BMC Public Health 2009, 9:465 http://www.biomedcentral.com/1471-2458/9/465 ates, Table 3 shows that urban overweight/obesity increases with age (p < 0.01), and to a lesser degree, with parity (though women with six or more children were less likely than those with 4-5 children to be overweight or obese). Currently married women were more likely to be overweight or obese than those who had never been mar- ried (p < 0.01). Finally, country differences in the preva- lence of urban overweight/obesity depicted in Figure 1 were apparent in the multivariate results. Malawi had the lowest prevalence (Odds Ratio of 0.79), followed by Burkina Faso (OR of 1.00). At the other end of the scale, Kenya (OR of 1.54) and Niger (1.49) recorded the highest risk of urban overweight/obesity. Interactive model The interaction variables between the variable time lapse, and household wealth and education are displayed in Table 4. The interaction between the variable time lapse and richest household was low and did not reach statisti- cal significance at the level of 10%, indicating that the rate of change in urban overweight/obesity did not signifi- cantly differ between the poor and the richest. Further cal- culations derived from the ORs in Table 3 (not shown) suggest that the rate of increase in overweight/obesity was 3.9% per year among the poorest, and 4.5% per year among the richest but statistically not different. The inter- action between secondary or higher education and time lapse was lower than one and statistically significant, indi- cating that the rate of increase in urban overweight/obes- ity was substantially higher among the non-educated women than their educated counterparts. This result was in line with the descriptive findings. Further calculations (not shown) revealed a rate of increase of 5.4% among the non-educated and only 2.3% among the well educated women. Interaction between country and time lapse is shown in Table 5. Burkina Faso (the reference category), Ghana, Kenya and Tanzania had comparable rate of change over time, while the three remaining countries recorded signif- icantly lower rate of increase in overweight/obesity. Discussion This paper examined changes over time in the prevalence of overweight and obesity among urban adult women in seven sub-Saharan African countries; and investigated the extent to which these changes vary by household wealth and education. Our data for the latest survey showed that on average 31.4% of the women were overweight or obese, with prevalence as high as 38% in Kenya; 35% in Niger and Ghana; and 32% in Tanzania; lower values were observed in Malawi (23%), Burkina and Senegal (28-29%). We speculate that this differential by country could be related to the level of economic development and level of urbanisation, although this is unlikely to be the case with Niger. Our descriptive results on trends over time indicate that overweight/obesity increased by nearly 35.5% between survey 1 and survey 2, as a result of a steep rise in the prev- alence of obesity (+42%) and a smaller increase in over- weight (+14.5%). The multivariate results further showed that the prevalence of overweight/obesity increased by an average of nearly 5% per year. This finding reinforces the observation that obesity is on the increase in urban areas of Africa, and lends support to the WHO warning on an impending dual epidemic of communicable and non- communicable diseases in African in the near future [2]. In line with other studies [6,7,21], our findings showed that women of higher socio-economic status (proxied by household wealth and women's education) were more likely to be overweight or obese than their poorer counter- parts. Similarly women who were engaged in income gen- erating activities (working) were more likely to be overweight or obese. This pattern might be related to changing nutritional and lifestyle trends, with urban pop- Table 4: Odds ratios of ordered logistic regression on the interactions between "Time lapse" and household wealth and education in selected African countries Interaction between Household wealth and Time Interaction between Education and Time lap lap Odds Ratio 95% Confidence Interval Odds Ratio 95% Confidence Interval Time lap (Continuous) Household wealth - Time lap Interaction Middle - Time Richest - Time Education - Time lap Interaction Primary - Time Secondary+ - Time 1.039 ** 1.018 * 1.005 [1.02; 1.05 ] [1.00; 1.04 ] [0.99; 1.02] 1.05 ** 1.00 0.97 ** [1.04; 1.07 ] [0.99; 1.02 ] [0.95; 0.99 ] †p < .10;*p < .05; **p < .01 Note: Estimates for (Overweight or obese) vs Not overweight/obese are the same as for Obese vs (overweight or not overweight/obese) Page 6 of 9 (page number not for citation purposes)