Cardiovascular Risk in Xavante Indigenous Population

Introduction

Cardiovascular diseases (CVDs) are the main cause of mortality and morbidity inBrazil and the world. Approximately one third of deaths are caused by CVDs. Besides,they constitute one of the main causes of long hospital stay and health costs inBrazil.^1,2

Most CVDs result from unhealthy lifestyle and modifiable risk factors. Altered lipidprofile, diabetes mellitus, smoking, advanced age, family history, sedentarylifestyle and weight excess are the main predisposing factors for CVDs.^1-3 CVDs start in early stages of lifeand progress silently until first manifestations in advanced stages. The earlier therisk factors are identified, the higher the possibility of prevention to prevent andreduce complications.²

The prevalence of cardiovascular risk factors is still poorly investigated inindigenous populations in Brazil. In the last decades, considerable changes ineating habits and physical activity level have occurred in Xavante people,contributing to increased prevalence of non-communicable chronic diseases in thispopulation.^4,5 However, despite significant literature on health conditions,there are no studies on cardiovascular risk in this indigenous group.

Considering that CVDs increase the risk of premature deaths, disabilities anddecreased quality of life, and exert an economic impact for families, communitiesand society, determining the prevalence of cardiovascular risk factors would bevaluable for the establishment of prevention strategies.²

The aim of this study was to evaluate the prevalence of cardiovascular risk factorsin Xavante adults from São Marcos and Sangradouro/Volta Grande indigenousreserves in Mato Grosso state, Brazil.

Methods

This was a cross-sectional study of Xavante adults living in São Marcos andSangradouro/Volta Grande indigenous reserves in Mato Grosso State, Brazil.

The study was approved by the Research Ethics Committee of Hospital dasClínicas da Faculdade de Medicina de Ribeirão Preto - USP, EscolaPaulista de Medicina - UNIFESP, CONEP and FUNAI.

Xavante communities live in eight indigenous reserves located in Mato Grosso State,Brazil. The study was conducted by periodic visits made to these communities fromOctober 2008 to January 2012. Total population of indigenous in these reserves isestimated to be 4,020 people, 1,582 of them aged 20 years or older.⁶ All subjects aged 20 years or olderwere invited to participate in the study.

Physical examination, including anthropometry, and collection of blood samples wereperformed in the villages. After being informed about the study objectives, thetribe chiefs and participants gave their consent, mostly written. To illiterateparticipants (14%), the consent forms were read by community health agents, andfingerprints were used to confirm their agreement to participate in the study.

The following variables were assessed: sex, age, weight (Kg), height (m), waistcircumference (WC) (cm), triglyceride levels (TG) (mg/dL), total cholesterol (TC)(mg/dL), low-density lipoprotein cholesterol (LDL-c), high-density lipoproteincholesterol (HDL-c), apolipoproteins A1 and B (apo 1 and apo B) (mg/dL), capillaryblood glucose levels at baseline and at 2 hours (mg/dL), systolic and diastolicarterial pressure (mm/Hg), high-sensitivity C-reactive protein (hs-CRP) (mg/dL).

Body weight was measured using an electronic scale (Plenna®), with maximumcapacity of 150 Kg, and height was measured using a portable stadiometer(Alturexata®). Weight and height values were used for body mass index (BMI)calculation (weight (kg)/height(m)²].⁷ WC was measured using an inelastic measuring tape at themidpoint between the lowest rib and iliac crest, at standing position.

Venous blood was collected after an 8-10 hour fast, using sterile disposable tubes(Vacutainer ®). Samples were stored at -20ºC and transported to a laboratoryin Sao Paulo, Brazil. Measurements of serum TG, TC, LDL-c, HDL-c, apo A1 and apo Bwere determined by enzymatic methods, and hs-CRP levels were determined byimmunoturbidimetry.

Blood pressure (BP) was measured on the left arm in the sitting position after 5minutes at rest, using an automatic digital monitor (OMRON HEM-742INTC®).Measurements were taken three times, and the mean of the last two measurements wasconsidered for analysis.

Capillary blood glucose at baseline and two hours after a 75 g anhydrous glucoseoverload (Glutol®) were measured using a portable glucose meter(HemoCue® Glucose 201, HemoCue AB).

Castelli index I (TC/HD/l-c ratio) and II (LDL-c/HDL-c ratio)⁸, TG/HDL-c,⁹ ApoB/ApoA1¹⁰ and Framingham risk score¹¹ were calculated. Hypertriglyceridemic waist (HW)was defined as the simultaneous presence of increased WC and increased TGlevels.¹²

Indicators of cardiovascular risk used in the study are described in Chart 1.^7-17

Results

Study population was composed of 925 Xavante people, 455 (49.2%) men and 470 (50.8%)women. Most (57.0%) of them were aged between 20 and 39 years.

Cardiovascular risk indicators are presented as mean and standard deviations in Table 1. Mean apo A1, WC, BMI and glucoselevels were higher in women than men, whereas mean Castelli index I and II,Framingham score, Apo B/Apo A-I ratio and systolic and diastolic BP were higher inmen than in women.

We found a high prevalence of elevated cardiovascular risk according to HDL-c, TG,TG/HDL-c ratio, CRP-hs, BMI, WC, HW and glucose levels, although a small number ofparticipants had increased levels of TC or LDL-c. In general, participants agedbetween 40 and 59 years were the most exposed to cardiovascular risk factors (Tables 2 and 3).

Discussion

Our findings show that Xavante people have an increased risk for CVDs according toHDL-c, TG, TG/HDL-c ratio, CRP-hs, BMI, WC, HW and glucose levels. Based on this,the prevalence of these diseases and consequently the risk of death, disabilities,and reduced quality of life may increase in this population in the next years.

Although several methods and indicators may be used to estimate cardiovascular risk,none of them can predict cardiovascular risk alone, and hence, should be evaluatedtogether.

One of the cardiovascular risk factors evaluated in our study was lipid profile. Therisk for atherosclerotic disease is associated with increased TC and LDL-c levelsand low HDL-c levels.¹³ Withrespect to TG, however, there is no consensus on whether they are a direct cause ofatherosclerosis or a marker of other high-risk conditions.¹⁸ Only a small percentage of Xavante people hadincreased TC and LDL-c levels. Nevertheless, similarly to other indigenouspopulations,^19,20 the Xavantes showed a high prevalence of increased TG anddecreased HDL-c levels.

Castelli index I (CT/HDL-c) and II (LDL-c/HDL-c) and the TG/HDL-c ratio have beenused to assess the combined influence of cardiovascular risk factors.^8,9 We did not find an increasedcardiovascular risk according to these indexes in the study population; however,values of TG/HDL-c ratio in 49.1% of women and 60.0% of men were indicative of highcardiovascular risk, corroborating the increased levels of TG and decreased levelsof HDL-c observed in the population.

Plasma apolipoproteins A1 and B and the apo B/apo A1 ratio have been described as thebest predictors of cardiovascular risk as compared with lipid and lipoprotein levelsor the Castelli index I and II.^21,22Apolipoproteins are structural and functional components of lipoproteins. Apo A1constitutes non-atherogenic lipid fractions (HDL-c), whereas apo B constitutesatherogenic ones (chylomicrons, LDL, IDL and VLDL). Thus, apo B/apo A1 ratiorepresents the balance between atherogenic and antiatherogeniclipoproteins.^21,22Increased apo B and apoB/A1 and reduced apo A1 levels have been consistentlyassociated with risk for CVDs.²²In our study group, 12.2% of women and 9.3% of men had an apo B/apo A1 ratioindicative of cardiovascular risk. We have not found any studies evaluating theseindicators in other indigenous populations.

CRP, an acute-phase protein released into blood in response to inflammatory cytokinesand a biomarker of systemic inflammation, was also evaluated in the current study.Increased CRP levels have been associated with coronary disease and stroke, even inpatients with normal lipid profile.¹⁴ Approximately half of Xavante people had CRP-hs levelsindicative of high cardiovascular risk. However, caution is needed in interpretingthese data, as other inflammatory diseases can also increase CRP levels. Infectiousand parasite diseases are common in indigenous populations, including the Xavantepeople, which may have influenced the results.

Framingham score is one of the algorithms used in detecting the risk forCVDs.¹¹ In our study,15.2% of men and 5.7% of women have increased risk of developing CVDs in the next 10years according to this score. Although this score has been developed for subjectsaged 30 years or older, in the current study, patients aged between 20 and 29 yearswere also included, corresponding to 28.0% of the study population. In the "age"component of Framingham score calculation, these subjects received the ratingassigned for individuals aged between 30 and 34 years (zero). No participant agedbetween 20 and 39 years showed increased cardiovascular risk. Despite its highpredictive value, Framingham score does not consider weight excess or sedentarylifestyle, both considered important cardiovascular risks.²³

Studies have reported a considerable increase in the prevalence of overweight andobesity in indigenous populations.^4,5,24Studies conducted in specific populations have shown a high proportion of overweightand obese adults, greater than 50% in some age groups.^25-27

Obesity is an important risk factor for CVDs. It is independently associated withrisk for coronary disease, atrial fibrillation and heart failure. On the other hand,obesity, particularly abdominal or visceral obesity, is associated with otherfactors known to increase cardiovascular risk, such as systemic arterialhypertension (SAH), diabetes mellitus, hypertriglyceridemia and low HDL-c.²³

More recently, HW has also been used as an indicator of cardiometabolic risk. HW isdefined as the simultaneous presence of increased WC and increased TG levels, andmay be used in the screening of patients likely to have the atherogenic metabolictriad - fasting hyperinsulinemia; hyperapolipoprotein B; and high proportion ofsmall, dense LDL-c. For this reason, HW has been used as a practical, viable,low-cost tool in the identification of patients with high cardiovascularrisk.^12,28 The prevalence of HW found in our study group (50.6% in womenand 38.0% in men) was higher than that reported in other Brazilianstudies.^29,30

Diabetic subjects have from twice to three times the risk to suffer a cardiovascularevent.³¹ Besides,cardiovascular and cerebrovascular diseases are important causes of death indiabetes mellitus patients, accounting for up to 80% of deaths.^32,33

Altered glucose levels is a health problem of large magnitude in Xavante people. Inthe present study, 70.2% of women and 46.8% of men had diabetes and decreasedglucose tolerance, indicating that they constitute a vulnerable group. This was amuch higher prevalence as compared with that in the Brazilian population.³⁴

SAH is also an important risk factor for CVDs.¹⁷ The prevalence of SAH in Xavante people - 14.7% in womenand 18.0% in men - was lower than mean values reported in Brazilian adultpopulations, ranging from 20.0%³⁵to 24.1%.³⁶

As compared with the Xavantes of Pimentel Barbosa reserve, there was a tendency ofincrease in the prevalence of SAH. In 1962, no cases of HAS was observed in thispopulation.³⁷ In 2009,however, the prevalence reached 8.1% among men and 5.8% among women.³⁸ This may result from social,cultural, economic and environmental changes in Xavante people, that culminated inreduction of physical activity and changes in eating habits with increasedconsumption of packaged foods high in sugar, fat and sodium.^4,27

This study has some limitations. Despite the large sample size, it corresponded toonly 60% of the total estimated subjects aged 20 years or older in thesecommunities, suggesting a selection bias, since healthier individuals tend to beless interested in participating in the study. In addition, some smaller, lessaccessible indigenous communities were not included in the study, affecting theparticipation rate. Limitations regarding communication between indigenous peopleand investigators, which may have been a source of bias, were partly prevented byparticipation of health professionals, members of the indigenous community in datacollection. Also, due to cultural differences, we cannot assure that all volunteerswere in fasting conditions on blood collection day despite instructions to do so; inaddition to a more irregular eating pattern, they may have not understood theimportance of such condition for laboratory tests. Thus, caution is need ininterpreting TG levels and TG/HDL ratio and HW values. Another limitation was thefact that we did not evaluate smoking habit, which is a key cardiovascular riskfactor, not only isolated but also as a Framingham score component. All subjectswere rated as non-smokers in the score calculation, and hence the possibility thatcardiovascular risk by this indicator was underestimated cannot be ruled out.

These results are significant for this population and, to our knowledge, this is thefirst study to evaluate cardiovascular risk using all these indicators.

Conclusions

Xavante people have high cardiovascular risk according to indicators such as HDL-c,TG/HDL-c ratio, BMI, WC, HW and glucose levels.

Considering that CVD patients are initially asymptomatic, and that CVDs are importantcauses of morbidity and mortality, the present analysis of cardiovascular riskfactors may be used as a basis for the planning of preventive measures and earlytreatment to minimize the impact of these diseases on this population.