Physiological Response and Adaptation to Heat Stress Among Florida Agricultural Workers in Hot and Cool Environments Open Access

Krishna, Tara (2016)

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PURPOSE: Relationships between climate and health are of particular interest in the context of projected global temperature changes. A growing body of literature calls for the study of heat-related illnesses (HRI) in outdoor agricultural workers, whose jobs regularly involve strenuous activities in hot conditions.The aims of this study were to (1) compare physiological heat stress responses between Florida agricultural workers in hot and cool environments and (2) characterize differences in workers' use of adaptive strategies (clothing and fluid choices) to address heat stress in hot and cool conditions.

METHODS: Data were collected from 11 Florida fernery workers in winter and summer of 2015. In both seasons, participants wore heart rate monitors during three workdays and swallowed thermometers that tracked core temperatures for the same period. Participants answered questions about clothing and fluid choices. Paired t-tests and McNemar's tests were used to compare data by season. Clustered Cox regression was used to compare, by season, the time participants took to reach the Occupational Safety and Health Administration heat stress risk threshold (core temperature of 38°C) on each workday.

RESULTS: Physiological heat stress responses--as measured by average maximum core body temperatures and heart rates--did not differ by season (all p>0.05). The hazard of reaching the heat stress threshold also did not differ in the summer [HR 1.1 (95% CI 0.3-3.3)] compared to the winter. All participants reached the threshold at some point in the study, and equal numbers (9) of participants reached it in both seasons. Only work hours and reported use of wide-brimmed hats differed. In winter, participants reported working longer hours [8.2 (SD 1.5) vs. 6.0 (SD 1.0); p<0.01]. In summer, participants more often reported wearing wide-brimmed hats (p=0.02).

CONCLUSION: This study is the first to quantify and compare agricultural workers' physiological heat stress responses, and--despite its small sample size--its results reveal a nuanced relationship between climate and health. Although environmental temperatures in the winter and summer portions of this study were significantly different, participants' heat stress responses were largely the same; thus, vulnerability to HRI is determined by more than just high temperatures.

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