Annals of African Medicine

ORIGINAL ARTICLE
Year
: 2014  |  Volume : 13  |  Issue : 4  |  Page : 151--156

Body mass index as a determinant of carotid intima-media thickness in Nigerian adults with primary hypertension


O Umeh Eric, M Agunloye Atinuke, O Adeyinka Abiodun, J Adekanmi Ademola 
 Department of Radiology, University College Hospital, Ibadan, Oyo State, Nigeria

Correspondence Address:
M Agunloye Atinuke
Department of Radiology, University College Hospital, Ibadan, Oyo State - 23402
Nigeria

Abstract

Background: Long standing hypertension may result in thickening of arterial walls and is reportedly strongly correlated with body mass index (BMI). B-mode ultrasound is a reproducible method for evaluating adaptive vascular changes. The aim of this study is to determine the relationship between body mass index and ultrasound measured carotid intima-media thickness (CIMT) among adults with primary hypertension. Materials and Methods: One hundred and twenty adults of both genders diagnosed with primary hypertension at the University College Hospital (UCH), Ibadan underwent B-mode ultrasound evaluation of the walls of the common and extracranial internal carotid arteries bilaterally. Participants«SQ» height and weight were measured and body mass index (BMI) was calculated. Results: Study population had gender distribution of 50 (41.7%) and 70 (58.3%) for males and females, respectively; and a mean age of 50.61 ΁ 10.94 years. Mean height, weight, and BMI were 1.66 m, 69.36 kg, and 24.92 kg/m 2 for male subjects and 1.59 m, 65.6 kg, and 25.6 kg/m 2 for female subjects, respectively. Normal/underweight and overweight/obese male participants had mean CIMT of 0.744 and 0.820 mm (P < 0.05) on the right side of the neck and 0.740 and 0.816 mm (P < 0.05) on the left side, respectively. However, female participants showed no statistically significant variation in CIMT values for both BMI groups. Conclusion: B-mode ultrasound demonstrates statistically significant variation in CIMT values between normal/underweight and overweight/obese male adults diagnosed with primary hypertension.



How to cite this article:
Eric O U, Atinuke M A, Abiodun O A, Ademola J A. Body mass index as a determinant of carotid intima-media thickness in Nigerian adults with primary hypertension.Ann Afr Med 2014;13:151-156


How to cite this URL:
Eric O U, Atinuke M A, Abiodun O A, Ademola J A. Body mass index as a determinant of carotid intima-media thickness in Nigerian adults with primary hypertension. Ann Afr Med [serial online] 2014 [cited 2019 Oct 20 ];13:151-156
Available from: http://www.annalsafrmed.org/text.asp?2014/13/4/151/142274


Full Text

 Introduction



Hypertension in adults may be defined as a resting systolic blood pressure of 140 mmHg or greater, and/or a diastolic blood pressure of 90 mmHg or greater. [1],[2]

The prevalence of hypertension in adults worldwide using the old cut off measurement of 160/95 mmHg in 1984 was estimated at

10-16%. [3] In 1972, Akinkugbe [4] put the prevalence of hypertension in the adult African population at 10-15%. However, with the present adoption of 140/90 mmHg as the cut off, the prevalence is possibly much higher. A survey by the 1997 expert committee on noncommunicable diseases in Nigeria put the prevalence of hypertension in adult Nigerians aged 15 years and above, to be 17-20%. [5] More recently, Ogah et al., [6] reviewed previous studies on hypertension in Nigeria and reported an overall prevalence ranging from 8-46.4% depending on the study target population, type of measurement, and cut off value used for defining hypertension. Hypertension is classified as either primary (essential) or secondary. [7] Heredity is the most important known factor in the development of essential hypertension. [8] However, primary hypertension is also strongly associated with lifestyle including such habits as smoking and alcohol consumption. It is responsible for the vast majority of diagnosed cases of hypertension and is treated with stress management, changes in diet, increased physical activity, and medication. [7]

Long standing hypertension is characterized by adaptive vascular changes, resulting in thickening of arterial walls. It is also a risk factor for the development of atherosclerosis by various mechanisms, which primarily affects the elastic arteries, as well as medium and large sized muscular arteries. [9] Hypertension is reportedly strongly correlated with body mass index (BMI). BMI is calculated from "weight (kg) divided by the square of height in meters (m 2 )". [10] Also, obesity (BMI ≥ 30 kg/m 2 ) has been documented as a good predictor of the incidence of hypertension, and is regarded as a major controllable contributor to the disorder. [11] According to Puepet et al., [10] the prevalence of obesity among adults in Jos, Nigeria is 19.4-21.4% and 23.4% for males and females, respectively. These figures may appear similar to the reported adult prevalence of obesity in the United Kingdom (23%), but are at variance with the reported prevalence of the disorder for adults in some other countries in the Organization of Economic Corporation and Development (OECD), such as the United States (34%), Mexico (30%), Korea (4%) and Japan (4%) (OECD Report 2011). [12]

B-mode ultrasound is a reproducible method to evaluate and characterize adaptive vascular changes such as arterial wall thickening and atherosclerotic progression. It permits accurate quantification of the intima-media thickness (IMT), which is a measurement of the thickness of the artery walls. Carotid IMT (CIMT) has been shown to correlate with cardiac risk factors and it is also an independent predictor of the future risk for myocardial infarction and stroke. [9],[13]

The adoption of CIMT measurements is recommended in high risk patients such as overweight or obese individuals, to help determine the likelihood of end organ damage due to hypertension, which may not be revealed by other examinations such as the electrocardiogram (ECG). [14] CIMT measurement may help clinicians to more effectively identify the vulnerable patient who will benefit from aggressive preventive intervention.

This study aims to determine the relationship if any, between weight, body mass index (BMI), and the ultrasound measured CIMT values among Nigerian adults with primary hypertension.

 Materials and Methods



This study was conducted in the Department of Radiology of our hospital between January and May 2011. Sample size was determined using the "difference of means" formula.

A total of 120 adults diagnosed with primary hypertension were recruited into the study from the hypertension clinic of the hospital using the convenience sampling method. Ethical approval for this study was obtained from the joint university and hospital ethical committee and written informed consent was obtained from all participants.

Consenting subjects aged 18 years and above were included in the study. Participants must have been diagnosed with primary hypertension at least 3 months before recruitment into this study. However, hypertensive persons less than 18 years of age, and individuals with known history or symptomatology of diabetes mellitus were excluded. Also excluded were females with pregnancy induced hypertension in which the hypertensive status was deemed transient, as well as those with previous diagnosis of peripheral artery disease, or such symptoms as calf muscle pain following exertion suggestive of peripheral arterial disease.

Subjects' height was measured using a measuring tape with subject standing erect against a vertical wall, while weight was measured using a ZT-160 standing weighing scale. BMI was calculated (weight/height 2 in meters). All subjects underwent B-mode ultrasound evaluation of the walls of the common carotid artery (CCA), the carotid bulb (CB), and the extracranial internal carotid artery (ICA).

Ultrasound technique

Ultrasound examination of the carotid arteries was performed using a 7.5-10 MHz linear transducer on a Logic-P5 General Electric ultrasound machine. The subjects were placed in the supine position with the neck slightly extended and head turned away from the side of examination. To obtain a good image, the sound wave was beamed perpendicularly to the arterial surface of the near and far walls of the vessel giving two parallel echogenic lines which correspond to lumen-intima and media-adventitia interfaces [Figure 1] and [Figure 2]. The inner echogenic line plus distance between the lines was taken as the combined thickness of the intima and media (IMT complex). [9] The technique of 'multiple carotid sites measurement' was adopted. [15] Using this approach, on B-mode longitudinal images, the IMT is measured from the far wall of the three main segments of the extracranial carotid arteries on both sides, namely: i) The CCA at 1-1.5 cm proximal to the CB, ii) the CB and, iii) the extracranial ICA.{Figure 1}{Figure 2}

The mean IMT is the average of the three values from the three sites on each side.

Data management

Statistical analysis of the data was done using Statistical Package for Social Sciences (SPSS) software version 17.0 for Windows. Associations between categorical variables were explored using the Chi-square test, while numeric variables were compared with the Student's t-test. Associations were deemed significant if P value were < 0.05.

Study limitations

Several elderly patients had tortuous CCAs and ICAs which made assessment of the IMT for these vessels technically difficult and often prolonged the measurement procedure. However, only data generated from subjects with the requisite complete set of measurement for CIMT on both sides were entered into the data sheet for analysisThere were variations in IMT along the walls of the measured vessels. However, this was addressed by measuring only the far wall, and by averaging the values from the three specified sites of measurement.

 Results



The study population comprised 120 hypertensive subjects with an age range of 21-80 years. Median and mean ages were 50 and 50.61 years (± 10.94), respectively. There were a larger proportion of females (58.3%) than male subjects (41.7%). Most (85.8%) of the participants were above the age of 40 years, with the largest proportion (32.5%) falling within the 40-49 years age bracket.

The mean height, weight, and BMI (±SD) for male subjects were 1.66 ± 0.06 m, 69.36 ± 12.31 kg, and 24.92 ± 3.99 kg/m 2 while values were 1.59 ± 0.07 m, 65.6 ± 10.38 kg, and 25.6 ± 4.49 kg/m 2 for female participants, respectively [Table 1]. The difference in mean BMI values between genders is not statistically significant (P = 0.592).{Table 1}

The mean IMT on the right side was 0.781 ± 0.124 and 0.729 ± 0.130 mm for males and females, respectively. On the left side, mean IMT was 0.779 ± 0.127 and 0.740 ± 0.131 mm for males and females, respectively. Mean CIMT values were lower in females but this was only significant on the right side. The right side shows higher values than the left in the males [Table 2].{Table 2}

As seen from [Table 3], the proportion of the underweight/normal group and overweight/obese group in the male subjects were 54 and 46%, respectively. The mean CIMT values on the right (0.820 mm) and left (0.816 mm) sides were higher for the overweight/obese male hypertensive subjects when compared with mean values for the underweight/normal subjects (right: 0.744 mm and left: 0.740 mm). This difference is statistically significant bilaterally with P values of 0.039 and 0.049 for the right and left sides, respectively. For the females, the proportions of the underweight/normal subjects and the overweight/obese subjects are 54.3 and 45.7%, respectively. This is similar to the distribution in males. The mean CIMT values on the right and left sides for the overweight/obese female subjects were 0.743 and 0.731 mm, respectively. The mean CIMT on the right and left sides for the underweight/normal female subjects were 0.720 and 0.737 mm, respectively. However, there is no statistically significant difference between the two BMI groups in female subjects.

A weak positive correlation is noted between BMI of the male subjects and CIMT on both sides, however this is also not statistically significant, with Pearson's correlation coefficient of 0.252 (P = 0.070) and 0.142 (P = 0.236) on the right and the left sides, respectively. Female subjects also show no statistically significant correlation between BMI and CIMT [Table 4].{Table 3}{Table 4}

Regression analysis, scatter plots, and line of best fit shows no positive or negative correlation between BMI and CIMT on the right or left sides for both genders.

 Discussion



Obesity is defined as an excessive accumulation of fat within the body resulting in an increase in weight beyond that considered desirable for age, height, and bone structure; and is therefore a state of excessive body weight. [16] It can also be defined as a state in which a person's weight is 20% above the expected standard weight. [16] A BMI of 20-24.9 kg/m 2 is desirable. However, individuals with BMI equal to or greater than 25 kg/m 2 and less than 30 kg/m 2 are regarded as being overweight, while those with BMI of 30 kg/m 2 or greater are regarded as obese. [10]

High resolution B-mode ultrasound is noninvasive, simple, safe, inexpensive, precise, and reproducible; and has been used in this study to assess adaptive vascular changes, specifically carotid arterial wall thickening in hypertensive adults in relation to BMI.

The median and mean ages of hypertensive subjects in this study was 50 and 50.61 years (± 10.94), respectively. It was also observed that most of the subjects (85.8%) were aged 40 years and above which is consistent with reports from previous studies which suggest an increased prevalence of hypertension among the middle aged and the elderly in the Nigerian population. [17],[18] The mean height values of 1.66 and 1.59 m recorded for males and females, respectively are also compatible with previous reports from Nigeria. [19] However, the mean weight for this study population of 69.36 and 65.6 kg for males and females, respectively is higher than the African combined average of 60.7 kg (2011). [20] The mean BMI of 24.92 kg/m 2 for males and 25.6 kg/m 2 for females reported in this study are also higher than the Nigerian adult mean value of 22.38 kg/m 2 (23.98 and 21.77 kg/m 2 for males and females, respectively) reported in a previous study. [20] This higher weight and BMI may have been contributory to the hypertensive status of the study population.

CIMT and hypertension

In this study, the lowest mean CIMT value in the hypertensive subjects is 0.729 mm, while the highest recorded mean CIMT is 0.781 mm. There is however a significant variation in CIMT values reported for hypertensive adults worldwide, ranging from 0.762 mm in the United States [21] to 0.969 mm in Nepal. [9] This is probably due to sociodemographic factors affecting study populations in different geographic, economic, and cultural settings. Factors such as diet and consumption habits, living standard, lifestyle, and health practices ultimately influence population health and these same factors may have a role in the prevalence of hypertension and the global variation in the reported CIMT values.

CIMT and gender

The mean CIMT on the right and left sides in this study were higher in hypertensive males than females (but this difference was statistically significant only on the right side. This finding is in agreement with findings by Youn et al., [22] who reported higher CIMT values for middle aged males compared with females in a rural Korean population. However, there are conflicting results on the association between gender and CIMT as some other studies showed no definite gender differences in CIMT measurements of hypertensive subjects. Sorof et al., [23] in a study of hypertensive adolescents in the Unites State of America (USA) reported that CIMT did not vary significantly by gender. Freitas et al., [13] in a study of Brazilian hypertensive adults also documented similar CIMT for both sexes. The recorded higher mean CIMT in hypertensive males when compared to females in this study may be associated with the generally higher prevalence of hypertension among males in this community. [17],[24] Also, since hypertension predisposes to arterial wall adaptive changes, this may account for the significant association in males. Further studies with a larger sample size will be required to make a more definitive statement on this finding.

CIMT and BMI

The mean CIMT values for the overweight/obese male subjects (BMI ≥ 25 kg/m 2 ) in this study are noted to be higher than the mean CIMT values for the underweight/normal male subjects (BMI ≤ 24.9 kg/m 2 ). The difference in values between the two groups (0.820 and 0.816 mm vs 0.744 and 0.740 mm on the right and left sides, respectively) is statistically significant bilaterally. However, the female subjects showed no statistically significant variation in CIMT values between the overweight/obese and the underweight/normal groups.

The finding in male subjects is in agreement with reports from previous studies. [25],[26],[27] Which show a positive association between BMI and CIMT. Holland et al., [25] reported higher CIMT values among male hypertensive and obese individuals in a South African study population. In that study and amongst the same study population, higher CIMT values were also reported for subjects who had some risk of metabolic syndrome. Metabolic syndrome has been linked to obesity, hypertension, low high density lipoproteins (HDL), high low density lipoproteins (LDL), and high triglyceride (TG) levels. Gonzalez et al., [26] also reported a significant association between BMI and CIMT in young adults. Similarly, Leite et al., [27] reported higher mean CIMT values in overweight and obese patients, when compared with the underweight/normal group.

Weight, BMI, and CIMT

The lack of association between CIMT and weight for the female subjects in this study may be due to the relatively lower mean CIMT values and lower weights recorded in females compared with the males. This study also shows only a weak positive correlation between weight and BMI on the one hand, and with CIMT values on the other, on the right and left sides for males. This is however not statistically significant. Also, no definite correlation between weight, BMI, and CIMT is noted for the female subjects. These are at variance with some previous studies from which positive BMI and CIMT correlation were reported. Youn et al., [22] studied the correlates of mean CIMT in a Korean rural middle-aged population, and reported a definite association between CIMT and obesity. Also, Leite et al., [27] reported that CIMT is positively associated with an increase in BMI in adolescents, even in moderate overweight ranges, independent of age or gender.

The findings in this study may be due to the fact that a larger proportion of subjects of both genders had BMI values within the underweight/normal range (≤24.9 kg/m 2 ) which is associated with comparatively low CIMT values.

 Conclusion



This study demonstrates significantly higher CIMT values for the overweight/obese males with primary hypertension, compared with those that are underweight/normal. However, no statistically significant difference was observed between the two groups for the female subjects. There is however a very weak positive correlation between weight and BMI with CIMT for the male subjects.

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