Stunting

Stunting indicates a failure to achieve one’s genetic potential for growth (Dewey & Begum, 2010) and reflects the outcome of frequent or extended periods of ill health and poor nutrition, particularly during the first two years of life (Bhutta & Salam, 2012). Studies of affluent households across a wide variety of ethnic backgrounds and cultural settings have indicated growth potential in preschool children to be highly similar across countries (Bhandari, Bahl, Taneja, de Onis, & Bhan, 2002; WHO Multicentre Growth Reference Study Group & de Onis, 2006). Chronic restriction of growth may arise from multiple factors, including recurrent infections and poor nutrition in the antenatal, intrauterine and postnatal periods (de Onis, Blossner, & Borghi, 2012; Grantham-McGregor et al., 2007). Children measuring more than two standard deviations below internationally-accepted growth standards are considered stunted, and those measuring more than three standard deviations below are severely stunted (WHO Multicentre Growth Reference Study Group, 2006).

Although the short-term mortality risk is less than that associated with wasting, the implications of stunting extend well into adulthood (Figure 1). Analysis of cohort studies from five LMIC has identified child stunting to be correlated with diminished cognitive and physical development, reduced educational attainment and physical work capacity, lower earning potential and an increased risk of chronic disease, such as obesity, diabetes or cardiovascular disease, in adulthood (Adair et al., 2013; Black et al., 2013; Martorell et al., 2010; Victora et al., 2008). The multiple dimensions of the cost of stunting to society include increased health care expenses, reduced earnings, and losses to national economic productivity (Shekar, Dayton Eberwein, & Kakietek, 2016).

Figure 1. Proposed causes and consequences of undernutrition throughout the life cycle, highlighting the potential for genetic and environmental influences to have intergenerational effects (ACC/SCN, 2000).

Analysis of 39 nationally-representative datasets from LMIC in 2001 indicated the mean length-for-age at the time of birth to be very close to the formerly-used National Center for Health Statistics growth reference (Hamill, Drizd, Johnson, Reed, & Roche, 1977), with growth faltering beginning immediately after birth and continuing well into the third year (Shrimpton et al., 2001). Similar analyses comparing anthropometric surveys against the current World Health Organization (WHO) child growth standards (WHO Multicentre Growth Reference Study Group, 2006) show an even more dramatic faltering of length-for-age from birth until 24 months of age, emphasising the importance of the window of opportunity of the first two years of life to prevent long-term effects of undernutrition (Victora, de Onis, Hallal, Blössner, & Shrimpton, 2010).

A review of interventions targeting child undernutrition, including the promotion of improved breastfeeding and complementary feeding practices, micronutrient interventions, and general supportive strategies to improve household nutrition and reduce rates of infectious disease, suggest that these strategies are only able to reduce stunting at 36 months of age by around one-third (36%) (Bhutta et al., 2008). To eliminate stunting in the longer-term, there is a need to address the underlying determinants of undernutrition, such as poverty, limited formal education, disease burden and gender inequity, which may contribute to intergenerational effects (Ramakrishnan, Martorell, Schroeder, & Flores, 1999; Stein et al., 2004). Analysis of nationally-representative data from Bangladesh and India revealed both maternal and paternal education to be strong determinants of child stunting, and attributed a 4-5% decrease in the likelihood of stunting to each additional year of formal education for mothers (Semba et al., 2008).

Stunting levels in Tanzania

The United Republic of Tanzania is the fifth most populous country in sub-Saharan Africa, with a projected population of 51.6 million in 2017 (NBS Tanzania & OCGS, 2013). Strong and consistent economic growth has been recorded since around 2000, yet this has not translated into a significant reduction in poverty (Arndt, Demery, McKay, & Tarp, 2016; Atkinson & Lugo, 2010) and the country ranks at 96 of 118 countries on the Global Hunger Index, based on levels of undernourishment, child wasting, child stunting and child mortality (von Grebmer et al., 2016). Across sub-Saharan Africa, the prevalence of stunting has been reported to have remained stable at around 40% between 1990 and 2010, in contrast to a dramatic decrease from almost 49% to less than 28% in Asia over the same time period (de Onis et al., 2012). High levels of population growth in sub-Saharan Africa have translated into an increase in the number of stunted children, from 45 million in 1990 to 60 million in 2010.

Tanzanian data compiled from five consecutive applications of the Demographic and Health Survey (DHS) show a reduction in the national prevalence of stunting from 43.4% to 34.4%, and of severe stunting from 17.8% to 11.7%, between 1996 and 2015-16 (Figure 2). Higher levels of stunting are consistently reported amongst children living in rural areas compared to those in urban settings. Research in Central and Eastern Africa has attributed this pattern to differences in wealth between rural and urban households (Kennedy, Nantel, Brouwer, & Kok, 2006).

Studies in Kenya and Zambia have also demonstrated poor child health outcomes, including levels of stunting, morbidity and mortality, in urban unplanned settlements or slums (Fotso,

Ezeh, Madise, & Ciera, 2007; Fotso et al., 2012; Zulu et al., 2011). In Tanzania, a higher incidence of stunting has also been associated with poor maternal nutritional status, low levels of maternal education and lower household wealth (MoHCDGEC [Tanzania Mainland], MoH [Zanzibar], NBS Tanzania, OCGS, & ICF, 2016).

Substantial regional variation exists in the prevalence of stunting across the country. This has been attributed to the differing agro-ecological conditions, which influence the types of foods consumed and the timing of its availability, access and utilisation throughout the year (Lobell, Schlenker, & Costa-Roberts, 2011). Communities participating in the research project contributing to this thesis are located in Singida Region, in an area adjacent to the border with Dodoma Region. Stunting levels in Dodoma Region have consistently been recorded as being higher than in Singida (Figure 3), and were reported as the highest nationally in 2010, at 56.0%

(NBS Tanzania & ICF Macro, 2011). Dodoma is characterised by a prevalence of highly food-insecure areas, with a reliance on rain-fed agriculture and a food system based predominantly on cereals (Mbwana, Kinabo, Lambert, & Biesalski, 2017), although with regular use of a wide range of non-cultivated fruits and vegetables (Mutabazi, 2013).

The communities participating in this study are located close to the border between Singida and Dodoma Regions. Based on common food systems and agro-ecological conditions in this area, the likelihood of study participants accessing markets and health facilities in both regions and the reported disparity in regional health statistics, nutritional figures for both Singida and Dodoma Regions are reviewed here.

Figure 2. National prevalence of (a) stunting (HAZ <-2) and (b) severe stunting (HAZ <-3) in children under five years of age, overall and disaggregated by location of residence, compiled from Tanzanian Demographic and Health Survey data (1996 to 2015-16).

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Figure 3. Prevalence of (a) stunting and (b) severe stunting in children under five years of age, at a national level and within Singida and Dodoma Regions, compiled from Tanzanian Demographic and Health Survey data (1996 to 2015-16).