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Relationship between measures of obesity and Atherogenic lipids among Nigerians with hypertension

Olamoyegun A. Michael1, Fawale M. Bimbola2, Oluyombo Rotimi3

1.Department of Internal Medicine; Endocrinology, Diabetes & Metabolism Unit,; LAUTECH Teaching Hospital, and College of Health Sciences, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.

2Department of Medicine, Obafemi Awolowo University Teaching Hospital Complex, and Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.

3Department of Medicine, Federal Medical Centre, Ido-Ekiti, Ekiti State, Nigeria.

Corresponding Author: Olamoyegun A. Michael; e-mail: dryemi@yahoo.com


                                                                 Abstract

Aim

To determine the relationship between measures of obesity and serum lipids levels among hypertensives.

Methods

This is a cross-sectional study in which participants newly diagnosed with essential hypertension formed the study population. Demographic and anthropometric data including weight, height, waist and hip circumferences were obtained. Fasting serum lipids including total cholesterol, high density lipoprotein cholesterol (HDL-C) and triglycerides (TG) were measured. Low density lipoprotein cholesterol (LDL-C) was calculated by Frieldewald formula. Statistical analysis was done to determine the relationship between anthropometric indices and lipid profile levels.

Results

The study population consisted of 124 male and 290 female subjects with a mean age of 66±16.95years (range, 30-100years).The female subjects were older than the male subjects (p = .020). Eighty five percent, 58.5% and 30.7% of the study population had abnormal waist circumference (WC), abnormal waist-hip ratio (WHR) and body mass index (BMI) >25kg/m2 respectively. Decreased HDL-C (70.1%) was the commonest lipid abnormality found followed by elevated LDL (6.0%). None of the anthropometric indices independently predicted abnormal lipid levels; older age and female sex independently predicted occurrence of at least one serum lipid abnormality.

Conclusion

None of the measures of obesity independently predicted abnormal lipid levels in newly diagnosed hypertension. Female gender, older age and systolic blood pressure were independently associated with abnormal serum lipids.

Keywords: Anthropometric indices, obesity, lipid profile, hypertension


© 2019 The College of Medicine and the Medical Association of Malawi. This work is licensed under the Creative Commons Attribution 4.0 International License. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)


Introduction

The prevalence of hypertension is projected to increase by 7.2% from the 2013 estimates by 20301. It is one of the highest contributing cardiovascular diseases that has a lot of associated contributing factors among which are dyslipidaemia and obesity (measured with abnormal body mass index(BMI), waist circumference(WC), and waist-Hip ratio(WHR)2. Although, there are increasing efforts by world health governing bodies to stem the prevalence of hypertension and associated risk factors in Africa, the prevalence of hypertension still ranges from 6% to more than 48% in different rural, semi-urban and urban settlements3–5.

Most African settlements are emerging semi-urban settlements and these accounts for more than half of the region’s population6. Nigeria, being a strategically placed country in the West African sub-region is not left out of the scourge of Non-communicable diseases including hypertension and its modifiable risk factors as they are responsible for at least 20% of all deaths and constituting about 60% of medical wards hospital admissions in most tertiary health institutions7,8.

The mechanisms of hypertension in obese individuals were poorly until recently. Evidence accumulating indicate a close interaction of visceral adipose tissue and disrupted neurohormonal mechanisms such as adiponectin, leptin, resistin, tumour necrotic factor (TNF), and IL–6 caused by increased adiposity9–11. Increases in cardiac output without corresponding decrease in systemic vascular resistance characteristic of obesity also probably contributes to the aetiology of the hypertension in obesity. On the other hand, the association of dyslipidaemia with hypertension that has been termed ‘Lipitension’ is caused primarily by the endothelial damage and loss of physiological vasomotor activity caused by atherosclerosis which usually goes concomitantly with dyslipidaemia12. Obesity and dyslipidaemia have been reported in several studies as diseases that go together and it not uncommon for both to coexist in the same individuals.

The purpose of this study was therefore to evaluate the association between obesity and dyslipidaemia in newly diagnosed hypertensive individuals living in a semi-urban community.
Materials and Methods

This was a cross sectional study of dyslipidaemia and obesity in newly diagnosed hypertensives living in semi–urban communities located in Ekiti state, Nigeria. The subjects were aged ≥ 30 years and the study was carried out between January and May 2013. The  sample was a subset of a larger sample for the determination of cardiovascular assessment in semi-urban communities. The subjects were asked basic questions about their age and other sociodemographic data.  The instrument used was the WHO STEPS (II) questionnaires13. Clinical evaluation, blood and urine sample collection were carried out at designated places in the communities such as churches, mosques, town halls, health centres, and other convenient places. Prior notices and permissions were obtained from traditional rulers, opinion leaders, church and mosque leaders. Informed consent was obtained from all participants.

Anthropometric and Blood Pressure Measurements

Height

This was measured using a portable stadiometer. The subjects were asked to be barefooted, arms by their sides and to look straight backing the vertical board14.  The height was recorded to the nearest 0.1cm.

Weight

This was taken while in light clothing with the subject standing in the centre of a standard portable bathroom weighing scale’s platform; weight was recorded to the nearest 0.1kg

Waist Circumference

While subject was standing comfortably with both feet about 25 – 30 cm apart, measurements were taken with a tape measure at a point midway between the inferior margin of lowermost rib and the iliac crest in a horizontal plane14. The waist circumference was measured to the nearest 0.1cm at the end of normal expiration.

Hip Circumference

Measurements were taken using the tape rule.  It was measured with the greater trochanters of the femur as reference points. The measurement was the nearest 0.1cm.

Blood pressure

Blood pressure was measured according to the guideline presented in the Seventh report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High blood pressure(JNC-7)15, Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured in the left arm after participant have been seated for at least 5 minutes.  Electronic blood pressure monitor (Omron M X2 Basic, Omron Health Care Co. Limited, Kyoto, Japan) that has been validated by the British Hypertension Society was used with appropriate sized cuff. The length of the blood pressure cuff bladder was about 80%, and width at least 40% of the circumference of the upper arm.BP was taken twice and if difference was more than 10mmHg, the third reading was taken at an interval of about 5 minutes.

Anthropometric information was obtained using a portable stadiometer for the measurement of height to the nearest 0.1 cm and a portable weighing scale was used to measure weight to the nearest 0.1 kg. Other clinical parameters like blood pressure was also measured using standard guidelines.

Clinical Evaluation

Three (3) mls of blood samples were collected after 8-12hours overnight fast from each patient into plain bottles for lipid profile analysis – total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), and triglycerides (TG). However, low density lipoprotein cholesterol (LDL-C) was calculated using Frieldward equation16. The samples were stored in a -80C freezer till batch analyses were done in the laboratory.

Dyslipidaemia was defined according to the Adult Treatment Panel (ATP)III17as raised TG level ≥ 1.7mmol/L, reduced HDL-Cholesterol – < 1.03mmol/L in males and < 1.30mmol/L in females, LDL – C level higher than 3.37 mmol/L and/or TC level ≥ 5.2mmol/L. Abnormal WC, WHR and BMI were taken as ≥ 94cm in men and ≥ 80cm in women; > 0.90 for men and 0.85 for women; and ≥ 25 kg/m2 across sexes respectively.

Statistical Analysis

All the data were recorded and analyzed using the Statistical Package for Social Sciences software (SPSS Inc, Chicago, IL version 17). Continuous variables  including age, systolic blood pressure, diastolic blood pressure, lipid profile, BMI, WC, and WHR were presented as mean ± standard deviation and compared across sexes while other categorical variables were expressed in frequencies and percentages with p value < 0.05 taken as statistically significant. Pearson correlation was used to test for association between continuous variables.  Logistic regression models were constructed using presence of at least one lipid abnormality, abnormal TC, LDL-C, HDL-C and TG as the dependent variables respectively and age, sex, blood pressure and indices of body adiposity as the independent variables respectively. Ethical clearance was obtained from the ethics and research committee of Federal medical centre, Ido-Ekiti.

Results

A total of 124 male and 290 female  hypertensive patients were included in this study with age ranging between 30 and 100 years (Mean = 66.00 ± 16.95 years).  The female subjects were older than the male subjects (67.18 ± 14.40 years vs. 63.22 ± 18.89 years; p= .020). There were also significant gender differences in WC, LDL-C and TG (Table 1)

Among the subjects, a disproportionately higher number of females have both abnormal measures of obesity and dyslipidaemia. Two hundred and eighteen females (75.2%) had abnormal WC as compared to twenty four (19.4%) of the males. More than 30% of the study population had BMI >25kg/m2. In 85% of cases, WHR was abnormalLipid subfraction analysis showed low HDL-C to be the commonest abnormality, noted in 70.0% of the study population, followed by elevated LDL-C levels noted in 6.0% (Table 3). Of the dyslipidaemias, 6.6%, 75.9%, 7.6% and 5.9% of the females had high TC, low HDL, high LDL and high TG respectively. Of these, only low HDL and high LDL were significantly higher than that of males (p= < 0.001, p= 0.030). Figure 1 shows the prevalence of the various lipid abnormalities. Among the participants, 310 (74.9%) had at least one form of lipid abnormality. Also, 104 (25.1%) had no form of lipid abnormality. More than a tenth (12.9%) of those with dyslipidaemia had more than one lipid abnormality in various combinations. Elevated TG and low HDL-C 14 (4.5%) was the most frequent dyslipidaemia combination, followed by elevated TC and elevated LDL-C 11 (3.5%) combination. Logistic regression analyses revealed increasing age (OR = 1.017, 95% CI = 1.003 – 1.032, p = .015) and female sex (OR = .376, 95% CI = .235 – .602, p =<.001) as the only independent predictors of at least one serum lipid abnormality (Table 6). When TC, HDL, LDL and TG were made the dependent variables respectively, current systolic blood pressure was the only predictor of high TC (OR = 1.071, 95% CI = 1.001 – 1.033, p = .031); female sex was the only independent predictor of abnormal HDL (OR = .407, 95% CI = .260 – .635, p = .000) and LDL (OR = .305, 95% CI = .089 – 1.037, p = .057) while TG had no independent predictor. Abnormal total cholesterol and at least one lipid abnormality were associated with a higher systolic BP and waist circumference respectively on bivariate analysis (Tables 4 and 5) but these relationships disappeared when other factors were adjusted for.

Discussion

The study examined the relationship between measures of obesity and lipid profiles among adults with hypertension. Obesity and hypertension are two interrelated cardiovascular disease risk factors that usually co-exist together. Decrease in adiposity is one of the most effective preventive measures in decreasing not only the blood pressure but also the overall cardiovascular risk. In this study, a relatively high proportion of subjects were obese as measured by different anthropometric indices and all obesity indices were significantly higher in the female compared to the male subjects. The higher prevalence of obesity among the female subjects has been partly attributed to physical inactivity, since they are generally engaged in occupations  such as trading where they spend most of their times sitting down in their shops and engaging in predominantly sedentary activities. This strong association between obesity and sedentary activities such as trading has been supported by Afolabi et al18 in South-western Nigeria.

The prevalence rate of 75.1% of dyslipidaemia in this study is much higher than 58.9% reported by Akintunde et al19 in South-Western Nigeria among hypertensive and 64% reported by Adamu et al20 in North-Central Nigeria. Lipid abnormalities noted in the present study revealed reduced HDL as the most common lipid abnormality, followed by increased LDL. This is in conformity with other Nigerian studies19,21,22 who also found a very high prevalence of low LDL-C in their participants, as the most prevalent lipid abnormality. Our findings, however, differ from those in Caucasians, where reduced HDL-C was said to be uncommon in ATP III [17]. This disparity might be due to the environmental conditions, socioeconomic status, and genetic make-up of our study population. Isolated low HDL-C is said to be a relatively common baseline lipid abnormality among the general population in Nigeria, and the presence of hypertension only escalates it23. The role of HDL-C at improving cardiovascular risks, though not fully elucidated, has been shown to be due to its effect as a potent anti-inflammatory and anti-oxidant that inhibit the atherogenic process24,25.

Our study has shown, that among commonly used anthropometric indices, none was good enough to predict abnormal lipid profile. However, it showed significant association with diastolic blood pressure (DBP), with the waist circumference (WC) having more association (p=0.001) than waist-hip-ratio (WHR), p=0.035 in a sample of semi-urban dwellers in South-western Nigeria.  A similar finding was observed by Okpara et al26 who found abnormal lipids to be strongly associated with both systolic and diastolic BP. The significant association between WC and WHR with DBP is consistent with the established evidence that a direct association exists between obesity and blood pressure27. There was no significant alteration in lipid profiles with obesity among participants, which implies that obesity may be a less important factor in predicting abnormal lipid profiles in this population. This finding is in keeping with previous reports of lack of association between lipid abnormalities and measures of obesity26 but contrary to some studies which have shown positive association between lipid levels and adiposity23,28.

To our knowledge, this is the first study that has compared three commonly used anthropometric indices to predict dyslipidaemia among hypertensive in a population of semi-urban dwellers of Nigeria. Our focus was to compare various indices of obesity among hypertensive in terms of their ability to predict dyslipidaemia.

In conclusion, the findings in this study have suggested that obesity in is particularly significantly higher among female sub-urban dwellers with hypertension compared with their male counterparts and is not an important predictor of abnormal serum lipid levels.  Older age, female gender and higher SBP were the most important and independent predictors of abnormal lipid levels in this population with essential hypertension. Also, there was positive correlation between WC and WHR and DBP.

The strength of the study was based on the fact that it was a community-based study with a moderate number of participants. The cross-sectional design of this study limits the freedom with which its results regarding causal relationships can be interpreted. Hence, prospective longitudinal studies with a larger sample sizes are therefore suggested. Finally, we did not calculate novel lipid ratios, which may also be abnormal even in the presence of insignificantly abnormal lipids.          
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