The Body Mass Index, Waist Circumference and Blood Pressure of Postmenopausal Women in Zaria, Northern Nigeria

ABSTRACT

Changes in sex hormone during the menopausal transition are thought to have an important impact on weight gain. Obesity is known to be a determinant of health and disease; especially cardiovascular diseases. We studied the waist circumference, body mass index and its correlation with the blood pressure of a sample of menopausal women in Zaria. The height (m), weight (kg), waist circumference (cm) and blood pressure (mmHg) of the women was assessed using standard methods, while the body mass index (BMI ) in kg/m² was calculated. 165 subjects participated in the study, 77 were premenopausal women while 88 were postmenopausal women with mean ages 25.51±0.60yrs and 53.59±0.65yrs respectively. The subjects were selected based on some exclusion criteria. Postmenopausal women were more likely to be overweight (mean BMI 25.96±0.53kg/m² ) compared with their premenopausal counterparts (23.13±0.57kg/m² ); p<0.001. The menopausal women also had a higher waist circumference (93.04±1.60cm) as compared with the premenopausal women (78.87±1.30cm); p<0.001. Only 73.86% of the postmenopausal women had a BMI ≥ 25kg/m² whereas the prevalence of central obesity was 79%. However, there was a significant positive correlation observed between waist circumference and the body mass index (p<0.05). These findings suggest that obesity is prevalent among the menopausal women while the waist circumference was found to be a better measure in assessing obesity and thus cardiovascular risk among menopausal women in Zaria. We recommend the establishment of menopause clinics for early identification of women at risk and hence commencement of intervention.

Key words: Body Mass Index, Blood pressure, Menopause, Obesity, Waist circumference Zaria.

INTRODUCTION

The prevalence of obesity is rising in developed and developing nations and studies have demonstrated a role for weight gain in morbidity and mortality risk (Huang et al, 1997; Flegal et al., 2005). Body composition changes become evident as women transitionthrough menopause. These changes include an increase in overalland central adiposity, especiallyvisceral adipose tissue, and a decrease in total and centrallean tissue mass (Poehlman and Tchernof, 1998). In particular, central adiposity in postmenopausal women, as measured by the waist circumference, is recognised as an independent risk factor for developing insulin resistance, dyslipidemia, breast cancer, hypertension and other cardiovascular diseases (Huang et al, 1997). The body mass index (BMI) is commonly utilised to represent the degree of body fat, it however does not capture body fat distribution which the waist circumference does. Studies indicate that even with a “normal” BMI, those with an elevated waist circumference can have a two fold increase in cardiovascular disease risk (Pischon et al., 2008). The current thrust in health is preventive medicine. There is however a dirge of menopause clinics in the country where monitoring and health education can be instituted. Hence the body mass index and waist circumference serves as an easy to perform, non-invasive and cost effective measurement that can be used in monitoring at primary health centres and out patient clinics. There is paucity of data on the role of obesity in cardiovascular mortality and morbidity in African postmenopausal women. No study has been reported in Zaria a semi-urban population in a developing country (Nigeria).Given the impact of obesity on mortality and morbidity, we aimed at determining the waist circumference, body mass index, its correlate with blood pressure and the prevalence of obesity in a sample of postmenopausal women in Zaria.

MATERIALS AND METHODOLOGY

Zaria town is located in the Savannah region of Northern Nigeria with a cosmopolitan population. Questionnaires were administered and anthropometric measurements taken from 165 Nigerian women resident in Zaria in a cross-sectional prevalence study. 88 of the women were postmenopausal aged between 40 – 65years, while 77 of the women were pre-menopausal(15 – 35-yr). Postmenopausal women selected were at least 1 year amenorrhoeic due to a natural cause and were aged 40-64 years. The premenopausal women were regularly menstruating, non-pregnant, non-lactating with no use of hormonal contraception for at least 1 year. Women who were diabetics, hypertensive, who smoke cigarette, drink alcohol, amenorrhoeic due to hysterectomy or cessation of periods other than by a natural cause were identified and excluded from the study.

Weight (kg) to the nearest 0.2kg was measured with a calibrated scale. The height (in meters) of the subjects was determined with a stadiometer (Harpenden) to the nearest 0.5cm. The BMI was calculated as the weight (kg) divided by the height (m) squared (kg/m² ). Underweight was defined as a BMI <18.5kg/m², normal BMI as >18.5kg/m² -24.9 kg/m², overweight as BMI between 25 - 29.9 kg/m², obese as BMI > 30 – 39.9 kg/m² and BMI ≥ 35 kg/m² was considered as morbid obesity. Using a flexible metric tape the waist circumference (in centimetres) was assessed at a point midway between the lowest rib and the iliac crest using flexible metric tape (Butterfly, China), with the subject standing. Blood pressure measurements (in mmHg) were taken with the patient seated using a mercury sphygmomanometer (Acosson, A. C. Cossor & Son (surgical) LTD, London)) and a stethoscope (3M Littmann Classic II S.E. Stethoscope, U.S.A).

The study was undertaken after obtaining consent from the participants and approval from the Ethical Committee on Human Research of Ahmadu Bello University, Zaria.

Results were presented as mean ± SEM and data analysed using Student’s t-Test. Correlation coefficient was used to find the relationship between the waist circumference, BMI and other variables. Results were considered statistically significant with p<0.05.

RESULTS

Table 1 displays major characteristics of premenopausal and postmenopausal women. There was an approximately 28-yr difference in the mean age between postmenopausal and pre-menopausal women. The parity, BMI, waist circumference, systolic blood pressure, diastolic blood pressure and prevalence of central obesity was higher in the postmenopausal than premenopausal women.

Figure 1 summarises the frequency distribution of the BMI of the menopausal women. Women with a normal BMI constituted 10.23% of the population while a higher percentage of the menopausal women had an above normal BMI (73.86%) with 15.91% being underweight.

Table 2 displays the correlation between parity, BMI, diastolic blood pressure, systolic blood pressure and waist circumference for postmenopausal women.Significant positive correlations were observed for menopausal age and parity, parity and diastolic blood pressure and between waist circumference and the BMI.

Table 1: Anthropometric data of control and menopausal women

illustration not visible in this excerpt

p<0.05*

illustration not visible in this excerpt

Figure 1: The frequency distribution of the body mass index (BMI) of the menopausal women.

Table 2: A correlation matrix for menopausal women

illustration not visible in this excerpt

BMI=body mass index, DBP=diastolic blood pressure, *=p< 0.05, **= p <0.01

DISCUSSION

The BMI of the menopausal women in this study (25.96±0.53kg/m² ) was within the overweight range and also higher than that of the control group (23.13 ±0.57kg/m², p<0.001). Similar findings were observed in a study of post menopausal women in Calabar, Nigeria (Usoro et al., 2007). Where a mean BMI of 23.31kg/m² and 25.97kg/m² for premenopausal and post menopausal women respectively were determined (Usoro et al., 2007). Gavaler and Rosenblum, (2003), reported an increase in BMI with menopause and identified smoking, moderate drinking, fat as percent of total calories, neuro-endocrine factors, and being Black or Asian as significant predictors for increased BMI. The weight gain was thus different from the age related difference. Factors implicated include a decrease in resting metabolic rate, decreased physical activity, depression and an increase in insulin levels due to associated insulin resistance (Poehlman et al., 1995). Long-term lifestyle dietary and physical activity intervention have been found to prevent weight gain and central adiposity in postmenopausal women (Simkin-Silverman et al., 2003). Another factor implicated in the menopausal weight gain is a decrease in resting energy expenditure with oestrogen loss during the menopause (Poehlman and Toth, 1995). Though the resting energy expenditure of African-Americans, Caucasian and Nigerian population (postmenopausal women) was found to be indistinguishable there was however a greater incidence of obesity in the former two groups than in the Nigerian postmenopausal woman. However, a racial difference in leptin levels (20% lower in African-American) is thought to explain the higher incidence of obesity in the African-American postmenopausal woman (Ebersole et al., 2008; Nicklas et al., 1997). Crawford et al (2000)reported a contrary finding.

Only 10.23% of the postmenopausal women were of normal BMI, 15.91% were underweight while 31.82%, 39.77% and 2.27% were overweight, obese and morbidly obese respectively (fig. 1). Implying that, 73.86% of the women had an above normal BMI. The higher BMI in menopause is associated with increased levels of estrone and an increased risk of breast cancer (with larger tumours) and a higher age at natural menopause (Asseryanis, et al., 2004; Akahoshi et al., 2002). Despite these risks, in most Nigerian cultures, the matronly or overweight figure is commonly considered as more befitting for older aged ladies. Concerted efforts need to be made to sensitise individuals to control the prevalence of obesity considering its role as a risk factor for cardiovascular diseases, diabetes mellitus and metabolic syndrome.

[...]