Prevalence and risk factors of overweight and obesity: findings from a cross-sectional community-based survey in Benin

Background: Data on overweight and obesity in general population in Benin is scarce. This study aimed therefore to assess prevalence and risk factors of overweight and obesity in Benin. Methods: The study consisted of a cross-sectional survey, using the World Health Organisation (WHO)’s instrument for stepwise surveillance (STEPS) of non-communicable diseases risk factors. A five stage random sample of 25 to 64 years old male and female adults living in Benin participated in structured interviews and their size, weight and blood pressure were measured according to standardized procedures. Prevalence and means were computed with their 95% confidence interval and standard error respectively, taking into account the sampling design. Prevalence was compared by Khi2 and means by Student’s t test. Univariate and stratified by gender multivariate polytomous logistic regressions were performed to identify socio-demographic and physical risk factors of overweight and obesity. Results: A total of 6,773 adults participated in the study. About 50.50% of the participants were male. The overall prevalence of overweight and obesity was 19.20% (95% CI 17.91; 20.66) and 7.25% (95% CI 6.34; 8.14) respectively. The prevalence of high risk abdominal obesity was 15.48% (95% CI 15.45; 15.50). The prevalence of overweight (22.41% vs. 15.99%) and obesity (10.68% vs. 3.61%) was significantly higher in females than males. Likewise, the prevalence of abdominal obesity was significantly higher in women (27.39%) than in men (2.73%). After controlling for confounding factors, risk factors of overweight and obesity in both women and men were older age, primary and high school/university education levels, occupation, dwelling and department. Conclusion: Our findings suggested that overweight and obesity are common in Benin. However, some differences were noted between women and men as regards socio-demographic variables. These findings call for more in-depth studies. Moreover, policies and programmes targeting the identified risk factors and high risk abdominal obesity may prove helpful in reducing the prevalence of overweight and obesity in Benin.


Background
In most of the African developing countries, attention is focused on communicable diseases mainly HIV/AIDS and malaria. As a result, non-communicable diseases are mostly neglected in spite of the growing concern caused by the rise of their prevalence. For instance, prevalence of overweight and obesity has been steadily increasing [1][2][3]. Many studies have shown the link between excess body weight and increased risk for cardiovascular disorders, [4] type 2 diabetes, dyslipidemia, some cancers and gallbladder diseases [5][6][7]. Prevalence of obesity and overweight is gradually increasing in developing countries as people experience changes in diet and physical activities patterns due to the influence of the western culture [2,8].
According to the World Health Organisation report, more than one third of women and a quarter of men in Africa are overweight, and these proportions are expected to increase by 41% and 30% respectively over the next ten years. Recent trends in urbanization in developing countries and the globalization of the food market contribute in changing people's behaviour and lifestyle. Changes in lifestyle, associated with the nutrition transition from traditional to modern habits, have led to the emergence and progression of overweight and obesity [7,9]. Besides, more emphasis was put on undernourishment and food security than obesity which was neglected [2]. Despite the importance of the issue, data on obesity and overweight in Africa in general and in Benin in particular is scarce. Indeed, the study by Sodjinou et al., [10] conducted in a random sample of 25 to 60 years old urban adults dealt only partially with obesity. Our study was entirely devoted to the issues of overweight and obesity. Its objective was to determine the prevalence and the risk factors of overweight and obesity in the communities in Benin using a cross-sectional survey.

Context
Benin is a Francophone country, located in West Africa. With a Gross National Product of 683US$, Benin is one of the poorest countries in the world. According to the general population census of 2002, Benin population was estimated at 8

Study design and sampling
The present study was a cross-sectional one of adults aged 25-64 years conducted on overweight and obesity risk factors in Benin using the WHO STEP instrument [12]. The sample size was calculated based on prevalence of hypertension of 27.8% [13] with the expected precision of ±1.5%. Each district selected was considered as a cluster. A cluster effect of 2 was therefore applied to the sample, as recommended by WHO for sociodemographic data [14]. Each cluster comprised of 114 individuals. A probabilistic sample of 6,853 adults aged from 25 to 64 was selected to participate in the study.
The probability proportional to size sampling was used to select the study sample [15]. Sixty of the 546 districts of Benin were randomly selected and smaller geographic units within the districts recognized as zones or villages were identified and listed for further random selection. The selection of individuals within each neighbourhood or village was based on Kish's method [16] which caters for gender and age. It has been done as follows: the investigator placed himself at the centre of the city or village and chose a random direction. In the chosen direction he numbered all the households, then selected the first household to be investigated. It was processed that way until the number of individuals in a given district was completed.
People having lived in the zone for at least six months and having given informed consent forms were included in the study. People unable and/or unwilling to respond to the questionnaire and pregnant women were excluded from the study.

Data collection
We used the WHO STEPS instrument [12] to collect data. The investigator performed a face to face structured interview using a questionnaire encompassing socio-demographic characteristics, behavioural habits and history of hypertension. Participants' blood pressure was then measured three times with a standard digital sphygmomanometer (Omron Healthcare, Inc., Bannockburn, lll) while he/she was in a sitting position [12] after having rested for at least 15 minutes. The average of the last two readings was used in the analysis. Subjects were considered to have hypertension if their systolic blood pressure was at least 140 mm Hg, their diastolic blood pressure was at least 90 mm Hg, or they were being treated for hypertension [17]. Weight and size of the respondents were measured during the investigation. Weight was measured with a precision of 100g with electronic weight and the precision of size was 1 cm. The body mass index (BMI) was calculated by dividing weight in kilograms by size in meters squared. Subjects were considered as underweight/undernourished having chronic energy deficiency if their BMI was lower than 18.5 kg/m 2 ; not overweight, if their BMI was higher than 18.5 kg/m 2 and lower than 25 kg/m 2 , overweight if their BMI was equal to 25 kg/m 2 and lower than 30 kg/m 2 and obese if their BMI was equal to 30 kg/m 2 or higher. Abdominal obesity was defined as waist circumference of ≥102 cm in men and ≥88 cm in women based on criteria suggested by WHO [18]. Information on fruits and vegetables intake was collected through two items: the number of portions of fruits and vegetables equivalent to 80 g each taken and the number of days of intake per week. Surveyor helped the respondents by showing them a bowl and pictures depicting a portion of 80 g. Intake of 5 portions of 80 g of fruits and/or vegetables each day was considered as sufficient and otherwise insufficient.

Statistical analysis
Complex survey analysis methods [14] were used to determine prevalence of obesity and overweight in each group, taking into account the sampling design and the sampling weight of each participant which was calculated as the inverse of the probability of selection of that particular participant. We hypothesized that overweight and obesity were associated to gender, age, education level, occupation, dwelling, fruits and/or vegetables intake and department. Univariate and multivariate analyses were performed using STATA 9.2 software (STATA Corp LP, College Station, Texas). The univariate analysis was carried out to evaluate each independent variable for its unadjusted association with overweight or obesity. All independent variables significantly associated to overweight or obesity (p<0.05) were included in multivariate analysis using polytomous logistic regression to evaluate factors associated with overweight or obesity. The multivariate logistic regression doi: 10.7243/2052-5966-2-3 was done separately for women and men.

Ethical considerations
The authorization to perform the study was obtained from the Ministry of Health in Benin. The study objectives were clearly explained to participants who gave their informed consent. Data was processed anonymously and confidentially. Researchers kept their promise to widely disseminate the results of the study within health sector partners and the community.

Results
A total of 6,773 persons agreed to participate in the study: 3,353 (49.5%) women and 3,432 (50.5%) men. The response rate was therefore 98.83%. Average age of the sample was 43 Figure 1 displays distribution of BMI rates according to gender. Chronic energy deficiency was equivalent in men and women and normal weight was higher in men. Conversely, overweight and obesity were higher in women than in men. In the population, the crude prevalence of overweight and obesity was 19  Prevalence of high blood pressure was 27.87% (CI95% 26.33%; 29.41%) and there was no significant difference between men (27.19%) and women (28.51%) (p=0.3996). The prevalence of overweight in women was significantly higher than in men (p<0.001). The prevalence of obesity in women was threefold higher than in men (10.74% vs. 3.63% and p<0.001). Prevalence of abdominal obesity was significantly higher in women (27.39%) than in men (2.73%) (p=0.01). Table 1 shows the results of the univariate analysis. Women were significantly more at risk of being overweight (OR=1.68; p<0.001) or being obese than men (OR=3.55; p<0.001). The risk of being overweight or obese significantly increased with age (p=0.001).
The level of education was a risk factor for overweight and obesity (p=0.001). Indeed, people with high school/university levels of education were significantly more at risk of being overweight (OR=1.64; p<0.001) and obese (OR=2.23; p<0.001) as compared to illiterate people. With regards to profession and as compared to civil servants, independent workers were less likely to be overweight (p=0.001) or obese (p=0.021). Apprentices, housewives and other professions were less likely to be overweight (p=0.017; p=0.039; p=0.001 respectively). Housewives and other professions were less likely to be obese (p=0.039 and p=0.002 respectively). Fruits and vegetables intake was not significant factor for overweight (p=0.777) or obesity (p=0.164). Living in urban areas was a risk factor to be overweight (OR=1.95; p<0.001) or obese (OR=3.24; p<0.001) as compared to people in rural areas. People living in Oueme were more likely to be overweight (OR=1.82; p=0.006) or obese (OR=2.47; p=0.038). People living in Littoral presented a higher risk of being overweight (OR=3.08; p<0.001) or obese (OR=4.98; p<0.001). People living in Collines were significantly more at risk of being overweight (OR=1.84; p<0.004).
Multivariate analysis for women (

Discussion
Our study was based on the STEPS approach recommended by WHO for screening and surveillance of non-communicable diseases risk factors. The prevalence of obesity in our study is similar to that found in Congo (8.6%) in 2004, Nigeria (8.8%) [19,20], Mauritius (10%) [21], Algeria (9%) [22] and it was consistent with the prevalence found by Abubakari et al.,[20] in their meta-analysis. It is two times higher than in Eritrea (3.3%) and half of the prevalence rate found in Cameroon (18%) in 2004 [20]. A study in southern Morocco has reported a prevalence higher than our findings, 30% for overweight and 49% for obesity [23]. The prevalence of obesity in the Democratic Republic of Congo (5.7%) [24] is lower than our findings. The dietary patterns specific to each country could explain the disparity in the prevalence rates of obesity. There is an increasing prevalence of obesity not only in industrialized countries but also in developing countries [25][26][27][28][29]. This is the case of Tanzania, where the prevalence of obesity increased from 3.6% in 1995 to 9.1% in 2004 [30]. As described in the literature, gender is a demographic factor associated with the prevalence of obesity. This trend was confirmed in our study. Indeed, a statistically significant difference was observed by gender. Thus, female subjects were significantly more obese than male. This difference was also found in several investigations in Tunisia [31], in Ghana in 2003 [32] and South Africa [33]. It could be related to the influence of cultural factors. Indeed, female obesity is seen as a sign of wealth and beauty in the African cultural context. Similarly, the influence of behavioural and psychosocial factors has been demonstrated to explain the importance of obesity in women [34]. Furthermore, it has also been reported in the literature that the prevalence of obesity and overweight increased with age [35,36]. This feature of the prevalence of overweight and obesity was confirmed in our study.
Prevalence of obesity was significantly associated with higher education in men as well as in women. Except for cultural factors discussed earlier, socioeconomic factors could explain this situation. Indeed, people with higher education represented only 12% of the study sample. Those people benefit usually from the best opportunities in public services and in private business, are wealthier, live in urban areas and adopt western way of life combined with a very low level of physical activities.
Prevalence of obesity was higher in urban than rural areas. A survey conducted in 2007 in urban Benin reported a prevalence of 18% [10]. The same observation was made in Eritrea in 2005 [37] and the Congo in 2007 [38]. The socioeconomic conditions in these countries do not favour the adoption of healthy behaviours and changes in lifestyle. In Benin, there is a tendency to have a diet rich in fat and low in fruits and vegetables.
Increasing urbanization and production patterns in Africa in general, and in Benin in particular are evolving towards the Western model. It involves a change in lifestyle with unbalanced meals, stress, decreased physical activity due to more sedentary occupations and the increasing use of motorized transport [39,40]. The inadequacy or lack of sports facilities in cities increased the population's settled way of life. Conversely, in rural areas, heavy physical labour is almost permanent and does not offer a lot of development opportunities and suitable periods of rest [6,41]. Such a situation may trigger the emergence of non-communicable diseases and pose a threat to sustainable health.
At the departmental level, the prevalence of obesity was higher in Littoral (20.38%) than in Alibori (5.15%), Atacora (4.45%), and Donga (5.16%). This difference could be explained by the fact that Littoral is more urbanized than Alibori, Atacora and Donga. These areas are mainly mountainous areas and people have different agricultural and diet habits. The Littoral department includes the economic capital of Benin, Cotonou, which is the most developed and where people's lifestyle is similar to the one in the Western world.
Hypertension and obesity are closely linked, but in our analysis, we did not consider hypertension as an associated factor to obesity, because in the literature it is not known exactly which of the two led to another [42]. However, we used hypertension to describe the population on which we worked. Indeed people who were overweighed or obese were at risk to have hypertension compared to normal people (OR=1.53 (p<0.001) and OR=2.57 (p<0.001) respectively). Dyer et al., Scholtee & Stunkand, Stamler et al., showed the close relationship between hypertension and obesity or being overweight [43][44][45].
An obese person has the blood pressure higher than non-obese, which significantly increases the cardiovascular risk. We noticed this in our study, where the diastolic blood pressure's mean were 77.59 mm Hg, 81.77 mm Hg, 85.82 mm Hg for normal, overweight and obese respectively (p<0.001); whereas their systolic blood pressure were 126.85 mm Hg, 132.17 mm Hg, 137.60 mm Hg, respectively (p<0.001).
A limitation of our study was the failure to consider consumption of alcohol and physical activity as independent variables. However, selected variables provided interesting insight into the features of overweight and obesity in Benin. The variables not included in the present study can be catered for in further studies in order to refine the findings.

Conclusion
Overweight and obesity are emerging in Benin, and they are more common in women than men. The independent determinants of overweight and obesity in men and women are aging, formal education, civil servant occupation, and urban residence. Prevention programs are needed to curb the rise of overweight/obesity in Benin.

Competing interests
The authors declare that they have no competing interests.