Health inequalities are evident in a rural district of Kerala, with Scheduled Tribe members bearing a higher burden of morbidity compared to non-tribe groups. However, not all indigenous groups are equally disadvantaged. The largest tribal group, the Paniya, have higher unmet health needs compared to other Scheduled Tribes in this area, specifically with respect to underweight, anaemia and goitre. Comparison of morbidity across age groups reveals that this social gradient of inequality is apparent across generations. In contrast to levels observed in older adults, higher hypertension levels among young Paniya adults compared to their peers in other social groups point to a greater double burden of disease in this subgroup. Although tribal groups have higher levels of poverty, stratifying morbidity by household economic status does not change the gradient observed.
Strengths and limitations of study
This is the first study in Kerala, to our knowledge, to explore the extent of social inequalities in health between indigenous and non-indigenous people based on multiple clinical markers of morbidity. This allows us to quantify the vulnerability of indigenous groups across the spectrum of deteriorating health and disease, both in terms of morbidity resulting from the classical conditions of deprivation associated with poverty (anaemia, goitre, undernutrition and tuberculosis) and that associated with the epidemiologic transition (hypertension as a marker of cardiovascular risk). The limitations of our study lie first of all in the capacity to explore in greater depth how each disease process evolved. A more systematic study of each morbidity type would require biological and clinical investigations that go beyond the current population survey approach and objectives of the study. Secondly, none of the indicators assessed are able to reflect the situation unequivocally. Genetic differences between ethnic groups contribute to differences in attained adult height that may bias the validity of BMI <18.5 kg/m
2 as a measure of underweight in this area; however, models including only adults with a height over 150 cm provided similar results. Anaemia was measured using clinical indicators associated with severe anaemia and may be more prevalent among the Paniya than other groups for genetic reasons, such as a higher prevalence of sickle cell disease [
39,
40]. Nutritional deficiencies are not the only causative factor of goitre. Different survival rates across groups may have also moderated the gaps observed, given the lower life expectancy for the Paniyas and other Scheduled Tribes. Nonetheless the convergence of results and consistency of the patterns observed are reassuring and support the central hypothesis about the vulnerability of indigenous people, in particular the Paniyas.
Comparison with other studies
Heightened vulnerability of Scheduled Tribes to underweight [
41,
42] and anaemia [
6] has been shown in other studies at a national level. While the risk of underweight was associated with lower socioeconomic status in those studies and ours, the odds of being underweight were still nearly twice as high for tribe compared to non-tribe members in our study, independent of their household poverty status. Furthermore, despite the widespread improvement in education and other social determinants of health and nutrition, there is no evidence in our sample of a reduction in underweight prevalence among younger adults from any social group. This is consistent with findings from a study comparing underweight in Indian adults between national surveys in 1998–99 and 2005–06 [
41]. During this period of time, underweight prevalence in women decreased by only three percentage points and no age-related changes in underweight prevalence were observed.
Despite the epidemiological transition taking place in Kerala State [
43,
44] and the potential for heightened sensitivity to lifestyle-related chronic disease risk factors as a result of childhood undernutrition [
45,
46], no major shift in disease burden was observed in our sample. Hypertension prevalence estimates in rural areas of India ranged from 10% to 20% in earlier studies [
47], similar to the levels found in this study, but have been as high as 42% in a more recent study in Kerala [
43]. The higher hypertension levels observed among young Paniya adults suggests a higher level of vulnerability to post-transition diseases in these adults at the lower rung of society, although we did not assess in this study the potential contribution of genetic factors. Stress or psychosocial adversity in these individuals may contribute to this vulnerability, as younger Paniya members have not experienced improved life and work opportunities, despite benefiting from increased education opportunities [
16]. Chronic stress associated with social position has biological effects that may contribute specifically to social gradients in risk of coronary disease and other morbidity [
48]. Psychosocial factors also directly affect health related behaviours such as smoking, diet, alcohol consumption and physical activity, which also play an important role in blood pressure regulation [
49]. Further research into the specific factors contributing to hypertension in this subgroup is needed.
Overall, the accumulation of health deficits in the Paniya group is indicative of their heightened vulnerability in terms of high exposure to health risks and barriers to accessing health care [
50]. It is also consistent with the Paniyas’ own perceptions as voiced in focus group discussions, in which numerous vulnerability traps related to a range of risk factors were identified, including poor health, landlessness, poverty, exposure to harsh environmental conditions (e.g. floods), alcohol use, colony isolation, and education deficits [
25,
51]. The consistency between our survey findings and the views of the Paniyas themselves increases our confidence in the robustness of the results.
Although caste-related differences in Kerala may be lower than in other parts of India, the results of our study suggest that this social determinant still underlies overall inequality [
52]. By disaggregating the analyses by groups that mirror the social caste hierarchy, we observed a consistent health gradient across these groups. Individuals with Forward Caste affiliations are in better health compared to Other Backward Classes, who in turn are in better health than Scheduled Tribes, with Paniyas having the poorest health. A similar gradient in risk factors for ill health across the four groups was also observed (data not shown). An earlier study among women in this area also showed inequalities across caste groups in women’s perceived health, measured by self-reported health and limitations in daily activity [
53].
Excluding the case of anaemia, roughly half of the health gap between tribes and non-tribes remains unexplained by differences in endowments. Our results correspond with those of Das [
36] and Borooah [
54] on the inequalities of poverty in India. In their respective studies, the authors found that the greater part of the difference in poverty rates between Scheduled Tribes and the general population was attributable to differences in coefficients rather than endowments; a result seen as “a likely indication of discrimination” [
36]. In a recent study aimed at decomposing malnutrition inequalities in India, Van de Poel and Speybroeck [
55] found that more than one-third of the malnutrition gap was attributable to differences in the effects of health determinants after controlling for a large set of explanatory variables.
Can the observed health gradient be explained solely by the concentration of poverty among tribal groups? Our results suggest not and are in contrast to others that suggest caste is diminishing in its importance in determining social status and associated health inequalities in India [
56]. A recent study on mortality showed mixed results, with evidence for attenuation of caste differences when adjusted for living standards in the working age group (19–64 y) but a strong influence of caste in younger age groups, even after controlling for standard of living [
3]. In our study of adults, the health gradient between social groups was still evident among those of similar economic status, indicating that health inequalities are rooted in social structures much deeper than material deprivation. The Blinder Oaxaca decomposition supports this position; differences in the effects of health determinants appear to play an important role. The unexplained part of the health gap reflects differences in the processes that generate health outcomes across social groups. It is likely that a significant part of this gap is driven by discriminatory practices and differential rates of returns on endowments for tribal and non tribal populations, especially since differences in endowments between indigenous and non-indigenous groups (poverty status, occupation, education, housing conditions, etc.) are themselves largely attributable to past exclusion and discrimination practices [
36].