Are social inequities the reason for the increase in chronic non communicable diseases? A systematics review

Chronic non-communicable diseases are a major health concern and have been rising in prevalence over the last decades. These diseases commonly include obesity, diabetes, cardiovascular diseases, dyslipidemia, high blood pressure and asthma and lead to costly complications and diminish the quality of life of those who suffer from them. These diseases, particularly obesity, have traditionally been associated with socioeconomic privileges; nevertheless, recent studies have associated non-communicable diseases (NCDs) with disadvantaged conditions such as food insecurity, low income, poverty, inadequate living conditions and unemployment.1 Eighty percent of the deaths caused by NCDs have been reported to occur in low and middle income countries and have been responsible for 44% of deaths globally. Combined with infectious diseases (including HIV, tuberculosis and malaria), poor maternal and perinatal conditions and nutritional deficits, these diseases double the death rate1 and will have important economic losses. Over the next 10years, China, India and the United Kingdom will lose close to $558billion, $237billion and $33billion, respectively, as a result of cardiovascular diseases, stroke and diabetes. These loses will be partly due to the reduced economic activity caused by occupational absenteeism induced by NCDs complications.

obesity and co-morbidities of obesity, are increasing in low income populations.
In addition, the so-called Nutrition Transition phenomenon describes body composition alterations due to changes in lifestyle patterns as a consequence of urbanization and migration. This process is occurring at different levels around the world, but is particularly high in low and middle income countries where gaps in the quality of life might be wide among different population groups. 6,7 In addition to the previous statements, it should be noted that NCDs can be prevented with cost-effective measures, particularly those associated with lifestyle changes. Obesity and type 2 diabetes (T2DM) are two diseases whose complications can include high blood pressure, dyslipidemia and cardiovascular diseases. Specially for those in poverty, risk factors for diseases start early in life, even in utero and they face a lifecycle of disadvantageous conditions. An undernourished pregnant mother is at risk of having a premature or low birth weight baby, predisposing the baby to cardiovascular diseases later in life. 8 Frequently occurring in low income settings, pregnancy during adolescence has also shown risks for intergenerational malnutrition consequences such as low height, increased adiposity and early onset of T2DM among others. 9 A concern for health practitioners that should also be a concern for policy makers is that a large portion of the population still lives in inadequate conditions. A systematic review of the indexed literature was conducted to clarify these aspects within the context of policymaking.

Methods
A systematic search for peer-reviewed information was conducted between March 15 and June 12, 2013 focusing in the association between social inequities and the presence of non-communicable diseases with strong emphasis in Latin America, but not excluding other countries if they were found during the search. We searched in four databases: (3 of which are from Latin America) Latin American Archives of Nutrition database (ALAN), Scielo, Lilacs and Science Direct for published indexed literature between January 2000 and May 2013 using the following terms in Spanish, Portuguese and English: "social inequities", "social disparities", "food security/insecurity", "poverty", "nutrition transition", "non-communicable diseases (NCDs)", "obesity", "hypertension", "diabetes" and "asthma".
The inclusion and exclusion criteria were as follows: original articles published during the established period that showed the association between social inequities expressed as food insecurity, poverty, low income, low socioeconomic status, disadvantaged living conditions and the presence and/or risk of the following noncommunicable diseases: obesity, diabetes, hypertension, dyslipidemia, cardiovascular diseases and asthma. Studies included were those in which the unit of analysis was individuals, including children, adolescents and/or adults, or specific groups of households or schools.
Letters to the editor, commentaries or perspectives were excluded, as well as books and grey literature.
The eligibility of the articles was initially ascertained by screening the titles in order to exclude non-relevant studies and remove duplicates of articles identified in multiple databases.
Two investigators (KM and MAC) independently reviewed the studies for eligibility according to the criteria above. Any differences were agreed upon by all authors.

Data extraction and reporting
Because of the relatively novel topic, the team agreed on the above inclusion/exclusion criteria. Traditionally, poverty and its associated social inequities have been related to communicable diseases and poor nutrition, and this phenomenon still exists. The team decided to include any of the manifestations of social inequities, as they express the vulnerable group's opportunity for exposure to disparities. As a result, analyses of food insecurity, poverty, low socioeconomic status and belonging to a particular ethnic group were included so that different aspects of the life experience in disadvantaged conditions could be approached as determinants of chronic non-communicable diseases. A large emphasis was made on articles on Latin America because of the authors research interests were compatible with this region's characteristics and the authors are involved in regional projects, whereby understanding social inequities as an influence of developing NCDs would be important. However, articles that fit the inclusion criteria and examined other countries were included because of the topic's relevance and to learn different approaches.
After searching the four databases, 395 total articles were found; 36, 21, 290 and 48 were found from ALAN, Scielo, Science Direct and Lilacs, respectively. After matching and discarding the duplicates and non-relevant articles for the selected topic, 22 total articles were included in this systematic review as shown in Figure 1.

Categorization of results
Articles were categorized by their bibliographic characteristics according to the following criteria: number of authors, year of publication, language of publication, country of origin and center or academic institution to which authors are affiliated and the database from which they were obtained ( Table 1). The articles were also categorized according to subjects/units of analysis, methodology and findings (

Results
Of the twenty two retrieved articles, all highlighted the association between social inequities including poverty, food insecurity and other social disadvantaged statuses and different nutritional diagnoses or medical entities. Of these, eight articles were related to obesity and eight were related to cardiovascular disease risk or alterations including hypertension. In addition, one article studied asthma, one examined metabolic syndrome and four were related to growth impairments including low stature (Table 2).

Studies showing a relationship between a sociodemographic variable and obesity and metabolic syndrome
From these studies, five, showed a trend toward developing obesity with the presence of poverty, food insecurity or living in disadvantaged conditions, while the remaining three showed a trend toward the rise of obesity when socio-economic status is higher. The Peruvian articles showed good examples of differences in results across the same age groups within the same country. For instance, the Health and Familiar surveys (Endes) reported a trend toward the increased risk of becoming obese in extreme poverty strata 15 while Pajuelo et al. 13 reported a higher prevalence of obesity in higher socioeconomic statuses. Cardenas et al. 18 reported that metabolic syndrome was related to older ages in Peru and decreased while poverty was accentuated. Bustos et al. 11 found a relationship between belonging to an ethnic (indigenous) group and a higher risk of becoming obese and stunted but found less risk of becoming obese when living in poverty as a member of a non-indigenous group.

Studies showing associations with cardiovascular diseases
In particular, the association with cardiovascular diseases and at least one of the manifestations of social inequities such as low level of education or lack of schooling appears to be an influencing factor in the presence of cardiovascular disease and mortality as a consequence of these entities. In addition, diabetes appears to be higher amongst groups with low education levels. In contrast, Morenoff et al., 21 reported no consistent evidence that social inequities affected the treatment of hypertension in the Chicago area, while Addor et al., 23 found that a social gradient affected the increase in cardiovascular risk in low educated girls and women in a Swiss study. Carneiro et al., 19 in Brazil found a significant association between mortality due to CVD and living with low SES.  Obesity was higher in boys (10,6%) and weight deficit was higher in girls (5,3%). Stunting was higher in boys (25,3%) These outcomes were associated with extreme poverty in the community

Studies showing associations with growth impairments in children
Studies reporting growth alterations essentially focus on stunting. Van de Poel et al., 29 reported a large gap between rural and urban children and highlighted that urban poor children are at risk of stunting. In addition, Molina 28 reported that growth alterations occurred in a low income community in Peru in which obesity is as low as 0.9% of the studied population, while 22.4% reported growth retardation and 1.8% was severely stunted. Navarrete et al., 31 reported that obesity was higher in Chilean boys between 2-5years of age (10.6%) compared with girls (5.3%); 25.3% of the boys showed stunting and these outcomes were associated with extreme poverty.

Study showing associations with asthma
An association was reported between asthma and poor housing conditions, low per capita income and low birth weight in a study by Benicio et al. 27

Discussion
The rise in the prevalence of non-communicable diseases worldwide is a serious issue, particularly in the developing world where good life conditions might not reach a large proportion of individuals. How social inequities are associated with the appearance of NCDs is a complex question to answer. Globalization and demographic transition and urbanization processes had been keys to generating economic development. On the one hand, these processes have made interesting improvements in health achievements but have contributed to rise of social disparities on the other hand. 32 Uncontrolled access to unhealthy foods and the fact that some groups who previously did not have consistent access to food now can regularly access cheap and calorie-dense food have been determinants in the rising prevalence of overweight and obesity in disadvantaged groups. 5 As evidenced in the majority of the articles above, an association between social inequities and the presence of non-communicable diseases, particularly between obesity, increased cardiovascular risks, diabetes and altered growth pattern in children has emerged as an interesting topic for research. The traditionally expected outcome for those living in poverty is changing from undernourishment and classic stunting to the coexistence of obesity and excess weight and stunting and low weight, as shown in several studies, highlighting the presence of "the double burden of malnutrition". 6 Interestingly, when analyzing the studies, differences within the same country could be observed. In one community, characteristics of low income, poverty and social inequities and the consequences of over nutrition status and NCDs can result in an increase in the prevalence of obesity, while the same sociodemographic characteristics in other communities can manifest as marked undernourishment. 13,15,28 This should be taken cautiously when analyzing social determinants of NCD since characteristics of the communities themselves can influence particularly the nutritional outcomes, rather than an absolute criteria of the association of poverty and being socially disadvantaged and the presence of overweight and obesity this show the multidimensionality of social factors and their complex interactions.
In addition, a gap between the rural and urban population was observed, resulting in different perspectives for analysis and interpretation. This gap is evident in children's nutritional status, as observed in Mexico City where children attending 6 schools were 2.53 more likely to be obese if living in food insecure households than their food secure counterparts. 14 By contrast, in a more rural, small city (Chalhuanca, Peru), a sample of children had an obesity prevalence of 0.9% and 22.4% had stunted growth. 28 Wasting in children, manifesting as low weight for height, is caused mainly by immediate caloric deficiencies and has been associated traditionally with food insecurity and hunger. On the other hand, stunting or chronic malnutrition happens when consistent low levels of insufficient caloric intake are present and are also associated with micronutrient deficiencies. 33 Wasted children are susceptible to disease while stunting reduces later performance at school and income as adults. Moreover, stunting starting early in life increases the risk of obesity and NCDs later in life, which is a key motivation of this present article. 34 As a result, these differences might mean that access to opportunities is unevenly distributed among the population and that the nutrition and demographic processes are at different levels of evolution in different regions. Additionally, as was shown in an important quantity of the articles in this review, low education level is a key factor, particularly nutritional knowledge. While not specifically addressed in these articles, lack of nutritional knowledge is as an obstacle to achieving good health and preventing the presence and evolution of NCDs when improved outcomes such as obesity are ameliorated. 35 Equally important is the types of disadvantages these communities are experiencing. Thus, programs and interventions cannot be the same for a totally deprived community compared with a low income community.
There are several definitions and categorizations of poverty, including differences in approaches according to the elements taken into account. The one introduced by Walter 36 is an interesting one, as it describes a classification in external poverty characterized by low income and difficulties for maintenance and internal poverty that would include potentially harmful effects on good and adequate nutrition. The latter concept would refer to knowledge and beliefs about nutrition and attitudes as a key factor of good eating habits that are even more important than income. A recent study found no relationship between income and obesity in a disadvantaged population. However, when considering the line of poverty, the association was statistically significant, also low level of education was a factor that increased the risk of being obese, which is important when considering the multidimensionality of poverty for analysis. 37 The aspects that are to be considered when assuming the different aspects of poverty are more complex than just lack of adequate income. In spite of being important elements for quality of life, low education, lack of nutritional knowledge and family structure are aspects that will impact nutritional adequacy and ultimately the development of a chronic condition related to nutritional disease. 4,38 The formula to explain the increasing prevalence of noncommunicable diseases is complex and it reflects cultural, geographical, genetic and other differences. NCD as shown can express in affluent communities as well as in disadvantaged ones. However, inequality in access to goods and services is a constant; in a changing world, understanding that malnutrition and obesity can be expressions of inequalities in access to food and education requires a methodological effort. It is not logical to think that less food results in more malnutrition and that more food results less malnutrition. The nutrition transition phenomenon does not appear to be a continuum from the weight-height deficit towards obesity through normal status. Rather, it seems that the two poles of malnutrition and obesity are on one side of the spectrum and normal on the other and determining the factors for non-communicable diseases.