Abstract
Irrespective of their genetic makeup, children living in an ideal home environment that supports healthy growth have similar growth potential. However, whether this potential is true for children residing at higher altitudes remains unknown. To investigate whether altitude is associated with increased risk of linear growth faltering and evaluate the implications associated with the use of the 2006 World Health Organization growth standards, which have not been validated for populations residing 1500 m above sea level. Analysis of 133 nationally representative demographic and health cross-sectional surveys administered in 59 low- and middle-income countries using local polynomial and multivariate regression was conducted. A total of 964 299 height records from 96 552 clusters at altitudes ranging from -372 to 5951 m above sea level were included. Demographic and Health Surveys were conducted between 1992 and 2018. Residence at higher altitudes, above and below 1500 m above sea level, and in ideal home environments (eg, access to safe water, sanitation, and health care). The primary outcome was child linear growth deficits expressed in length-for-age/height-for-age z scores (HAZ). Associations between altitude and height among all children and those residing in ideal home environments were assessed. Child growth trajectories above and below 1500 m above sea level were compared and the altitude-mediated height deficits were estimated using multivariable linear regression. In 2010, a total of 842 million people in the global population (approximately 12%) lived 1500 m above sea level or higher, with 67% in Asia and Africa. Eleven percent of the sample was children who resided 1500 m above sea level or higher. These children were born at shorter length and remained on a lower growth trajectory than children residing in areas less than 1500 m above sea level. The negative association between altitude and HAZ was approximately linear through most part of the altitude distribution, indicating no clear threshold for an abrupt decrease in HAZ. A 1000-m above sea level increase in altitude was associated with a 0.163-unit (95% CI, -0.205 to -0.120 units) decrease in HAZ after adjusting for common risk factors using multivariable linear regressions. The HAZ distribution of children residing in ideal home environments was similar to the 2006 World Health Organization HAZ distribution, but only up to 500 m above sea level. The findings of this study suggest that residing at a higher altitude may be associated with child growth slowing even for children living in ideal home environments. Interventions addressing altitude-mediated growth restrictions during pregnancy and early childhood should be identified and implemented.
Highlights
Local polynomial regressions between age and height-for-age z scores (HAZ) indicated that growth faltering for both altitude groups occurred during the first 24 months (Figure 1)
Do the findings of this study indicate that the 2006 World Health Organization (WHO) growth standards should be adjusted downward for children residing 1500 m or more above sea level? Such adjustments would imply that altitude-mediated growth deficits are just physiologic adaptations and are not linked to more serious functional deficits
While this might be the case for a small proportion of the population that has resided in highaltitude areas over multiple generations to benefit from genetic adaptation,[39] for most of the population, the growth impairments imply more serious functional deficits related to intrauterine growth restriction and impaired cognitive development.[40,41,42]
Summary
While researchers have used different definitions for high altitude,[16] we used the 1500 m above sea level threshold because sites located above this altitude were not considered eligible in the Multicentre Growth Reference Study. We compared child growth trajectories at lower than 1500 m above sea level and 1500 m or more above sea level altitudes using local polynomial regression methods. Previous literature has attributed high-altitude growth deficits to poorer nutrition, health, and socioeconomic conditions at high-altitude localities.[13,17] Considering these issues, we accounted for the role of confounding factors in 3 ways. We used linear regression methods to quantify the child height deficit associated with altitude after adjusting for confounding factors. We used the same multivariable regression models to assess how altitude is associated with immediate causes of malnutrition: 978 JAMA Pediatrics October 2020 Volume 174, Number 10 (Reprinted) jamapediatrics.com
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