Age-related Gastrointestinal And Inflammatory Responses When Performing Consecutive Days Of Moderate-intensity Work In The Heat

To safeguard worker health and safety, regulatory agencies recommend that workplaces implement heat mitigation controls in the form of work-rest allocations to limit elevations in core temperature (i.e., ≥1 °C above rest). However, current recommendations do not consider next-day impairments in heat dissipation which augment physiological strain on the following day in older but not young adults. Older adults also exhibit age-related increases in enterocyte damage following acute exercise in the heat. However, it is unclear whether older adults experience greater gastrointestinal disturbance and downstream inflammatory responses when performing consecutive days of prolonged work in hot conditions. PURPOSE: To assess markers of enterocyte damage and immune activation in young and older adults performing work in the heat over consecutive days. METHODS: Ten young (mean [SD]: 22 [2] years; 5 female) and 10 older (62 [5] years; 5 female) adults performed moderate-intensity treadmill walking (metabolic heat production of ~200 W/m2) in wet bulb globe temperatures of 26 °C until core (rectal) temperature reached 1 °C above rest. Thereafter, they completed the 240-min work bout consisting of 45 min work bouts followed by 15 min rest breaks. The protocol was repeated in the afternoon (following a 1-h lunch break) and next morning. Plasma markers of enterocyte damage (LBP) and immune activation (sCD14) were assessed at baseline and the end of each work bout using ELISAs. Data were analyzed via a two-way ANOVA, with Fisher’s LSD (α = 0.05). RESULTS: In parallel to elevated core temperature, LBP was increased from baseline in both groups after each work bout (main effect: p = 0.02), although responses did not differ between groups (p = 0.77). While sCD14 was elevated after each work bout on day 1 in older adults (bout 1: +2874 pg/mL [4]; bout 2: +4975 pg/mL [1463]; both, p ≤ 0.02), elevations were sustained after performing work the following morning (bout 3: +4975 pg/mL [1463]) (all, p < 0.001). sCD14 was greater in older compared to young adults for all bouts (all, p < 0.01). CONCLUSIONS: We observed signs of enterocyte damage in young and older adults following work in the heat over consecutive days. However, older adults may experience greater immune activation and therefore inflammatory responses than their younger counterparts. Supported by: Workplace Safety Insurance Board (Ontario)