Abstract

Background

The impact of education on obesity may vary according to population and geographic region. The objective of the present study was to determine the association between education and obesity.

Methods

A cross-sectional study of 3600 subjects aged 20–70 years was conducted by using a cluster sampling technique in an adult population residing in the north of Iran, in 2004. Weight, height, waist and hip circumference were measured and data concerning education level, demographic characteristics and physical activities were collected by interview. Logistic regression analysis was used to estimate the association between education and general obesity (body mass index ≥30) as well as abdominal obesity (waist circumference >88 cm in women and 102 cm in men).

Results

The adjusted odds ratio (OR) for general obesity at education level of high school and college compared with illiterate and primary level was 0.55 [95% confidence interval (CI): 0.43–0.71]. A greater negative association was observed for education at university level (OR = 0.32, 95% CI: 0.22–0.47) irrespective to sex. However, with regard to abdominal obesity, after controlling for confounding factors, the adjusted OR for education at university level remained significant only in women but not in men.

Conclusion

The findings of this study indicate that education level is inversely associated with general obesity in both sexes but with abdominal obesity only in women.

Introduction

Obesity is a well-known risk factor for chronic diseases such as hypertension, heart diseases, diabetes and osteoarthritis. It is associated with an excess mortality rate and a substantial burden of disease.1–5 The prevalence of obesity and overweight is increasing in the USA as well as in other developed and developing countries.6–9 It has already become an epidemic problem and a major public health concern not only in the developed countries but also in the developing countries.6,7,10,11

However, the prevalence of obesity differs according to ethnic and cultural variations across geographic regions, with the Middle East, Central and Eastern Europe and North America having higher prevalence rates.7–9,11–13 There is a relationship between the socioeconomic status (SES) of a country and its prevalence of obesity.12,14–26 In a review of 333 published studies on the association between obesity and SES by McLaren, the overall pattern of results, for both men and women, was of an increasing proportion of positive associations and a decreasing proportion of negative associations as one moved from countries with high levels of socioeconomic development to countries with medium and low levels of development. The results also varied by SES indicator. For women in highly developed countries, negative associations with obesity were most common for education and occupation, whereas positive associations of obesity for women in medium- and low-development countries were most common for income and material possessions.23 The pattern of obesity appears to be different with regard to educational attainment. The relationship between education and obesity has been investigated in several studies.2,12,16–30 In a number of studies, there was a positive relationship between education and obesity.12,20,21,29 However, some studies from industrial countries and in a few developing countries demonstrated that the burden of obesity is shifting toward low-educated and low-SES people.16,20–22,29 Therefore, it is important that each component of SES, in particular the effect of education on obesity is examined separately.

The prevalence of obesity in women is higher than men, and in most countries women show a greater body mass index (BMI) distribution than men.13–16,18 In most studies, there was an inverse relation between education and obesity in women16,20–22,29 whereas in men, there was no association or even a positive association between education and obesity.12,16,20 The impact of different components of SES on obesity is not similar, because each component seems to be exerting different actions in men or women through the influence of other variables.31 This factor may play a role in explaining gender disparities in obesity and even may underlie the racial or ethnic disparities in obesity. The association between education and obesity appears to vary with respect to geographic region and particularly by sex for reasons that are not well understood. Hence, the need is for evidence from different socio-historical contexts. The present study was performed to examine the independent contribution of education to general and abdominal obesity, and whether they differed by sex.

Methods and subjects

Study subjects

The study subjects were recruited as part of our provincial survey of obesity in a population based cross-sectional study in an urban area of the north of Iran. Using a cluster sampling technique, 3600 subjects were selected in four large cities in Mazandran, a province in the North of Iran located to the south of the Caspian sea. From 1 September until 28 December in 2004 a total of 1800 men and 1800 women aged 20–70 years entered the study. These apparently healthy subjects had no known debilitating or systemic diseases, and were living in the geographic regions of the present study. Pregnant women and those on weight loss diets were excluded.

Data collection and measurements

Demographic data such as age, gender, marital status, parental obesity, marriage age, parity, occupation, educational level and also lifestyle data, such as job activity, leisure time physical activity and the number of hours of exercise per week were collected by a trained interviewer using a designed questionnaire. Weight, height, waist and hip circumference were measured using standard methods. Waist circumference (WC) was measured as the diameter at the level of the midpoint between the iliac crest and the lower border of the tenth rib. Hip circumference was measured as the widest circumference around the buttocks below the iliac crest. BMI was calculated as weight in kilogram divided by the square of height in meters (kg/m2).Waist hip ratio (WHR) was defined as WC divided by the hip circumference (cm).

Subjects were classified according to years of education as illiterate (unable to read and write), primary level (<6 years), elementary level (6–8 years), high school and college levels (9–14 years) and university level. We used a standard recommended WHO criterion, as BMI ≥30 kg/m2 to define obesity. WC was considered as a measure of abdominal fat deposition (central obesity). Diagnosis of abdominal obesity in women was based on the values of WC >88 cm, whereas the value of WC >102 cm was considered as abdominal obesity for men. This study was approved by the ethical and research committee of Babol University of Medical Sciences and each participant gave written informed consent prior to their participation in the study.

Statistical analysis

SPSS was used for statistical analysis. In statistical analysis, first we estimated the prevalence of both obesity and abdominal obesity by education level stratified by gender. In logistic regression analysis, four categories of education were used with illiterate subjects and primary (low-educated) level as the reference category. For obesity and abdominal obesity, logistic regression was used to estimate the adjusted odds ratio (OR) with 95% confidence intervals (CI) controlling for several potential confounding factors such as age, gender, marital status, parity, parental obesity, occupational activity and leisure time physical activity and the duration of exercise per week in hours. The interaction of education and sex for both obesity and abdominal obesity was also tested; where there was evidence of different effect of education by sex (i.e. effect modification), sex-specific analysis was also performed. P-value less than 5% was considered as significant.

Results

The mean (±SD) ages of female and male study subjects were 37.5 ± 13.0 years and 38.5 ± 14.3 years, respectively; 83.9% of female and 74.9% of male subjects were married. Education as illiterate and primary, elementary, high school and colleges or university were reported by 31.4, 18.1, 36.4 and 14.1% for women and 18.5, 17.3, 43.2 and 21.0% for men, respectively. In terms of physical activity, 58.7% (65.8% of women and 52.4% of men) had no leisure exercise. However, 5.8% of women and 16.4% of men had exercise activity at the level of 5 h or greater per week. Occupations with low physical activities were reported by 69% of females and 59.6% of males. The distribution of demographic characteristics and physical activities in males and females are presented in Table 1 by education. All characteristics (except parental obesity) were associated with education level in both genders.

Table 1

The distribution of demographic characteristics and physical activities with respect to the educational level in men and women

Characteristics Educational level
 
P-value 
 Illiterate and primary, n (%) Elementary, n (%) High school and college, n (%) University level, n (%) Total, n (%)  
Men 
 Age group (years) 
  20–29 23 (7.0) 97 (32.2) 332 (42.8) 168 (44.6) 620 (34.5) <0.001 
  30–39 38 (11.5) 98 (31.5) 165 (21.2) 90 (23.9) 391 (21.7) 
  40–49 68 (20.5) 66 (21.2) 152 (19.5) 61 (16.2) 347 (19.3) 
  50–59 81 (24.5) 33 (10.6) 96 (12.3) 35 (9.3) 245 (13.6) 
  60–70 121 (36.5) 17 (5.5) 33 (4.2) 23 (6.1) 194 (10.9) 
 Marital status 
  Single 11 (4.6) 59 (19.0) 245 (31.5) 136 (36.1) 451 (25.1) <0.001 
  Married 225 (95.4) 252 (81.0) 533 (68.5) 241 (63.9) 1397 (74.9) 
 Parental obesity 
  Absent 236 (71.1) 200 (64.3) 516 (66.3) 259 (68.7) 1211 (67.4) 0.39 
  Present 96 (28.9) 111 (35.7) 262 (33.7) 118 (31.3) 587 (32.6) 
 Occupational activity 
  Low 179 (53.7) 172 (55.3) 480 (61.7) 241 (63.9) 1072 (59.6) <0.001 
  Moderate 118 (35.4) 122 (39.2) 255 (32.8) 122 (32.4) 617 (34.3) 
  Severe 36 (4.6) 17 (5.5) 43 (5.5) 14 (3.7) 110 (6.1) 
 Exercise, hour/week 
  None 222 (66.8) 175 (56.3) 377 (48.6) 168 (44.6) 942 (52.4) <0.001 
  1–2 67 (20.2) 60 (19.3) 141 (18.2) 83 (22.0) 351 (19.5) 
  3–4 23 (6.9) 40 (12.9) 90 (11.6) 56 (14.9) 209 (11.6) 
  ≥5 20 (6.0) 36 (11.6) 168 (21.6) 70 (18.6) 294 (18.4) 
 Leisure time physical activity 
  Very low 196 (60.5) 176 (56.8) 381 (49.2) 173 (46.2) 926 (51.9) 0.003 
  Low 63 (19.5) 69 (22.3) 21 (27.1) 108 (28.8) 450 (25.2) 
  Moderate 47 (14.5) 47 (5.2) 120 (15.5) 76 (20.3) 290 (16.3) 
  High 18 (5.5) 18 (5.8) 63 (8.1) 18 (4.8) 117 (6.6) 
Women 
 Age group (years) 
  20–29 30 (5.3) 103 (31.6) 301 (46.0) 174 (68.5) 608 (33.8) <0.001 
  30–39 99 (17.5) 114 (35.0) 173 (26.4) 61 (24.0) 447 (24.8) 
  40–49 164 (29.0) 72 (22.1) 122 (18.6) 15 (5.9) 373 (20.7) 
  50–59 170 (30.1) 31 (9.5) 51 (7.8) 2 (0.8) 254 (14.1) 
  60–70 102 (18.0) 6 (1.8) 8 (1.2) 2 (0.8) 118 (6.6) 
 Marital status 
  Single 24 (4.3) 31 (9.5) 122 (18.6) 112 (44.1) 289 (16.1) <0.001 
  Married 541 (95.7) 295 (90.5) 533 (81.4) 142 (55.9) 1511 (83.9) 
 Parental obesity 
  Absent 207 (36.7) 207 (63.5) 382 (58.3) 170 (66.9) 1116 (62.0) 0.03 
  Present 207 (36.7) 119 (36.5) 273 (41.7) 84 (33.1) 683 (38.0) 
 Occupational activity 
  Low 388 (68.7) 208 (63.8) 465 (71.0) 181 (71.3) 1242 (69.0) 0.01 
  Moderate 171 (30.3) 112 (34.3) 182 (27.8) 64 (25.2) 529 (29.4) 
  Severe 6 (1.0) 6 (1.8) 8 (1.2) 9 (3.5) 29 (1.6) 
 Exercise, hour/week 
  None 417 (74.1) 236 (73.3) 186 (28.4) 137 (54.7) 1172 (65.8) <0.001 
  1–2 106 (18.8) 55 (17.1) 305 (46.6) 68 (27.1) 367 (20.6) 
  3–4 22 (3.91) 18 (5.6) 141 (21.6) 27 (10.6) 140 (7.9) 
  ≥5 18 (3.2) 13 (4.0) 22 (3.4) 19 (7.6) 103 (5.8) 
 Leisure time physical activity 
  Very low 384 (67.6) 204 (62.6) 381 (58.2) 132 (52.0) 1101 (61.2) <0.001 
  Low 122 (21.5) 72 (22.1) 173 (26.4) 71 (28.0) 435 (24.2) 
  Moderate 46 (8.1) 41 (12.6) 81 (12.4) 71 (28.0) 211 (11.7) 
  High 16 (2.8) 9 (2.8) 20 (3.1) 43 (16.9) 53 (2.9) 
 Parity 
  None 32 (5.7) 56 (17.2) 186 (28.4) 138 (54.3) 412 (22.9) 0.001 
  1–2 76 (13.5) 129 (39.7) 305 (46.6) 98 (38.6) 608 (33.8) 
  3–4 208 (36.9) 99 (30.5) 141 (21.6) 16 (6.3) 464 (25.8) 
  ≥5 248 (43.9) 41 (12.6) 22 (3.4) 2 (0.8) 313 (17.5) 
Characteristics Educational level
 
P-value 
 Illiterate and primary, n (%) Elementary, n (%) High school and college, n (%) University level, n (%) Total, n (%)  
Men 
 Age group (years) 
  20–29 23 (7.0) 97 (32.2) 332 (42.8) 168 (44.6) 620 (34.5) <0.001 
  30–39 38 (11.5) 98 (31.5) 165 (21.2) 90 (23.9) 391 (21.7) 
  40–49 68 (20.5) 66 (21.2) 152 (19.5) 61 (16.2) 347 (19.3) 
  50–59 81 (24.5) 33 (10.6) 96 (12.3) 35 (9.3) 245 (13.6) 
  60–70 121 (36.5) 17 (5.5) 33 (4.2) 23 (6.1) 194 (10.9) 
 Marital status 
  Single 11 (4.6) 59 (19.0) 245 (31.5) 136 (36.1) 451 (25.1) <0.001 
  Married 225 (95.4) 252 (81.0) 533 (68.5) 241 (63.9) 1397 (74.9) 
 Parental obesity 
  Absent 236 (71.1) 200 (64.3) 516 (66.3) 259 (68.7) 1211 (67.4) 0.39 
  Present 96 (28.9) 111 (35.7) 262 (33.7) 118 (31.3) 587 (32.6) 
 Occupational activity 
  Low 179 (53.7) 172 (55.3) 480 (61.7) 241 (63.9) 1072 (59.6) <0.001 
  Moderate 118 (35.4) 122 (39.2) 255 (32.8) 122 (32.4) 617 (34.3) 
  Severe 36 (4.6) 17 (5.5) 43 (5.5) 14 (3.7) 110 (6.1) 
 Exercise, hour/week 
  None 222 (66.8) 175 (56.3) 377 (48.6) 168 (44.6) 942 (52.4) <0.001 
  1–2 67 (20.2) 60 (19.3) 141 (18.2) 83 (22.0) 351 (19.5) 
  3–4 23 (6.9) 40 (12.9) 90 (11.6) 56 (14.9) 209 (11.6) 
  ≥5 20 (6.0) 36 (11.6) 168 (21.6) 70 (18.6) 294 (18.4) 
 Leisure time physical activity 
  Very low 196 (60.5) 176 (56.8) 381 (49.2) 173 (46.2) 926 (51.9) 0.003 
  Low 63 (19.5) 69 (22.3) 21 (27.1) 108 (28.8) 450 (25.2) 
  Moderate 47 (14.5) 47 (5.2) 120 (15.5) 76 (20.3) 290 (16.3) 
  High 18 (5.5) 18 (5.8) 63 (8.1) 18 (4.8) 117 (6.6) 
Women 
 Age group (years) 
  20–29 30 (5.3) 103 (31.6) 301 (46.0) 174 (68.5) 608 (33.8) <0.001 
  30–39 99 (17.5) 114 (35.0) 173 (26.4) 61 (24.0) 447 (24.8) 
  40–49 164 (29.0) 72 (22.1) 122 (18.6) 15 (5.9) 373 (20.7) 
  50–59 170 (30.1) 31 (9.5) 51 (7.8) 2 (0.8) 254 (14.1) 
  60–70 102 (18.0) 6 (1.8) 8 (1.2) 2 (0.8) 118 (6.6) 
 Marital status 
  Single 24 (4.3) 31 (9.5) 122 (18.6) 112 (44.1) 289 (16.1) <0.001 
  Married 541 (95.7) 295 (90.5) 533 (81.4) 142 (55.9) 1511 (83.9) 
 Parental obesity 
  Absent 207 (36.7) 207 (63.5) 382 (58.3) 170 (66.9) 1116 (62.0) 0.03 
  Present 207 (36.7) 119 (36.5) 273 (41.7) 84 (33.1) 683 (38.0) 
 Occupational activity 
  Low 388 (68.7) 208 (63.8) 465 (71.0) 181 (71.3) 1242 (69.0) 0.01 
  Moderate 171 (30.3) 112 (34.3) 182 (27.8) 64 (25.2) 529 (29.4) 
  Severe 6 (1.0) 6 (1.8) 8 (1.2) 9 (3.5) 29 (1.6) 
 Exercise, hour/week 
  None 417 (74.1) 236 (73.3) 186 (28.4) 137 (54.7) 1172 (65.8) <0.001 
  1–2 106 (18.8) 55 (17.1) 305 (46.6) 68 (27.1) 367 (20.6) 
  3–4 22 (3.91) 18 (5.6) 141 (21.6) 27 (10.6) 140 (7.9) 
  ≥5 18 (3.2) 13 (4.0) 22 (3.4) 19 (7.6) 103 (5.8) 
 Leisure time physical activity 
  Very low 384 (67.6) 204 (62.6) 381 (58.2) 132 (52.0) 1101 (61.2) <0.001 
  Low 122 (21.5) 72 (22.1) 173 (26.4) 71 (28.0) 435 (24.2) 
  Moderate 46 (8.1) 41 (12.6) 81 (12.4) 71 (28.0) 211 (11.7) 
  High 16 (2.8) 9 (2.8) 20 (3.1) 43 (16.9) 53 (2.9) 
 Parity 
  None 32 (5.7) 56 (17.2) 186 (28.4) 138 (54.3) 412 (22.9) 0.001 
  1–2 76 (13.5) 129 (39.7) 305 (46.6) 98 (38.6) 608 (33.8) 
  3–4 208 (36.9) 99 (30.5) 141 (21.6) 16 (6.3) 464 (25.8) 
  ≥5 248 (43.9) 41 (12.6) 22 (3.4) 2 (0.8) 313 (17.5) 

Prevalence rates of obesity, abdominal obesity and the mean of BMI, WC and WHR are summarized in Table 2 by education and sex. The overall prevalence rates of obesity and abdominal obesity were 27.8 and 46.2% for women and 9.9 and 10.6% for men, respectively. The overall mean ± SD of BMI and WC were 26.9 ± 5.4 kg/m2, 87.8 ± 13.6 cm and 25.0 ± 3.9 kg/m2, 89.3 ± 11.5 cm for women and men, respectively.

Table 2

The prevalence of obesity and abdominal obesity and the mean ± SD of BMI, WC and WHR with respect to educational level in men and women

Sex Educational level* Number of subjects Obesity, n (%) Abdominal obesity, n (%) BMI, mean ± SD (kg/m2) WC, mean ± SD (cm) WHR, mean ± SD 
Male Illiterate and primary 333 54 (16.2) 49 (14.7) 25.5 ± 4.4 91.0 ± 12.3 0.92 ± 0.10 
Elementary 310 29 (9.4) 33 (10.6) 27.7 ± 5.5 89.5 ± 1.1 0.90 ± 0.10 
High school and college 777 77 (9.9) 82 (10.6) 25.0 ± 3.9 89.3 ± 11.1 0.88 ± 0.10 
University level 377 18 (4.8) 26 (6.9) 24.4 ± 3.5 87.6 ± 10.8 0.87 ± 0.10 
Total 1798a 178 (9.9) 190 (10.6) 25.0 ± 3.9 89.3 ± 11.5 0.89 ± 0.11 
Female Illiterate and primary 564 234 (41.5) 381 (67.5) 28.9 ± 5.3 94.5 ± 13.5 0.87 ± 0.08 
Elementary 326 106 (32.5) 166 (50.9) 27.7 ± 5.5 88.9 ± 13.8 0.84 ± 0.11 
High school and college 654 134 (20.5) 224 (34.2) 26.0 ± 4.8 84.5 ± 11.9 0.8 1 ± 0.09 
University level 254 25 (9.8) 60 (23.6) 23.8 ± 4.6 80.2 ± 10.8 0.80 ± 0.09 
Total 1798a 499 (27.8) 831 (46.2) 26.9 ± 5.4 87.8 ± 13.6 0.83 ± 0.09 
Sex Educational level* Number of subjects Obesity, n (%) Abdominal obesity, n (%) BMI, mean ± SD (kg/m2) WC, mean ± SD (cm) WHR, mean ± SD 
Male Illiterate and primary 333 54 (16.2) 49 (14.7) 25.5 ± 4.4 91.0 ± 12.3 0.92 ± 0.10 
Elementary 310 29 (9.4) 33 (10.6) 27.7 ± 5.5 89.5 ± 1.1 0.90 ± 0.10 
High school and college 777 77 (9.9) 82 (10.6) 25.0 ± 3.9 89.3 ± 11.1 0.88 ± 0.10 
University level 377 18 (4.8) 26 (6.9) 24.4 ± 3.5 87.6 ± 10.8 0.87 ± 0.10 
Total 1798a 178 (9.9) 190 (10.6) 25.0 ± 3.9 89.3 ± 11.5 0.89 ± 0.11 
Female Illiterate and primary 564 234 (41.5) 381 (67.5) 28.9 ± 5.3 94.5 ± 13.5 0.87 ± 0.08 
Elementary 326 106 (32.5) 166 (50.9) 27.7 ± 5.5 88.9 ± 13.8 0.84 ± 0.11 
High school and college 654 134 (20.5) 224 (34.2) 26.0 ± 4.8 84.5 ± 11.9 0.8 1 ± 0.09 
University level 254 25 (9.8) 60 (23.6) 23.8 ± 4.6 80.2 ± 10.8 0.80 ± 0.09 
Total 1798a 499 (27.8) 831 (46.2) 26.9 ± 5.4 87.8 ± 13.6 0.83 ± 0.09 

*P < 0.001 for overall indexes (BMI, WC, WHR) between male and female.

aTwo of male and two of female subjects had missing data.

The adjusted associations of education with obesity are presented in Table 3. After adjustment for gender, age, parental obesity, marital status, occupational activity, and leisure time physical activity, the duration of exercise per week in hour and parity, the adjusted OR for general obesity for high school and college compared with illiterate and primary was 0.55 (95% CI: 0.43–0.71). A greater negative association was observed for education at university level (OR = 0.32, 95% CI: 0.22–0.47). The association of education with general obesity does not vary by sex (i.e. the interaction was not significant, P = 0.08) whereas, in relation to abdominal obesity, the interaction was statistically significant (P = 0.01).The adjusted associations of education with abdominal obesity and obesity stratified by sex are presented in Table 4. The negative association of education with abdominal obesity was evident in women but not in men.

Table 3

The adjusted OR of educational level on the risk of general obesity with 95% CI for both gender using logistic regression model

Educational level Adjusted ORa (95% CI) 
Illiterate and primary level (ref) 1.0 (—) 
Elementary 0.75 (0.57–0.99) 
High school and college 0.55 (0.43–0.71) 
University level 0.32 (0.22–0.47) 
Educational level Adjusted ORa (95% CI) 
Illiterate and primary level (ref) 1.0 (—) 
Elementary 0.75 (0.57–0.99) 
High school and college 0.55 (0.43–0.71) 
University level 0.32 (0.22–0.47) 

aThe OR was adjusted for age, gender, marital status, parental obesity, occupational activity and leisure time physical activity, the duration of exercise per week in hour and parity.

Table 4

The adjusted OR of educational level on the risk of obesity and abdominal obesity with 95% CI with respect to gender status using logistic regression model

Binary outcome Educational level Male Female 
Adjusted ORa (95% CI) Adjusted ORa (95% CI) 
Obesity Illiterate and primary level(ref) 1.0 (—) 1.0 (—) 
Elementary 0.42 (0.25–0.71) 0.95 (0.68–1.32) 
High school and college 0.46 (0.30–0.72) 0.57 (0.41–0.78) 
University level 0.21 (0.12–0.39) 0.40 (0.24–0.67) 
Abdominal obesity Illiterate and primary level(ref) 1.0 (—) 1.0 (—) 
Elementary 0.88 (0.52–1.48) 0.71 (0.52–0.98) 
High school and college 0.97 (0.62, 1.50) 0.41 (0.31–0.56) 
University level 0.61 (0.53–1.06) 0.35 (0.23, 0.53) 
Binary outcome Educational level Male Female 
Adjusted ORa (95% CI) Adjusted ORa (95% CI) 
Obesity Illiterate and primary level(ref) 1.0 (—) 1.0 (—) 
Elementary 0.42 (0.25–0.71) 0.95 (0.68–1.32) 
High school and college 0.46 (0.30–0.72) 0.57 (0.41–0.78) 
University level 0.21 (0.12–0.39) 0.40 (0.24–0.67) 
Abdominal obesity Illiterate and primary level(ref) 1.0 (—) 1.0 (—) 
Elementary 0.88 (0.52–1.48) 0.71 (0.52–0.98) 
High school and college 0.97 (0.62, 1.50) 0.41 (0.31–0.56) 
University level 0.61 (0.53–1.06) 0.35 (0.23, 0.53) 

aThe OR was adjusted for age, marital status, parental obesity, occupational activity and leisure time physical activity, the duration of exercise per week by hour and parity (for female).

Discussion

Main findings of this study

The present study demonstrated a significant negative association between education and general obesity in men and women, with a clear dose–response from high school to university level compared with illiterate and primary resulted a greater negative association in both sexes. In addition, there was a negative association between education and abdominal obesity only in women but not in men.

What is already known on this topic?

In most previous published studies, there was a negative association of education with general obesity in women, whereas in men there was no association or even a positive association between education and obesity.12,16,20–22,27–30 In previous studies, the association between education and obesity varied according to stage of economic development particularly for men.

What this study adds

In the present study, in contrast to most previous studies, the effect of education on general obesity was similar in both sexes, whereas there was a difference by sex in the association of education with abdominal obesity. Sex different association of education with abdominal obesity as observed in this study was also found in a few previous studies.11,14,20 Our study adds by demonstrating that this difference by sex (in the association of education with obesity) is specific to abdominal obesity in an under-studied developing population.

Several factors should be considered for explaining the effects of education on obesity. People with more education may have healthier lifestyles. Educated people may be more concerned about obesity and have higher awareness regarding the consequences of obesity. They tend to have a healthier diet, characterized by greater consumption of fruit, vegetables and lower fat milk and less consumption of fats23 and may also perform preventive measures better than less educated or illiterate people.

Sex different association of education with obesity may be attributed to different attitudes of women and men toward body weight status and different practices of women and men for controlling body weight.22 There may be more social pressure on highly educated women to be thin than highly educated men and such women may have healthier lifestyles than similar men. A thinner body may be socially valued and materially viable to a greater extent for those highly educated women, for whom thinness continues to be promoted as an ideal of physical beauty.23

Moreover, women with higher education are more likely to engage in preventive health behavior such as regular exercise and better diet compared with their counterparts and may be less likely to have high parity that is associated with overweight and obesity.19 As shown in this study, women at higher education levels were more active than illiterate women both in intensity of occupational and leisure time physical activities as well as in duration of exercise per week. On the other hand, marriage, which is a known risk factor for obesity, was lower among women at university level compared with illiterate women. But the roles of such factors were excluded by regression analysis; however, the contribution role of these factors on obesity and their associations can be partly reduced by changes in lifestyle. In a study from Sweden only 18–29% of the association between educational level and obesity could be explained by the measured lifestyle factors.24 In transition societies income tends to be a risk factor for obesity, whereas education tends to be protective and both gender and level of economic development are relevant modifiers of the influence exerted by these variables.25

Other factors should be also considered to explain sex differences in abdominal obesity. Men are characterized by a preferential accumulation of abdominal adipose tissue and a greater visceral adipose tissue compared with women.32 In a study by Schooling et al.,27 the sex different association of education with metabolic syndrome and WC was attributed to diet-related hormonal changes at puberty which occur first in the more advantaged with economic development. This may outweight the usual protective effect of social advantage in men. In addition, estrogen has been suggested to have favorable impact on postprandial lipemia. So, it may play a sex difference role in abdominal obesity.26 Specific effects of education on general and abdominal obesity in men may also be explained by different associations of occupational and social factors as well as leisure time activities with general obesity and centralization of body fat stores.33

The main strength of the present study is its design, the study population and the sample selection. The sample of this study was drawn from a unique population consisting of subjects with homogenous racial/ethnic characteristics with respect to cultural, socio economic factors or even habitual diet as well as residence areas. Although other factors such as earning capacities of people may affect lifestyle. Nevertheless, homogeneity of several factors in a study population should be considered as a strength of this study. In addition, this study assessed the association of education with obesity taking into account several potential confounders.

Limitations of this study

Our study may have several limitations. First, the cross-sectional nature of this study makes it unable to infer causality, however such analysis, can make an important contribution to the body of evidence about the association of education and obesity. Second, we used WHO criteria but not Asian cutoff values for obesity and abdominal obesity. The characteristics of the study populations in north of Iran are more similar to western populations rather than South Asian population from which the Asian cutoff values were drawn. Third, the data of this study was provided by interview and questionnaire completed by experienced staff. Anthropometric data such as height, weight, WC and WHR were determined by direct measurement but information regarding to physical activities were based on self-reported data. However, self-reported data given by illiterates may not be as valid as from educated participants. Although, we adjusted for the effect of physical activity, the possibility of information bias and residual confounding by physical activities should be considered. Forth, in contrast to some previous studies in which higher and lower educated groups were compared,16,22,28 in this study men and women with different levels of education were compared with illiterate and low-educated men or women. By this categorization, we were able to determine the level of education that can affect obesity. Misclassification of educational might threaten our results. However, this misclassification is probably non-differential so it would not vary with obesity status because the interview was carried out before measuring height, weight and WC. Another limitation of this study was lack of data regarding dietary habits, which may be an important factor concerning obesity and weight gain. In addition, we did not provide data for dietary intake, because the uniformity of diet of this study reduces any confounding effects. On the other hand, in our selection criteria, which recruited apparently healthy subjects by excluding individuals with systemic diseases, the chance of selecting an obese or a low-educated individual may be decreased. Therefore, our exclusion criteria could dilute the negative association of education with obesity. Furthermore, data concerning SES, in particular, data regarding income was not provided in this study, when income is an important risk factor for obesity particularly in men. There is a strong association of SES with both educational attainment and obesity. Thus, the residual confounding may threaten the study results by lack of controlling for income as an important component of SES. However, due to its privacy, self-reported data regarding earnings, usually does not correspond with the real amount of income.

Conclusions

The findings of this study indicate that education has an inverse relation with general and abdominal obesity in women and with general obesity in men. Further studies are needed to explore lifestyle factors that are influenced or modified by education in men or women. Recognizing these factors may facilitate planning of preventive programs for reducing obesity in societies with a high prevalence of obesity-related diseases.

Funding

The data collection of this work was supported by Management, Planning and Budget Council of Mazandaran province (Iran).

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