Factors associated with elevated blood pressure or hypertension in Afro

26 Pages·2017·0.24 MB·English

Factors associated with elevated blood
pressure or hypertension in Afro-
Caribbean youth: a cross-sectional study
TrevorS.Ferguson1, NovieO.M.Younger-Coleman1, MarshallK.Tulloch-Reid1,
NadiaR.Bennett1, AmandaE.Rousseau1, JenniferM.Knight-Madden1,
MaureenE.Samms-Vaughan2, DeannaE.Ashley3 and RainfordJ.Wilks1
1CaribbeanInstituteforHealthResearch,UniversityoftheWestIndies,Mona,Kingston,Jamaica
2DepartmentofChildHealth,UniversityoftheWestIndies,Mona,Kingston,Jamaica
3SchoolofGraduateStudiesandResearch,UniversityoftheWestIndies,Mona,Kingston,Jamaica
ABSTRACT
Background. Although several studies have identified risk factors for high blood
pressure(BP),datafromAfro-Caribbeanpopulationsarelimited.Additionally,lessis
knownabouthowputativeriskfactorsoperateinyoungadultsandhowsocialfactors
influencetheriskofhighBP.Inthisstudy,weestimatedtherelativeriskforelevatedBP
orhypertension(EBP/HTN),definedasBP≥120/80mmHg,amongyoungadultswith
putative cardiovascular disease (CVD) risk factors in Jamaica and evaluated whether
relativerisksdifferedbysex.
Methods.Datafrom898youngadults,18–20yearsold,wereanalysed.BPwasmeasured
with a mercury sphygmomanometer after participants had been seated for 5 min.
Anthropometricmeasurementswereobtained,andglucose,lipidsandinsulinmeasured
fromafastingvenousbloodsample.Dataonsocioeconomicstatus(SES)wereobtained
viaquestionnaire.CVDriskfactorstatuswasdefinedusingstandardcut-pointsorthe
upperquintileofthedistributionwherethenumbersmeetingstandardcut-pointswere
small. Relative risks were estimated using odds ratios (OR) from logistic regression
models.
Submitted3October2017 Results. Prevalence of EBP/HTN was 30% among males and 13% among females
Accepted 29January2018 (p<0.001forsexdifference).Therewasevidenceforsexinteractionintherelationship
Published13February2018
between EBP/HTN and some of risk factors (obesity and household possessions),
Correspondingauthor
therefore we report sex-specific analyses. In multivariable logistic regression models,
TrevorS.Ferguson,
factors independently associated with EBP/HTN among men were obesity (OR 8.48,
[email protected],
[email protected] 95%CI[2.64–27.2],p<0.001),andhighglucose(OR2.01,CI[1.20–3.37],p=0.008),
while high HOMA-IR did not achieve statistical significance (OR 2.08, CI [0.94–
Academiceditor
AntonioPalazón-Bru 4.58],p=0.069).Insimilarmodelsforwomen,hightriglycerides(OR1.98,CI[1.03–
3.81], p=0.040) and high HOMA-IR (OR 2.07, CI [1.03–4.12], p=0.039) were
AdditionalInformationand
Declarationscanbefoundon positivelyassociatedwithEBP/HTN.LowerSESwasalsoassociatedwithhigherodds
page17 for EBP/HTN (OR 4.63, CI [1.31–16.4], p=0.017, for moderate vs. high household
DOI10.7717/peerj.4385 possessions;OR2.61,CI[0.70–9.77],p=0.154forlowvs.highhouseholdpossessions).
AlcoholconsumptionwasassociatedwithloweroddsofEBP/HTNamongfemalesonly;
Copyright
OR0.41(CI[0.18–0.90],p=0.026)fordrinking<1timeperweekvs.neverdrinkers,
2018Fergusonetal.
and OR 0.28 (CI [0.11–0.76], p=0.012) for drinking ≥3 times per week vs. never
Distributedunder
drinkers. Physical activity was inversely associated with EBP/HTN in both males and
CreativeCommonsCC-BY4.0
females.
OPENACCESS
HowtocitethisarticleFergusonetal.(2018),FactorsassociatedwithelevatedbloodpressureorhypertensioninAfro-Caribbeanyouth:
across-sectionalstudy.PeerJ6:e4385;DOI10.7717/peerj.4385
Conclusion.FactorsassociatedwithEBP/HTNamongJamaicanyoungadultsinclude
obesity, high glucose, high triglycerides and high HOMA-IR, with some significant
differencesbysex.AmongwomenlowerSESwaspositivelyassociatedwithEBP/HTN,
whilemoderatealcoholconsumptionwasassociatedloweroddsofEBP/HTN.
SubjectsCardiology,Epidemiology,GlobalHealth,InternalMedicine,PublicHealth
Keywords Elevatedbloodpressure,Hypertension,Cardiovasculardiseaseriskfactors,Young
adults,Caribbean,Blacks,Jamaica,Socioeconomicstatus,Prehypertension
INTRODUCTION
High blood pressure (BP) is the leading risk factor for the global burden of disease,
accountingforapproximately7%ofglobaldisabilityadjustedlifeyears(Limetal.,2012).
Recent studies suggest that while the prevalence of hypertension is decreasing in high-
incomecountries,prevalenceisincreasinginlowandmiddle-incomecountries,withthe
largestincreaseseenincountriesinsub-SaharanAfrica(Millsetal.,2016;NCDRiskFactor
Collaboration,2016).TheadverseeffectofhighBP,particularlyincreasedriskofcoronary
heartdiseaseandstroke,iscontinuousandgradedthroughouttherangeofsystolicblood
pressure (SBP) and diastolic blood pressure (DBP), down to levels of 115 mmHg and
75 mmHg, respectively (Lewingtonetal.,2002). Additionally, it has been estimated that
approximately 50% of disease burden attributable to high BP occurs at levels below the
140/90mmHgcut-offpointtraditionallyusedtodefinehypertension(Poulter,Prabhakaran
&Caulfield,2015). Recently the American College of Cardiology and American Heart
Association(ACC/AHA)proposednewguidelinesfortheevaluationandmanagementof
high BP (Wheltonetal.,2017). In this guideline, normal BP is defined having SBP <120
mmHgandDBP<80mmHg;elevatedBPisdefinedasSBPof120-129mmHgandDBP
<80mmHg;andhypertensiondefinedasSBP≥130mmHgorDBP>80mmHg.However,
most of the available data on prevalence of hypertension have used the criteria from the
SeventhReportoftheJointNationalCommitteeonthePrevention,Detection,Evaluation
and Treatment of High Blood Pressure (JNC 7), where hypertension is defined as SBP
≥140mmHgorDBP≥90mmHg,andSBPof120-139mmHgorDBPof80-89isclassified
as prehypertension (Chobanianetal.,2003). Studies reporting prevalence estimates for
children or adolescents <18 years old often use criteria from The Fourth Report on the
Diagnosis,Evaluation,andTreatmentofHighBloodPressureinChildrenandAdolescents
by the National High Blood Pressure Education Program (NHBPEP) (NationalHigh
BloodPressureEducationProgramWorkingGrouponHighBloodPressureinChildrenand
Adolescents,2004).
Reportedprevalenceofhypertension,usingJNC7orNHBPEPcriteria,inadolescents
andyoungadultsvarywidely,withestimatesgenerallyrangingfromabout2%among15–34
year-olds in Italy up to 19% among young adults 24–34 years old in the USA (Battistoni
etal.,2015).However,prehypertensionappearstobecommoninadolescentsandyoung
adults,withprevalenceestimatesrangingfrom12%–45%invariousstudiesfromcountries
such as India, Uganda, United States and Jamaica (Amma,Vasudevan&Akshayakumar,
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 2/26
2015;Fergusonetal.,2011b;Kayimaetal.,2015;Kinietal.,2016;Redwine&Daniels,2012).
GiventhathighBPinchildhoodhasbeenshowntotrackintoadulthood(Baoetal.,1995;
Chen&Wang,2008),studiesofhighBPinyouthprovideessentialinformationtoinform
interventionsthatwouldreducetheadverseeffectsofhighBPoncardiovascularhealth.
The aetiology of hypertension is multi-factorial, with complex interactions between
genetic,environmental,behaviouralandsocialfactors(Lloyd-Jones&Levy,2013;Poulter,
Prabhakaran&Caulfield,2015; Victor,2015). Established risk factors for hypertension
include increasing age, higher levels of adiposity, high dietary sodium, high alcohol
consumption,familyhistoryofhypertensionandlowersocioeconomicstatus(Lloyd-Jones
&Levy,2013). Underlying mechanism include activation of the sympathetic nervous
system, disorders of the renin-angiotensin aldosterone pathways, disorders of renal
regulation of sodium balance, insulin resistance, inflammation, arterial stiffness and
foetalprogramming(Acelajado,Calhoun&Oparil,2013;Victor,2015).
Complications of hypertension vary with race/ethnicity and it is conceivable that the
mechanisms underlying both aetiology and complications could vary similarly (Jones&
Hall,2006; Lackland,2014). Additionally, less is known about how these factors operate
in young African origin populations and how social factors, particularly in a developing
countrycontext,influencetheriskofhighBP.
In Jamaica, the prevalence of hypertension (using the JNC 7 criteria) among persons
15–74 years old was estimated at 20% in 2001, and 25% in 2008 (Fergusonetal.,2011a).
The prevalence of prehypertension was 30% in 2001 and 35% in 2008, and was shown
to be associated with other cardiovascular disease (CVD) risk factors and high rates of
progression to hypertension (Fergusonetal.,2011a; Fergusonetal.,2010c; Fergusonetal.,
2008). Among 15–19 year-old youth, the prevalence of prehypertension in 2006 was
29%(Fergusonetal.,2011b).Morerecently,theModelingtheEpidemiologicalTransition
StudyreportedprevalenceofhypertensionamongurbanJamaicans25–45yearsold,with
prevalence estimates of 6.8% among men and 10% among women (Cooperetal.,2015).
ThisstudyalsofoundthattheprevalenceofCVDriskfactorswasnotalwaysconsistentwith
thatexpected,withJamaicanwomenhavinglowerdiabetesprevalencedespitehighobesity
prevalenceandSouthAfricanmenhavinghigherprevalenceofhypertensiondespitelower
adiposity(Dugasetal.,2017).Giventhehighburdenofhypertensionandprehypertension
inJamaica,studiesevaluatingtherelativecontributionofvariousriskfactorswouldprovide
necessaryinformationtodirectpublichealthinterventions.Thispaperthereforeevaluates
theassociationbetweenputativeriskfactorsandelevatedBPorhypertension(EBP/HTN),
defined as BP ≥120/80 mmHg, among Afro-Caribbean youth. Specifically, we aimed to
estimatetherelativeriskforhavingEBP/HTNamongparticipantswithputativeCVDrisk
factors, and to evaluate whether there were significant sex differences in risk factors for
EBP/HTN.
METHODS
Data sources
Weconductedacross-sectionalanalysisusingdatafromthethirdfollowupoftheJamaica
1986 Birth Cohort Study (Fergusonetal.,2010a; McCaw-Binnsetal.,2011). This study
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 3/26
is a longitudinal study of persons, born in Jamaica in September and October of 1986,
and who were a part of the Jamaica Perinatal Mortality Survey (Ashley,McCaw-Binns&
Foster-Williams,1988).Detailsonthiscohorthavebeenpreviouslypublished(Bennettet
al.,2014;McCaw-Binnsetal.,2011).Forthisanalysis,weuseddatafrom409malesand489
females,18–20yearsold,collectedinthethirdfollowupofthecohortbetweenMarch2005
andFebruary2007.ThestudywasapprovedbytheUniversityoftheWestIndies/Faculty
of Medical Sciences Ethics Committee. Participants provided written informed consent
priortomeasurementsbeingdone.
Measurements and definitions
Alldatacollectionandmeasurementsweredonebytrainedresearchnurses.Weobtained
data on demographic characteristics, general health, medical history, behavioural health
risk factors and socioeconomic status via questionnaire. Additionally, we obtained
anthropometricandBPmeasurementsandperformedvenepunctureforanalysisofblood
glucose,lipids,insulinandcreatinine.Atimedurinesamplewasobtainedformeasurement
ofurinaryalbuminexcretion.
BP was measured with a mercury sphygmomanometer after the participant had been
seated for 5 min. BP measurement followed a standardized protocol developed for the
InternationalCollaborativeStudyofHypertensioninBlacks(Atamanetal.,1996).Three
BPmeasurementsweretakenat1-minuteintervals,withthemeanofthesecondandthird
measurements being used for analysis. EBP/HTN was defined as SBP ≥120 mmHg or
DBPof≥80mmHg,correspondingtotheprehypertensionandhypertensioncategoriesof
JNC7andtheelevatedBPandhypertensioncategoriesofthe2017ACC/AHAguidelines
(Chobanianetal.,2003;Wheltonetal.,2017).Noneoftheparticipantswereonmedication
forelevatedbloodpressureatthetimeofassessment.
Weightwasmeasuredusingaportabledigitalscale,whichwascalibrateddaily.Height
wasmeasuredusingaportablestadiometer.Waistandhipcircumferenceweremeasured
using a non-stretchable nylon tape measure. Body mass index (BMI) was calculated
as weight in kilograms divided by the square of height in metres and BMI categories
definedusingtheWorldHealthOrganizationcategories:underweight(BMI<18.5kg/m2),
normal weight (BMI 18.5–24.9 kg/m2), overweight (BMI 25.0–29.9 kg/m2), obese (BMI
≥30 kg/m2) (WorldHealthOrganization, 1995). The normal weight category was used
as the reference group. Central obesitywas defined as a waist circumference≥80 cm for
womenand≥94cmformenasrecommendedforAfricanOriginpopulationsinthe2009
Consensus Criteria for the Metabolic Syndrome (Albertietal.,2009). Waist-to-hip ratio
was calculated by dividing waist circumference by hip circumference. High waist-to-hip
ratiowasdefinedusingcut-pointsrecommendedbyLean,Han&Morrison(1995)as≥0.95
formalesand≥0.80forfemales.
Venousbloodwascollectedafteranovernightfastofatleasteighthours.Sampleswere
analysed using standard laboratory protocols for measurement of fasting glucose, lipids,
fastinginsulinandserumcreatinine.WhitebloodcellcountandhighsensitivityC-reactive
protein(hsCRP)weremeasuredasmarkersofinflammation.
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 4/26
Details of laboratory procedures have been previously published (Bennettetal.,2014;
Fergusonetal.,2010a; Rockeetal.,2015; Tulloch-Reidetal.,2010). In brief, glucose was
measured using the glucose oxidase method (Alcyon, Analyzer); total cholesterol,
triglycerides,andhighdensitylipoproteincholesterol(HDL)weremeasureddirectlyusing
enzymaticmethods(AbbottSpectrumAnalyzer),whilelowdensitylipoproteincholesterol
(LDL)wascalculatedusingtheFriedewaldequation(totalcholesterol−HDL−[TG/2.18],
with all concentrations given in mmol/L). Serum creatinine was measured using Jaffe’s
reactionontheAlcyon300ChemistryAnalyser(Abbott,Chicago,IL,USA),whilefasting
insulin was measured using a chemiluminescent immunoassay (IMMULITE; Diagnostic
ProductsCorporation,LosAngeles,CA,USA);hsCRPwasmeasuredusinganIMMULITE
immunoassay (Siemens Medical Solution Diagnostics, Los Angeles, CA). Microalbumin
was measured from a timed urine specimen using a chemiluminescent immunoassay
methodusingtheIMMULITEImmunoassaySystem(Siemens,LosAngeles,CA).
Elevatedglucose(≥5.6mmol/L),elevatedtriglycerides(≥1.7mmol/L)andlowlevelsof
highdensitylipoproteincholesterol[HDL](<1.0mmol/Lformalesand<1.3mmol/Lfor
females)weredefinedusingthemetabolicsyndromecriteria(Albertietal.,2009).Hightotal
cholesterol (≥5.2 mmol/L) and high levels of low density lipoprotein [LDL] cholesterol
(≥4.1 mmol/L) were defined using the National Cholesterol Education Program Adult
TreatmentPanelIII(ATPIII)criteria(ExpertPanelonDetectionEvaluationandTreatment
ofHighBloodCholesterolinAdults,2001).Foranalysesincludingglucoseandtriglycerides
values in the upper quintile of the distribution were defined as elevated, because the
proportion of participants meeting the metabolic syndrome cut-points was very small,
thusresultingintoofewparticipantsformultivariableanalyses.HighhsCRPwasdefined
as >3.0 mg/L, with values >10 mg/L set to missing, as recommended by the American
HeartAssociationandCentersforDiseaseControl(Pearsonetal.,2003).Insulinresistance
wasestimatedusingtheHomeostasisModelAssessment(HOMA-IR)equations(Matthews
etal.,1985). Values for HOMA-IR were log transformed to account for non-normal
distribution. Elevated HOMA-IR was classified as being in the upper quintile of the
log-HOMA-IR. For this paper we chose to dichotomize these characteristics in order to
quantifytheeffectofbeinginanabnormal(highrisk)categoryandfacilitatethetailoring
of public health messages aimed at risk reduction. Urine albumin and creatinine levels
wereusedtocalculatethealbumintocreatinineratio(ACR)andelevatedurinealbumin
definedasACR≥30mg/gasrecommendedbythe2012KidneyDiseaseImprovingGlobal
Outcomes (KDIGO) Guidelines (KidneyDisease:ImprovingGlobalOutcomes(KDIGO)
CKDWorkGroup,2013).
Socioeconomic status was assessed using data collected using a locally developed
questionnaire on parental education and occupation, and number of household
possessions. The specific questionnaire items are included in the supplementary files
availableonline.Dataoneducationwascollectedasthehighestlevelofeducationattained
by either parent or guardian and then categorized as: post-secondary, secondary, or less
than secondary. In Jamaica, children are required to complete a mandatory six years of
elementary school (Grades 1–6) and five years of high school (Grades 7–11 or first to
fifth form), after which they graduate from high school. Children may spend an extra
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 5/26
two years in sixth form (Grades 12 and 13) before going on to university or college. In
this classification, post-secondary education includes persons who completed college or
university and persons with vocational training obtained after completing high school.
Secondaryeducationindicatespersonswhocompletedhighschool(uptograde11)and
lessthansecondaryincludespersonswhodidnotcompletehighschool(i.e.,highschool
education up to grade 10 or below). Occupational categories were defined using the
occupation of the household head and coded using the Jamaica Standard Occupational
Classification (JSOC) (StatisticalInstituteofJamaica,1995). For this report occupation
categories were classified as professionals or managers, office, service or trade workers,
andsemi-skilledorunskilledworkers.Forhouseholdpossessions,participantswereasked
toindicatewhethertheyhaditemsfromalistof17householdpossessionsandgivenone
point for each item. They were then classified in three possession score categories based
on the distribution of items: low (0–9 items), moderate (10–14 items), and high (15–17
items). The list of items included in the possession score is shown Table S1. Cut-points
for this classification was chosen based on the finding that the majority of participants
had10–14items,sothatthegroupswith0–9itemswouldrepresentthelowerendofthe
distributionand15–17itemstheupperendofthedistribution.
Dataonphysicalactivity,smoking(cigarettesormarijuana)andalcoholconsumption
werealsocollectedviaquestionnaire.Forsmoking,participantswereclassifiedascurrent
smokers or non-smokers, while for alcohol consumption participants were classified as:
‘neverdrankalcohol’,‘rarelydrinksalcohol’(<1timeperweek),‘drinksalcohol1–2times
per week’, or ‘drinks alcohol ≥3 times per week’. Physical activity was classified based
on the time spent doing sports or exercise during leisure time using a locally developed
questionnaire.Questionnaireitemsincludedquestionsontimespentdoingactivesports
orotheractivitiessuchasbriskwalking,jogging,liftingweights,danceclasses,andworkout
atagym.Thespecificquestionnaireitemsareincludedintheonlinesupplementaryfiles.
Physicalactivityassessedusingthisquestionnairewasshowntobemorestronglyassociated
with measures of obesity than the International Physical Activity Questionnaire (IPAQ)
(Youngeretal.,2007).Participantswithnoleisuretimephysicalactivitywereclassifiedas
low physical activity level, those with <3.5 h per week as moderate physical activity level
andthosewith3.5hormoreperweekashighphysicalactivitylevel.
Sample size and power
Giventhatwehadafixedavailablesamplesizeof409malesand489femalesandthatwe
performedsex-specificanalyses,weestimatedthemaximumdetectableoddsratioinstead
ofsamplesize.Theseestimateswerecomputedformalesandfemales,separately,usingthe
power twoproportions command available in Stata 14 (StataCorp, 2015c). We estimated
theprevalenceoftheoutcomevariable(EBP/HTN),fromthesampleat30%formalesand
13%forfemales,andusedtheseandtheavailablesamplesizetocomputethemaximum
detectableoddsratioforexposures,withproportionexposedrangingfrom0.1to0.5for
power of 80% at the 5% significance level. For males, the given sample size of 409 had
80%powertodetectoddsratioof1.84iftheproportionexposedwas0.5and2.13ifthe
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 6/26
proportion exposed was 0.2. For females the given sample size of 489 had 80% power
to detect odds ratio of 2.02 if the proportion exposed was 0.5 and 2.34 if the proportion
exposedwas0.2.
Statistical methods
WeperformeddataanalysiswithStataversion14.1software(StataCorp.,CollegeStation,
TX, USA). We obtained descriptive statistics (means and proportions) for outcome and
explanatory variables within and across sex and blood pressure categories. If data were
highly skewed, we reported the median and interquartile range instead of the mean and
standard deviation. Proportions were compared using the Pearson’s chi-squared test
or Fisher’s exact tests, as appropriate. Differences in means were compared using the
unequal variance two sample t-test. Differences in medians were compared using the
non-parametricequalityofmediantestavailableinStata(StataCorp,2015a).
Logistic regression and two-way analysis of variance (ANOVA) models were used to
determine if there was evidence for sex interaction in the relationship between BP and
some of the explanatory variables. Results for analyses assessing interaction using the
logisticregressionmodelsareshowninTableS2.Therewasevidenceforsexinteractionin
therelationshipbetweenEBP/HTNandsomeofriskfactors(obesity,centralobesityand
householdpossessions),thereforewereportsex-specificresultsforregressionanalyses.
Weusedmultipleimputationbychainedequationstoaccountformissingdataforsome
explanatoryvariables.Theproportionofcompletecases,i.e.,participantswithnomissing
valuesforanyofthevariablesofinterest,was43%(n=384);Themajorityofincomplete
cases(30%ofparticipants)hadonlyhadonemissingvalue;14%hadtwomissingvalues,
7% had three missing values and 7% had more than three missing values. Details on
the number of missing values for each variable are shown in Table S3. A comparison of
thecompletecasesvs.theincompletecasesrevealedonlyminordifferences.Participants
with missing values were more likely to have albuminuria, fewer household possessions,
lowerphysicalactivityandloweralcoholconsumption,buthadnostatisticallysignificant
differencesforanyothercharacteristics.Giventheproportionofparticipantswithatleast
one missing value and the observed differences between complete and incomplete cases,
multipleimputationwasusedtoimprovethepowerofthestudyandreducebiasthatmay
beseeninthecompletecaseanalysis(Nguyen,Carlin&Lee,2017;White,Royston&Wood,
2011).Astackedmultipleimputeddataset,consistingoftheoriginaldatasetand25data
setswithimputationsformissingvalues,wascreatedusingStata’smisuiteofcommands
(StataCorp,2015b).Wecomparedimputedvariablevaluestotheobservedvaluestoensure
thattheimputedvalueswereplausible;thesedataareshowninTableS4.
Bivariate logistic regression was used to assess the association between EBP/HTN and
individual explanatory variables. These bivariate models were estimated using Stata’s mi
suiteofcommandsandestimatescombinedbythesoftwareusingRubinrules(Marshall
etal.,2009;StataCorp,2015b).Foruseinmodelselection,weextractedthefirstofthe25
imputeddatasetsandperformedregularbinarylogisticregressiononthesingle-imputed
data,asrecommendedbyWood,WhiteandRoyston(Wood,White&Royston,2008).We
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 7/26
used the backwards stepwise regression algorithm available in Stata to identify variables
for inclusion in the final model. All variables hypothesized to be associated with the
outcome were included in the first multivariable model and p-value > 0.2 was used to
removevariablesfromthemodel.WethenusedthePearsonandHosmer-Lemeshowtests
for goodness-of-fit to assess the models. Finally, we used Akaike information criterion
(AIC)todeterminewhethertoincludeorexcludespecificvariablesfromthefinalmodels.
Final multivariable models were then run on the multiple imputed data set with 25
imputations,usingStata’smisuiteofcommandsandestimatescombinedbythesoftware
usingRubinrules(Marshalletal.,2009;StataCorp,2015b).Toassessthepotentialimpact
of the imputed values on the final conclusions we also re-ran the final models without
imputations(i.e.,completecaseanalysis);theseresultsareshowninTableS5.
RESULTS
SummarystatisticsfordemographicandbiomedicalmeasurementsareshowninTable1.
Mean age at the time of the study was 18.8 years (SD = 0.61), with no sex difference.
Comparedtofemales,maleshadhighermeanweight,height,SBP,DBP,fastingglucose,
triglycerides and creatinine, while females had higher mean total cholesterol, LDL and
HDL cholesterol. Females also had higher median hsCRP, fasting insulin concentration
andHOMA-IR.Comparisonsofparticipants’characteristicsbyBPcategoriesareshownin
TableS6.Overall,participantswithEBP/HTNtendedtohavehighermeanvaluesofCVD
riskfactors.
Proportions of participants with EBP/HTN and other CVD risk factors, expressed as
categoricalvariables,areshownisTable2.OverallprevalenceofEBP/HTNwas21%and
wastwiceashighinmencomparedtowomen(30%vs.13%,p<0.001).Theprevalenceof
elevatedBP(SBP120–129mmHg,DBP<80mmHg)was9%(13%amongmalesand5%
amongfemales,p<0.001),whilehypertension(BP≥130/80mmHg)prevalencewas12%
(17%amongmalesand8%amongfemales,p<0.001).Prevalenceofobesitywas8%(6%
amongmalesand10%amongfemales,p=0.008).Themajorityofparticipantswerefrom
middle-income households, with the household head having completed secondary level
educationandworkingasoffice,service,ortradeworkers.Lowphysicalactivitylevelwas
reportedby34%ofparticipantsandhighphysicalactivityby24%.Thereweresignificant
sex differences in physical activity among males compared to females (p<0.001) with
47%offemalesreportinglowphysicalactivitylevelscomparedto18%amongmales,while
high physical activity was reported by 38% of males compared to 13% among females.
Cigarette smoking was reported by 14% of males and 6% of females (p<0.001), while
31% of males and 7% of females smoked marijuana (p<0.001). Males also reported
higherlevelsofmoderate(≥3times/week)alcoholconsumption(38%vs.19%,p<0.001).
SimilaranalysesstratifiedbyBPcategoryareshowninTableS7.Significantdifferenceby
blood pressure category were seen for BMI categories, central obesity and waist-to-hip
ratioamongmales,andfornumberofhouseholdpossessionsamongfemales.
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 8/26
Table1 Meanormedianvaluesforparticipantcharacteristicsandputativehypertensionriskfactors
formales,femalesandbothsexes.
Characteristic Male Female Bothsexes
n=409 n=489 N =898
Mean±SD Mean±SD Mean±SD
Age(years) 18.8±0.59 18.8±0.62 18.8±0.61
Weight(kg)*** 71.1±14.2 62.4±15.5 66.4±15.5
Height(cm)*** 176.8±6.5 163.6±6.1 169.6±9.1
Bodymassindex(kg/m2) 22.7±4.3 23.3±5.6 23.0±5.0
Systolicbloodpressure(mmHg)*** 113.9±10.4 107.4±8.8 110.3±10.1
Diastolicbloodpressure(mmHg)*** 69.2±10.3 66.9±9.2 67.9±9.8
Waistcircumference(cm) 75.2±10.8 73.9±12.1 74.5±11.5
Hipcircumference(cm)** 94.4±8.9 96.5±11.0 95.5±10.2
Waist-to-Hipratio*** 0.80±0.08 0.77±0.14 0.78±0.12
Whitebloodcellcount(cells×109/L)*** 5.3±1.6 6.4±2.0 5.9±1.9
Fastingglucose(mmol/L)*** 4.7±0.6 4.4±0.4 4.6±0.5
Totalcholesterol(mmol/L)*** 4.1±0.8 4.5±0.9 4.3±0.9
HDLcholesterol(mmol/L)*** 1.1±0.2 1.2±0.3 1.2(0.3)
LDLcholesterol(mmol/L)*** 2.7±0.7 3.0±0.8 2.9±0.8
Triglycerides(mmol/L)* 0.60±0.26 0.56±0.26 0.58±0.26
Creatinine(µmol/L)*** 80.5±16.0 56.9±25.5 67.7±24.7
Median(IQR) Median(IQR) Median(IQR)
Urinaryalbumin(mg/g)* 3.9(2.5,7.4) 4.9(2.5,10.7) 4.1(2.5,9.2)
hsCRP(mg/L)*** 0.5(0.3,1.3) 0.9(0.3,2.3) 0.7(0.3,1.8)
Fastinginsulin(pmol/L)*** 4.4(2.7,7.1) 6.8(4.1,10.1) 5.8(3.3,8.8)
HOMA-IR*** 0.6(0.3,0.9) 0.9(0.5,1.3) 0.7(0.4,1.1)
Notes.
*p<0.05.
**p<0.01.
***p<0.001.
SD, standarddeviation; HDL, highdensitylipoprotein; LDL, lowdensitylipoprotein; IQR, interquartilerange(values
correspondtothe25thand75thcentiles); hsCRP, highsensitivityC-reactiveprotein; HOMA-IR, HomeostasisModel
Assessment—InsulinResistance.
Differencesinmeanswerecomparedusingthetwo-samplettestwithunequalvariances,whilethedifferencesinmedianswere
computedusingthenonparametricequality-of-medianstest.
Theresultsfrombivariateanalysesyieldingsexspecificoddsratiosfortherelationship
between correlates and putative risk factors for EBP/HTN are shown in Table 3. Factors
associated with EBP/HTN among males in bivariate analyses were: age, obesity, central
obesity,highglucose,hightriglyceridesandhighHOMA-IR.Amongfemales,significant
correlateswereage,height,hightriglycerides,highHOMA-IRandnumberofhousehold
possessions. There were no significant associations for general or central obesity among
females,andnosignificantassociationsformeasuresofinflammation(hsCRPandwhite
bloodcellcount)orurinealbuminexcretionineithersex.
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 9/26
Table2 ProportionofparticipantsincategoriesforbloodpressureandotherCVDriskfactorsfor
males,femalesandbothsexes.
Characteristic Male Female Bothsexes
n=409 n=489 N =898
%(n) %(n) %(n)
ElevatedBPorhypertension(BP≥120/80mmHg)*** 29.8(122) 13.4(66) 20.9(188)
ElevatedBP(SBP120–129&DBP<80mmHg)*** 13.2(54) 5.3(26) 8.9(80)
Hypertension(BP≥130/80)*** 16.6(68) 8.2(40) 12.0(108)
Stage1hypertension(BP130–139/80–89)*** 14.7(60) 7.4(36) 10.7(96)
Stage2hypertension(BP≥140/90) 2.0(8) 0.8(4) 1.3(12)
Albuminuria 5.1(20) 8.3(39) 6.8(59)
Bodymassindexcategories***
Underweight (<18.5kg/m2) 6.1(25) 14.5(71) 10.7(96)
Normalweight (18.5–24.9kg/m2) 76.3(308) 55.2(270) 64.4(578)
Overweight (25–29.9kg/m2) 13.0(53) 19.8(87) 16.7(150)
Obese(≥30kg/m2) 5.6(23) 10.4(51) 8.2(74)
Centralobesitya,*** 5.1(21) 24.4(119) 15.6(140)
Highwaist-to-hipratiob,*** 1.0(4) 20.3(99) 11.5(103)
HighestEducationofParent/Guardianc
Post-secondary 26.2(89) 29.8(131) 28.2(220)
Secondary 61.8(210) 55.4(243) 58.2(453)
Lessthansecondary 12.1(41) 14.8(65) 13.6(106)
Occupationofhouseholdhead
Professionals/Managers 23.5(88) 24.7(114) 24.1(202)
Office,serviceortradeworkers 49.3(185) 50.9(235) 50.2(420)
Semi-skilled/Unskilledworkers 27.2(102) 24.5(113) 25.7(215)
Numberofhouseholdpossession
High(15–17items) 16.9(69) 13.7(67) 15.2(136)
Moderate(10–14items) 56.9(232) 54.2(265) 55.4(497)
Low(0–9items) 26.2(107) 32.1(157) 29.4(264)
Physicalactivitylevel***
High 37.5(153) 13.1(64) 24.2(217)
Moderate 44.4(181) 39.5(193) 41.7(374)
Low 18.1(74) 47.4(232) 34.1(306)
Currentcigarettesmoking*** 13.7(56) 6.1(30) 9.6(86)
Currentmarijuanasmoking*** 31.3(127) 7.2(35) 18.1(162)
Alcoholconsumption***
Neverdrankalcohol 6.4(26) 13.2(64) 10.1(90)
Rarelydrinksalcohol 26.4(107) 45.2(219) 36.6(326)
Drinksalcohol1–2times/week 29.1(118) 22.3(108) 25.4(226)
Drinksalcohol ≥3times/week 38.0(154) 19.4(94) 27.9(248)
Notes.
*p<0.05.
**p<0.01.
***p<0.001.
BP, bloodpressure; SBP, systolicbloodpressure; DBP, diastolicbloodpressure; CVD, cardiovasculardisease.
aCentralobesitydefinedaswaistcircumference≥94cminmalesand≥80cminfemales.
bHighwaist-to-hipratio≥0.95formalesand≥0.80forfemales.
cEducationcategory‘‘post-secondary’’includespersonswithvocationaltraining,college,oruniversityeducation;secondary
correspondstohighschool(uptograde11);lessthansecondarycorrespondstopersonswhohadonlyelementaryschooledu-
cationorpersonswhodidnotcompletehighschool(i.e.,highschoolgrade10orbelow).
Fergusonetal. (2018),PeerJ,DOI10.7717/peerj.4385 10/26