the Clinical Nutrition and Risk Factor Modification Centre, St Michael’s Hospital, and approved by the St Michael’s Hospital Research Ethics Board. All subjects gave written informed consent before starting the study.
Anthropometric characteristics
Each participant’s fasting body weight was measured to the nearest 0.1 kg using a calibrated SECA Delta model 707 digital scale (Vogel & Halke GmbH & Co, Germany) while the subject wore light clothing and no shoes. Height was measured to the nearest 0.5 cm using a standardized, wall-mounted stadiometer (Perspective Enterprises, USA) with the subject barefooted and their head held in the ‘Frankfort horizontal’ position. Waist circumference was measured while standing to the nearest 0.5 cm, after gently exhaling, as the minimal circumference measurable on the horizontal plane between the lowest portion of the rib cage and iliac crest using a flexible non-stretchable measuring tape (18). Hip circumferences were measured to the nearest 0.5 cm at the widest point. Total body fat (%) was assessed by the near-infrared method with FUTREX-5000 (Futrex Inc, USA).
Blood pressure
Blood pressure was taken three consecutive times, each at least 2 min apart, using the HEM-907 (Omron Healthcare Inc, USA) digital blood pressure monitor with an appropriate size cuff, from the dominant arm, with the subject seated quietly for at least 5 min. The average of three readings was recorded for analysis.
Biochemical measurements
The subjects were tested in the morning after 10 h to 12 h of fasting. A 35 μL capillary blood sample was obtained by finger prick in heparin coated capillary glass tubes. Blood samples were analyzed by the desktop Cholestech LDX Analyzer (Cholestech Corporation, USA) which combines enzymatic methodology and solid-phase technology to measure total cholesterol (TC), high-density lipoprotein (HDL), LDL (calculated), triglycerides (TG) and glucose. The Cholestech analyzers are often used in population studies and are considered a good screening tool. According to the manufacturer, the Cholestech LDX Analyzer meets all relevant National Cholesterol Education Program (NCEP) guidelines and is certified by the Centers for Disease Control and Prevention (CDC) Cholesterol Reference Method Laboratory Network (19), and has been validated for point-of-care lipid measurements in clinical practice (20).
Elevated blood pressure, impaired fasting glucose, central obesity as assessed by waist circumference, metabolic syndrome and dyslipidemia (raised TG or reduced HDL) were reported according to the International Diabetes Federation (IDF) definition, where adult criteria are applied for children ≥16 years of age (1).
Diet and physical activity
To assess participants’ dietary intakes, three-day food records were analyzed by using Food Processor Nutrition Analysis software, version 7.1 (ESHA Research, USA). Physical activity was assessed retrospectively using a questionnaire with five ordinal categories of intensity of physical exercise.
Statistical analysis
Statistical analysis was undertaken with SAS version 8.02 (SAS Institute Inc., USA) and SPSS release 15.0 (SPSS Inc., USA). The results were expressed as the mean ± SD, with the level of significance at P<0.05. Parametric analyses were conducted following a comparison of the sampling distribution to a normal distribution (Shapiro-Wilk and Kolmogorov-Smirnov tests). The tests did not reject the null hypothesis at α=0.05.
As male adolescents have different anthropometric and biochemical characteristics from females (21), separate analyses were conducted for both genders, as well as analysis for the whole group. One-way ANOVA, adjusted for multiple comparisons with the post hoc Tukey honestly significant difference test, was used to assess differences in anthropometric characteristics, blood pressure and biochemical measurements among the ethnic groups. For dietary data having large SD due to high individual variability, and for the ordinal physical activity scale, an overall comparison was performed using the non-parametric Kruskal-Wallis H test with subsequent pairwise comparisons with the non-parametric Mann-Whitney U test. Categorical data (gender, number of adolescents with at least one disordered MetS indicator) were analyzed using the χ2 test.
RESULTS
Population characteristics
The study population included 203 multiethnic adolescents with a mean age of 17.3±1 years; 146 (72%) were female (Table 1). Proportionately, 80% of the students were from public schools, 14% from catholic schools and 6% from private schools, representing a typical school profile in Ontario. The ethnic distribution of the studied population was 48% Europeans, 35% Chinese and 18% South Asians, approximately reflecting the population makeup of the GTA.
TABLE 1.
Population characteristics, anthropometric measurements, and blood pressure data
| Parameter | Europeans n=98 | Chinese n=68 | South Asians n=37 | ANOVA P value |
|---|---|---|---|---|
| Population characteristics | ||||
| Age (years) | 17.2±1.0 | 17.4±0.7 | 17.4±0.8 | 0.35 |
| Males | 17.7±0.8 | 17.4±0.7 | 17.7±0.9 | 0.45 |
| Females | 17.1±1.01 | 17.3±0.7 | 17.3±0.8 | 0.30 |
| Female sex, n (%) | 78 (79.6) | 43 (63.2) | 25 (67.6) | 0.06 |
| Anthropometric measurements | ||||
| Weight (kg) | 64.1±13.5a | 57.2±10.1b | 58.8±13.0 | 0.001 |
| Males | 77.6±13.1a | 63.7±10.2b | 67.9±13.7 | 0.001 |
| Females | 60.6±11.3a | 53.5±8.1b | 54.4±10.3b | 0.001 |
| Height (cm) | 167±8.2a | 164±8.7b | 165±8.0 | 0.03 |
| Males | 175±7.9 | 172±6.2 | 174±3.4 | 0.28 |
| Females | 165±7.0a | 159±5.8b | 161±5.1b | <0.001 |
| Body mass index (kg/m2) | 22.8±4.0a | 21.2±2.7b | 21.5±3.8 | 0.01 |
| Males | 25.3±4.4a | 21.4±2.7b | 22.3±4.1 | 0.002 |
| Females | 21.2±3.6 | 21.1±2.7 | 21.1±3.7 | 0.17 |
| Waist circumference (cm) | 72.3±10.0a | 68.7±6.7b | 69.7±9.1 | 0.03 |
| Males | 81.8±9.1a | 71.7±6.4b | 75.2±10.2 | 0.001 |
| Females | 70.0±8.8 | 67.0±6.3 | 67.1±7.4 | 0.08 |
| Central obesity, n (%) | 10 (10.2) | 1 (1.5) | 3 (8.1) | 0.09 |
| Waist-hip ratio | 0.73±0.06 | 0.74±0.05 | 0.74±0.07 | 0.44 |
| Males | 0.79±0.06 | 0.77±0.05 | 0.80±0.07 | 0.19 |
| Females | 0.71±0.05 | 0.73±0.05 | 0.71±0.05 | 0.30 |
| Body fat (%) | 23.5±7.3 | 22.6±7.7 | 22.9±8.4 | 0.72 |
| Males | 17.5±8.2 | 14.4±5.1 | 14.4±7.7 | 0.30 |
| Females | 25.1±6.3 | 26.9±4.5 | 26.6±5.6 | 0.18 |
| Blood pressure | ||||
| Systolic blood pressure (mmHg) | 107±11 | 106±11 | 106±11 | 0.95 |
| Males | 115±10 | 114±9 | 115±9 | 0.94 |
| Females | 104±10 | 102±10 | 102±10 | 0.27 |
| Raised SBP, n (%) | 3 (3.1) | 2 (2.9) | 1 (2.7) | 0.99 |
| Diastolic blood pressure (mmHg) | 69±7 | 70±8 | 69±8 | 0.53 |
| Males | 72±6 | 74±8 | 74±6 | 0.59 |
| Females | 69±7 | 68±7 | 66±8 | 0.38 |
| Raised DBP, n (%) | 1 (1.0) | 1 (1.5) | 0 | 0.77 |
Data represented as mean ± SD, unless otherwise indicated. ab Different superscript letters across the rows denote pairwise significant differences between the ethnic groups using post hoc Tukey honestly significant difference test (P<0.05). DBP Diastolic blood pressure; SBP Systolic blood pressure
Anthropometric characteristics
Significant differences were noted among the ethnic groups in their anthropometric characteristics. Weight, height, body mass index (BMI) and waist circumference in European adolescents were significantly higher than in Chinese adolescents, but waist/hip ratio and percent body fat did not differ (Table 1). Differences in BMI and waist circumference were attributed entirely to the male subjects.
Blood pressure
Systolic and diastolic blood pressure did not differ among the groups (Table 1).
Biochemical CVD risk factors
There were no differences among the groups in fasting blood glucose (FBG) although the prevalence of impaired FBG was insignificantly higher among European (6.1%) and South Asian (8.1%) adolescents (Table 2).
TABLE 2.
Biochemical measurements
| Parameter | Europeans n=98 | Chinese n=68 | South Asians n=37 | ANOVA P value |
|---|---|---|---|---|
| FBG (mmol/L) | 4.93±0.35 | 4.87±0.40 | 4.93±0.45 | 0.59 |
| Male | 5.12±0.41 | 4.93±0.41 | 5.08±0.27 | 0.25 |
| Females | 4.88±0.32 | 4.83±0.39 | 4.85±0.50 | 0.79 |
| Impaired FBG, n (%) | 6 (6.1) | 1 (1.5) | 3 (8.1) | 0.24 |
| Blood lipids | ||||
| Total cholesterol (mmol/L) | 3.97±0.76a | 4.33±0.77b | 4.38±0.74b | 0.002 |
| Males | 3.67±0.57a | 4.52±0.84b | 4.54±0.88a | 0.001 |
| Females | 4.04±0.79 | 4.23±0.72 | 4.31±0.66 | 0.21 |
| LDL (mmol/L) | 2.18±0.67 | 2.32±0.80 | 2.43±0.82 | 0.17 |
| Males | 2.10±0.55a | 2.72±0.88b | 2.73±0.88 | 0.02 |
| Females | 2.20±0.70 | 2.09±0.66 | 2.28±0.76 | 0.52 |
| HDL (mmol/L) | 1.35±0.28a | 1.47±0.28b | 1.26±0.27a | 0.001 |
| Males | 1.17±0.24 | 1.32±0.22 | 1.29±0.23 | 0.09 |
| Females | 1.39±0.28a | 1.56±0.28b | 1.24±0.29a | <0.001 |
| Reduced HDL, n (%) | 37 (37.8) | 13 (19.1) | 20 (54.1) | 0.001 |
| Non-HDL cholesterol (mmol/L) | 2.62±0.72a | 2.87±0.77 | 3.12±0.85b | 0.002 |
| Males | 2.50±0.52a | 3.20±0.87b | 3.25±1.06b | 0.01 |
| Females | 2.65±0.76a | 2.67±0.63 | 3.07±0.74b | 0.04 |
| Triglycerides (mmol/L) | 1.05±0.44a | 1.20±0.48 | 1.42±0.73b | 0.001 |
| Males | 0.89±0.31 | 1.05±0.36 | 1.21±0.64 | 0.12 |
| Females | 1.09±0.46a | 1.29±0.53 | 1.52±0.75b | 0.002 |
| Raised triglycerides, n (%) | 8 (8.2) | 10 (14.7) | 11 (29.7) | 0.006 |
| Ratio TC/HDL | 3.04±0.74a | 3.05±0.76a | 3.67±1.14b | <0.001 |
| Males | 3.23±0.65 | 3.53±0.92 | 3.72±1.35 | 0.34 |
| Females | 2.99±0.76a | 2.77±0.48a | 3.65±1.06b | <0.001 |
| Ratio LDL/HDL | 1.69±0.65a | 1.66±0.74a | 2.05±0.95b | 0.03 |
| Males | 1.87±0.62 | 2.16±0.88 | 2.28±1.11 | 0.36 |
| Females | 1.64±0.65 | 1.38±0.45a | 1.94±0.87b | 0.003 |
| Ratio TG/HDL | 0.83±0.43a | 0.84±0.37a | 1.25±0.80b | <0.001 |
| Males | 0.79±0.33 | 0.82±0.33 | 1.03±0.70 | 0.27 |
| Females | 0.84±0.45a | 0.86±0.39a | 1.35±0.84b | <0.001 |
| Adolescents with at least one disordered MetS indicator, n (%) | 48 (49.0)a | 23 (33.8)a | 23 (62.2)b | 0.016 |
Data represented as mean ± SD, unless otherwise indicated. ab Different superscript letters across the rows denote pairwise significant differences between the ethnic groups using post hoc Tukey honestly significant difference test for continuous data, or using the χ2 test for categorical data (P<0.05). FBG Fasting blood glucose; HDL High-density lipoprotein; LDL Low-density lipoprotein; MetS Metabolic syndrome; TC Total cholesterol; TG Total triglycerides
Significant differences were noted among the ethnic groups in plasma lipid measurements (Table 2). TC was significantly lower in Europeans (P=0.002), predominantly due to the male subjects. LDL cholesterol was also significantly lower in European males while HDL cholesterol was higher in Chinese females (Table 2). Non-HDL cholesterol was lowest among Europeans for both genders, but this difference was significantly lower than Chinese and South Asian adolescents only in male subjects (P=0.01). TG levels were significantly higher among South Asians, especially among females. Over half (54%) of South Asian adolescents had abnormally decreased HDL levels (<1.03 mmol/L in males and <1.29 mmol/L in females, P=0.001) and 30% of South Asians had raised TG (>1.7 mmol/L, P=0.006). Furthermore, all plasma lipid ratios (TC/ HDL, LDL/HDL, TG/HDL) were significantly higher in South Asians than in Europeans and Chinese, mostly due to the female subjects (Table 2). According to the ethnic- and sex-specific IDF definition, the prevalence of metabolic syndrome (MetS) within the population was low: 4/203 (2%), with representation in each ethnicity. Significantly more South Asian adolescents (62%), compared with European (49%) and Chinese (34%) adolescents, had at least one disordered MetS indicator (P=0.016) (Table 2).
Diet and physical activity
No significant differences were noted among the ethnic groups in dietary intakes (Table 3). Similarly, there were no differences in the dietary intakes among different ethnicities analyzed by gender (data not shown). Self-reported intensity of physical activity was higher among Europeans (P=0.002) than among Chinese or South Asians and the difference was significant for both sexes (Table 3).
TABLE 3.
Dietary intakes and physical activity
| Parameter | Europeans n=98 | Chinese n=68 | South Asians n=37 | P value |
|---|---|---|---|---|
| Energy (kcal/day) | 2120±760 | 2124±1095 | 2186±628 | 0.34 |
| Protein (g/day) | 87.3±41.8 | 85.8±38.5 | 94.5±38.6 | 0.38 |
| Carbohydrate (g/day) | 287±107 | 292±133 | 304±100 | 0.42 |
| Total fibre (g/day) | 16.9±9.8 | 15.8±8.4 | 18.1±12.8 | 0.90 |
| Fat (g/day) | 64.2±30.9 | 68.4±46.8 | 62.3±27.5 | 0.96 |
| Saturated fat (g/day) | 25.8±14.3 | 23.8±15.3 | 26.5±10.5 | 0.12 |
| Monounsaturated fat (g/day) | 22.8±10.0 | 20.3±7.7 | 23.0±10.7 | 0.75 |
| Polyunsaturated fat (g/day) | 11.4±9.1 | 7.3±7.0 | 8.4±7.5 | 0.07 |
| Trans fat (g/day) | 3.4±4.9 | 4.2±4.8 | 4.4±6.5 | 0.65 |
| Cholesterol (mg/day) | 260±198 | 216±123 | 284±169 | 0.18 |
| Physical activity | 2.95±0.97a | 2.48±0.93b | 2.24±0.95b | 0.002 |
| Males | 3.47±0.83a | 2.65±0.93b | 2.80±0.63b | 0.03 |
| Females | 2.83±0.97a | 2.39±0.93b | 1.95±0.97b | 0.002 |
Data represented as mean ± SD. ab Different superscript letters across the rows denote pairwise significant differences between the ethnic groups using the non-parametric Mann-Whitney U test (P<0.05). Physical activity is reported on a five-point ordinal scale
DISCUSSION
As previously reported for adults, the results of this cross-sectional study of 203 multiethnic adolescents in the GTA confirm that the frequency of CVD risk factors differ depending on ethnic background. Specifically, South Asian adolescents have a worse CVD RF profile compared with their European and Chinese peers in the GTA. To our knowledge, this is the first population-based study in Canada which examined a multiethnic adolescent population with respect to diet, lifestyle and CVD risk assessment, and the first study comparing youths from these three specific ethnic groups. We previously found a high prevalence of CVD and MetS among South Asian adults, and the results of the current study suggest that this predisposition to a higher risk of heart disease seems to begin at a younger age (9,10). The significant majority of the South Asian adolescents in the present study (62%) had at least one abnormal MetS indicator, most commonly dyslipidemia, with over 50% having decreased HDL levels and elevated TG, resulting in approximately 30% having an increased TG/HDL ratio.
Anthropometric characteristics are different among ethnicities. Weight, BMI and waist circumference were significantly higher in European adolescents compared with Chinese, although the differences in BMI and waist circumference were due to differences between male subjects only. These findings are consistent with those of other researchers and IDF recommendations on waist circumference (22). In a study by Razak et al, adults from non-European ethnic groups displayed significantly higher levels of metabolic (FBG, glycosylated hemoglobin, TC/HDL) and clinical markers (systolic blood pressure) than Europeans at nearly every given level of BMI (23). It has been shown that South Asian and Chinese adults have the same level of cardiovascular risk as Europeans at a BMI approximately 6 kg/m2 lower than their European counterparts (24).
The present study found no significant differences in FBG among ethnic groups (4.9 mmol/L on average) or the occurrence of impaired FBG, which was lower than the 13% reported among adolescents in NHANES (25). However, recent data from our SHARE study has shown that FBG levels can be higher among South Asian adults compared with European and Chinese Canadian adults (5.5 mmol/L, 5.2 mmol/L and 5.2 mmol/L, respectively) (9,10).
Significant sex differences were noted in plasma lipid measurements, which is consistent with previous studies (21). Among the ethnic groups, TC and LDL were significantly lower in Europeans, predominantly among males, while HDL cholesterol was higher in Chinese females. Over one-half of South Asian adolescents had abnormally decreased HDL levels and 30% had raised TG, indicating the presence of dyslipidemia. Furthermore, all plasma lipid ratios (TC/HDL, LDL/HDL, TG/HDL) were significantly higher in South Asian than in European and Chinese adolescents. Similarly, in an adult population survey of 3754 middle-aged men and women in London, United Kingdom, in comparison with the European group, the South Asians had higher plasma TG and lower HDL cholesterol concentrations (13). In the SHARE study in adults, South Asians also had higher TC and LDL cholesterol, TG, apolipoprotein A, and lower HDL cholesterol (9). In contrast, a previous study by Hanlin et al of high school students did not find significant differences in lipids levels, as well as BMI, although, similar to our study, South Asians had a higher number of CVD risk factors compared with Caucasians (26).
According to the ethnic- and gender-specific IDF definition, the MetS prevalence within our population was 4/203 (2%), with representation in each ethnicity. The majority of South Asian (62%), almost half of European (49%) and a third of Chinese adolescents (34%) had at least one MetS indicator. This is fairly consistent with a recent paper by Johnson et al from NHANES, in which about half of the participants had at least one disordered measurement, with an overall MetS prevalence of 8.6%, which is higher than our data, partly due to different MetS criteria used by Johnson et al (7). Also using NHANES data, Cook et al reported that the prevalence of MetS among adolescents varied from just >9% to as low as 2%, depending on the criteria used (27). Therefore, our population is on the lower limit of this MetS estimate; however, as our study was conducted among high school students interested in nutrition and medical research, who are more fit and have a lower BMI, it is likely that this is an underestimate compared with the general adolescent population in Canada.
Although no significant differences in dietary intakes were noted among the ethnic groups, the self-reported intensity of physical activity was higher among Europeans than Chinese or South Asians, which could partly explain the lower TC and LDL levels in Europeans. Similarly, Palaniappan et al reported less physical activity among young South Asian women, who also had higher levels of apolipoprotein A, HDL, and fibrinogen than their European counterparts (28).
Considerable ethnic variations in CVD RF among adolescents highlight the need for systematic comparisons of CVD risk among ethnic groups and the potential for detailed investigations among ‘high-risk’ ethnic populations in order to contribute new insights about the etiology and pathogenesis of atherogenic CVD. In addition, ethnic differences may play an important role in the identification of MetS in adolescents, and may guide the evaluation and establishment of a screening tool for this condition.
Limitations
The first limitation of the present study is potential sample selection bias because we used a relatively small convenience sample of students interested in nutrition. However, by selecting students from a wide distribution across the GTA we have attempted to reduce this limitation. Another limitation of our study is that we used adult CVD risk criteria, recommended for those 16 years of age or older, despite the fact that some of the participants were 15 years of age (22). Also, our study was performed on a convenience sample which prevented us from performing stratified randomization (eg, by sex or pubertal maturation status). However, we performed separate analyses by sex which minimized this bias, as well as a bias related to a higher number of females versus males in the studied population. In addition, the retrospective assessment of physical activity level using an ordinal scale was rather subjective.
CONCLUSION
Similar to adult data, South Asian adolescents have comparably higher rates of cardiovascular risk factors than their European and Chinese counterparts, which could partly be attributed to the lower physical activity of South Asians. The majority of South Asians have at least one disordered MetS indicator, including an abnormally decreased HDL and elevated TG levels. Whether our findings in these selected samples of healthy adolescents can be generalized to their respective populations requires further validation. Control of obesity and encouraging greater physical activity, and particularly lifestyle modifications, would offer the best chances for prevention of CVD in this population group.
Footnotes
FINANCIAL DISCLOSURE: Funding has been generated through donation of various food industry grant supports and the St Michael’s Hospital Research Department.
CONFLICT OF INTEREST: None.
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