Prevalence of obesity in Iran and its related socio-economic factors

2.1 Study design, subjects and sampling techniques

The MASHAD survey [34] started in 2010 and will continue until 2020. Participants were drawn from three areas in the city of Mashhad (in the North Eastern Iran) using a stratified cluster random sampling method. Each area was divided into 9 locations centered upon Mashhad Healthcare Center divisions. Families were identified initially by finding family members who were within the qualifying age range (35 to 65 years). The local authorities were provided with information brochures and were asked to offer these to qualifying families. Community leaders who were acquainted with the families in the community, helped with the identification and enrollment of potential participants. The demographic, anthropometric and lifestyle figures were collected by two expert health care professionals and a nurse and comprised:

Standard health examination and anthropometric measures: weight, height, BMI, waist-to-hip ratio (WHR), and blood pressure.

2.2 Anthropometric measurements and data collection

Height (centimeters) was documented in all individuals without shoes, and weight (kilograms) was measured using electronic weighing scales with participants wearing light clothing. BMI was calculated using weight in kilograms divided by the square of the height in meters. Waist (at the level of the umbilicus) and hip (defined as the widest part of the body below the waist) measurements were also taken, and the WHR was calculated. WC was determined by measuring waist diameter at the level of the midpoint between iliac crest and lower border of tenth rib. For all the antropometrical parameteres the average of three measurements were used. A current smoker was defined as a person smoking cigarettes at least once a day. An ex-smoker was formerly a daily smoker, but someone who currently did not smoke. A non-smoker was defined as an individual who had never smoked previously.

Obesity was defined using WHO criteria in which a BMI 25–29.9 kg/m² was regarded as overweight; BMI ≥30 kg/m² as obesity [9]. Central obesity was assessed on the basis of WC measurements using cut-off values of WC >88 cm for women and WC >102 cm for men [9].

2.3 Data management

Data collected at the field centers were transferred to the central data bank using Microsoft visual studio. NET software which was used for the overall data management in the MASHAD study. The data were kept consistent with standard operating procedures to maintain subject confidentiality.

2.4 Statistical analysis

SPSS software (version 11.5, Chicago, IL, USA) was used for statistical analysis. Kolomogrov-Smirnov test was used to evaluate the normality of data. Baseline demographics and clinical characteristics were compared between groups using independent samples t-test, chi-square and/or Fisher’s exact test, as appropriate. We used binary logistic regression for determine the association. For all analyses, a p-value ≤0.01 was considered significant.

3.1 Demographic findings

The characteristics of study population who enrolled in the study are shown in Table 1. There were a total of 9775 participants, of whom 40 % were males (n = 3907) and 60 % females (n = 5866). Moreover, overall, 59 (0.6%) were single, 9085 (93.1%) were married, 135 (1.4%) were divorced and 476 (4.9%) were widowed. Among the participants, 303 (7.8%) of men and 1010 (17.4%) of women were illiterate and (17.5%) of men and (8.6%) of women had various levels of university diploma.

Of the male population, 2846 (73.5%) were employed and 696 (18%) were retired. Among the female population, 698 (12.0%) were employed and 247 (4.2%) were retired.

Among our study participants, 57.5% of men and 75.8% of women were non-smokers. Approximately, 28.6% of men and 17.9% of women were current smokers and 13.9% of men and 6.3% of women were ex-smokers.

3.3 Adiposity

The prevalence rates of obesity and overweight are presented in Table 2. The overall prevalence of obesity and overweight were 30.9% and 42.3% respectively. The overall prevalence rate of central obesity by WHO criteria was 46.7% (women 73.3% and men 20.1%). The rate of obesity in women was approximately two and half times greater than for men. The lowest obesity rates in women and men were 8.7% and 4.5% for the 55–65 year age group, and the highest rates were 16.5% and 7.3 % for the 45–54 year age group, respectively. The prevalence of obesity was consistently higher in women compared with men in all age groups. As shown in Table 2, The overall prevalence of obesity and overweight based on distribution of BMI with respected to age, is shown in Table 4, in which the estimated OR (with 95% CI) of obesity are also presented. With respect to results derived from the logistic regression model compared with the group aged 35–44 years, the OR increased to 1.19 and 1.16 for the 45–54 and 55–65 year age groups respectively, and all the results were significant. The age-adjusted OR for female subjects was 3.03 times higher than male subjects (P <  0.0001). There was a statistical significant inverse relationship between the presence of obesity and the levels of educational attainment. Married status was associated with an increased risk of obesity as the adjusted OR increased significantly compare to single status and the risk of obesity increased in married, divorced and widowed status in both men and women (P <  0.0001).

In contrast, there was an inverse relationship between the smoking status and risk of obesity as the risk of obesity decreased in ex-smoker and current smoker respectively (adjusted OR = 0.82, CI: 0.74–0.92, OR = 0.79, CI: 0.67–0.93, P <  0.0001). Similarly there was an inverse relationship between employment status and the risk of obesity; the risk of obesity was higher in those who were unemployed (adjusted OR = 2.36, CI = 0.76–6.96) though the results did not attain statistical significance. The prevalence of obesity fell with increasing physical activity; obesity was reduced by 61% and 65% in subjects with active and very active life-styles, respectively (OR = 0.39, CI = 0.33–0.46 and OR = 0.35, CI = 0.28–0.44). Table 5 shows the prevalence of different degrees of adiposityin relation to the different categories of demographic and lifestyle variables. A χ-square test was used to assess the relationship between degrees of adiposity and various variables (education, gender, employment, marital status and smoking). Thirty eight percent of illiterate persons were overweight and 34% of individuals who were educated to primary school level were obese.

Forty three percent of subjects who had never smoked were overweight and 39% of those who were unemployed were obese. Of those individuals who reported a sedentary life style, 39% and 44.6% of subjects were obese and overweight respectively (p <  0.001). Table 6 shows the prevalence of central obesity with different categories of smoking status; 78.9% of females who were smokers were also centrally obese (P <  0.001) but this relationship was not significant in men.

4.1 Trend in adiposity

Our findings confirm the increase in prevalence of obesity and overweight of about 2.5 fold since the report of a similar study in 2009 [12]. Both obesity and central obesity were more prevalent in women than men with an age adjusted OR of 2.03 and 3.03 for men and female gender respectively. Iranian women may have less physical activity than men because of their limited participation in outdoor activities due to specific climatic and social constraints. With respect to results derived from logistic regression analysis, risk factors for obesity and central obesity were similar. Increasing age, lack of exercise or sedentary lifestyle, unemployed status, residence in urban areas and low levels of educational attainment were the major factors contributing to both obesity and central obesity in women and men in the north east of Iran, which is similar to others reports [12, 13]. The results of the present study are different to the results reported from other geographical areas of Iran. In a study of a representative sample of Tehranian adults, obesity and central obesity were higher in women than in men; 67% vs. 29% for obesity and 93% vs. 74.1% for central obesity, respectively [14] Our result show a lower prevalence of obesity and overweight compared to the latter study. The prevalence of obesity in other parts of the world varies as shown in Table 7. The prevalence of obesity in some countries (Spain, Mexico and Saudi Arabia) is similar to those in Mashhad [15–17]. Mirzazadeh et al. have reported the trend of obesity from 1990–2010 in Iran. They have found that the prevalence of obesity from 1990–2005 increased from 4.3% to 21.3% , but was 14.1% in 2010 [18]. Data from Mashhad shows an increasing trend in obesity and overweight from 2009 [2, 12]. The prevalence of obesity in men and women in the USA reported as 35.5% and 35.8% respectively in 2010. There has been a trend to an increase in the prevalence of obesity in USA since 2002 and it is predicted that the prevalence of obesity, overweight, and extreme obesity will plateau by about 2030 at 28% , 32% , and 9% , respectively [19–21]. Modeled trends from more than 200 countries (1980–2008) indicate steadily increasing prevalence of obesity in every region of the world, including most low and middle income countries, with the steepest increases in higher income countries [22] as exemplified by Iran. Two studies conducted in Mashhad to measure the prevalence of obesity are summarized in Table 8.

Socio-economic status is a complex construct, comprising income, educational attainment, occupation and residential status. This study showed an inverse relation between measures of socio-economic status and obesity that is similar to the results of the study reported in 2009 by Esmaeily. Education may play a role in spreading the awareness about obesity through its impact on knowledge acquisition by individuals about diet, physical activity and their consequences on health status [23]. Similar to other studies [24, 25] the risk of obesity increased with age, with the 45–54 years age group being most at risk of obesity. The frequency of overweight and obesity were found to be higher among individuals who were, or had been, married than among single persons after adjustment for other confounders (OR = 2.39, CI = 1.17–4.87); individuals (particularly men), may have less physical activity, change their dietary pattern, after marriage; these results are similar to those reported by Janghorbani and colleagues [13]. We found that 64.4% and 53.3% of men and women respectively had a sedentary life style and only 14.5% and 20% of men and women respectively were either active or very active. Current smoking rates among men and women were 28.6% and 17.9% , respectively, and this may contribute to the differences in prevalence of obesity and overweight between men and women. A high proportion of the men in this study were smokers, and smoking habit was inversely related to weight, and significantly related to central obesity in women. The inverse association seen between smoking and obesity should not be used to counteract the efforts undertaken against this habit. There is a general belief that smoking may decrease bodyweight by reducing appetite and therefore caloric intake, enhancing metabolism, and reducing fat accumulation [26]. In one previous study weight gain was observed in current smokers as well as ex-smokers and non-smokers, suggesting that the factors promoting weight gain were overcoming the inverse effect of smoking [27].

This current study had several limitations, one of which was that the subjects below 35 years and over 65 years were not included because of financial constraints.