A new study released this week by Ethiopian researchers shows that children who are born at higher altitudes, such as 1,500m (4,921 ft) above sea level, are more at risk of being smaller at birth and have a stunted growth compared to their counterparts born at lower altitudes. The research is published in the latest issue of the journal JAMA Pediatrics.
Study premise and highlights
The question which the researchers attempted to answer in this study was if there was an effect of being born at high altitudes on linear growth patterns of children. This large study of over 900,000 children aged from birth to 5 years (59 months) showed that those born at higher altitudes had a lower growth trajectory compared to children born and living at lower altitudes. The team found that this “altitude-mediated growth difference” was significant even when they adjusted for other factors such as ideal home environments for the children.
What was done?
The team of researchers wrote that it is known that genetically different children living in an ideal home environment that promotes healthy growth have similar growth potential. This study attempted to see if altitude could affect growth even when the children grew up in ideal home environments. They wanted to evaluate the implications associated with the use of the 2006 World Health Organization growth standards. These standards, they wrote were not tested upon communities and populations living 1500m above sea level.
For this study, the team included 133 cross-sectional surveys conducted across the nation representing a varied population. Data was gathered from 59 countries, and a total of 964,299 records of heights were gathered from 96,552 clusters of data. The populations studied lived in altitudes ranging from − 372 to 5951 m above sea level. The survey was conducted between 1992 and 2018.
An ideal home environment was defined as “access to safe water, sanitation, and health care.” Higher altitudes were defined as those above 1,500m above sea level. The researchers measured “child linear growth deficits” measured in terms of “length-for-age/height-for-age z scores (HAZ).” An association between HAZ and altitude was looked at for all children that lived in ideal home environments. A comparison of growth trajectories was made between children living above and below 1,500 m above sea level, and statistical tests such as multivariable linear regression were used to assess the “altitude-mediated height deficits.”
What was found?
Some of the key findings from this large study were as follows;
- Around 12 percent of the world population, translating into around 842 million lived 1,500m above sea level or higher in 2010. Study co-author Kalle Hirvonen, a senior research fellow at the International Food Policy Research Institute, in a statement said, “More than 800 million people live at 1,500 meters above sea level or higher, with two-thirds of them in Sub-Saharan Africa, and Asia.” Even in the United States, several cities are above 5,000 feet over sea level, they said. Some of these include Butte, Cheyenne, Jackson, Laramie, Flagstaff, Arizona, Las Vegas, Albuquerque Santa Fe, Mammoth Lake, Big Bear Lake, South Lake Tahoe and 37 cities in Colorado. Aspen, Breckenridge, and Telluride, for example, are over 7,000 feet over sea level.
- Most of the individuals residing at altitudes 1,500m above sea level or higher were from Asia or Africa (67 percent)
- Of all the children surveyed in this study from birth to 59 months of age, 11 percent lived in 1,500m above sea level or higher.
- The growth trajectory of children born in higher altitudes was significantly lower than those residing in lower altitudes.
- There was a negative linear association between altitude and HAZ.
- For a 1,000m over the sea level rise in altitude, there was a “0.163-unit (95% CI, −0.205 to −0.120 units) decrease in HAZ”, the team wrote.
- Among children living in ideal home environments, the HAZ numbers were as predicted by the 2006 World Health Organization HAZ distribution. This was however, true for altitudes up to 500m above sea level only. Beyond that, the association did not work.
The researchers concluded that those children born and living in higher altitudes, even in ideal home environments, might be growing slower than children residing at lower altitudes. They wrote, “Interventions addressing altitude-mediated growth restrictions during pregnancy and early childhood should be identified and implemented.” They added that there should be special attention and guidance should be provided for pregnancies and their management in high altitude settings. They did not however, recommend changes in the 2006 World Health Organization growth standards specific to altitude.
Hirvonen explained, “Pregnancies at high-altitudes are characterized by chronic hypoxia, or an inadequate supply of oxygen, which is consistently associated with a higher risk of fetal growth restriction.” Babies born at high altitudes thus suffer from lack of oxygen at birth. Hirvonen said they had expected that inheriting genes from ancestors living for generations at high altitudes could mitigate the effects of altitude. The reality was different.
Study author Kaleab Baye director of the Center for Food Science and Nutrition in Addis Ababa, Ethiopia added in a statement, “A first step is to unravel the complex relationship linking altitude, hypoxia, and fetal growth to identify effective interventions.” Hirvonen said, “If children living at altitude are, on average, more stunted than their peers at sea level, then a more significant effort to address high altitude stunting is needed.”