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A groundbreaking study has revealed that heat stress may have a significant impact on infant growth, both during pregnancy and up to the age of two. The research, published in The Lancet Planetary Health, is the first of its kind to demonstrate the adverse effects of high temperatures on infant development post-birth. The study, conducted by researchers from the Medical Research Council Unit The Gambia (MRCG) at the London School of Hygiene & Tropical Medicine (LSHTM), adds to previous findings on how heat stress impacts fetal development.
Key Findings
The analysis, based on data from a clinical trial in The Gambia, discovered that a 1°C rise in average daily heat stress during the first trimester of pregnancy corresponded to a small reduction in birth weight for gestational age. Interestingly, the second trimester showed no significant effects from heat stress, while in the third trimester, a possible increase in head circumference relative to body size was observed, though this finding is less certain.
The study also found that infants exposed to high heat after birth, up to the age of two, were more likely to have lower weights and heights compared to their peers. The most pronounced decreases were noted in infants aged 6 to 18 months, particularly in those who had experienced higher average daily heat stress in the three months prior. For instance, 12-month-old infants exposed to average heat stress of 30°C were found to have reduced weight for height and age, in comparison to those exposed to 25°C.
The research involved 668 infants—329 females and 339 males—and assessed the effects of heat stress on growth parameters such as weight, length, and head circumference for gestational age, and on weight and height during the first two years of life.
Public Health Implications
The study’s authors emphasize the urgent need for public health interventions to address the increasing risks posed by climate change, particularly for vulnerable populations such as pregnant women and infants. Dr. Ana Bonell, Assistant Professor at MRCG and the lead author of the study, highlighted the intersection of climate change, food insecurity, and undernutrition, which disproportionately affects young children in regions like West Africa.
“These findings build on previous evidence showing that the first trimester is a vulnerable time for heat exposure. It’s crucial to understand the factors contributing to these outcomes, such as heat stress affecting appetite, food intake, and possibly cellular and inflammatory pathways,” said Dr. Bonell.
The data analyzed in this study was collected during the Early Nutrition and Immunity Development (ENID) randomized controlled trial, conducted in West Kiang, The Gambia, from 2010 to 2015. The researchers used the Universal Thermal Climate Index to define heat stress, considering factors such as heat, humidity, wind speed, and solar radiation. The average heat stress exposure level during the study was 29.6°C, with daily maximums reaching up to 45.7°C.
Call for Global Action
As global temperatures continue to rise, the researchers stress that these findings should serve as a wake-up call for urgent action. With child wasting rates remaining alarmingly high and ongoing planetary warming, targeted interventions are needed to mitigate the health risks faced by children in regions most vulnerable to heat stress.
Further research is needed to explore the relationship between heat stress and growth in other regions beyond The Gambia. The study’s limitations include the lack of data on dietary habits, maternal infections, and socioeconomic factors, all of which could influence growth outcomes.
Nonetheless, the study is a critical step forward in understanding how climate change impacts child health and growth, providing essential insights for developing public health strategies in the face of global warming.
Reference: Effect of heat stress in the first 1000 days of life on fetal and infant growth: a secondary analysis of the ENID randomised controlled trial, The Lancet Planetary Health (2024).
