Daily Saliva Osmolarity Feedback May Improve Hydration Status In Recruit Firefighters

Dehydration is a significant issue for firefighters, as reports show that over 90% of firefighters are continually dehydrated. Common factors that lead to dehydration in this population include occupational-related intense physical exertion, hot working environments, and wearing heavy, unbreathable personal protective equipment for long periods. Due to the individual variability in fluid losses, general hydration recommendations may not be sufficient for firefighters to maintain optimal hydration. PURPOSE: To determine if tracking hydration status via saliva osmolarity at the beginning and the end of each work shift for 13 weeks would promote optimal hydration behaviors over time in firefighter recruits. METHODS: Twenty-four firefighter recruits (22 male, 2 female) had hydration status measured via real-time saliva osmolarity testing at the beginning and end of each shift during Fire School for 13 weeks. Average weekly osmolarity scores were analyzed in the morning (AM) and evening (PM). Separate linear mixed-effects models were used to account for missing data scores. Individual participants were specified as a correlated random effect. Averages for each week were computed and designated as the repeated measures fixed factor Week, with 13 points (baseline and weeks 2-13). Bonferroni-adjusted post hoc tests are used when appropriate to identify significant differences between weeks. RESULTS: There was a significant effect of Week on AM [F(12, 204.6) = 3.5, p < 0.001], which was lower in week 12 than in week 4 (Δ = -19.12, p = 0.016) and week 6 (Δ = -18.53, p = 0.026), and which was lower in week 13 than in week 2 (Δ = -18.10, p = 0.035), week 4 (Δ = -19.77, p = 0.010), week 6 (Δ = -19.11, p = 0.017), and week 7 (Δ = -17.95, p = 0.039). There was a significant effect of Week on PM [F(12, 153.2) = 5.2, p < 0.001], which was lower in week 12 than in week 3 (Δ = -18.23, p = 0.019) and week 7 (Δ = -19.88, p = 0.005), and which was lower in week 13 than in week 1 (Δ = -18.04, p = 0.022), week 3 (Δ = -19.79, p = 0.006), and week 7 (Δ = -21.44, p = 0.001). CONCLUSIONS: Hydration assessed by saliva osmolarity improved (decreased) over time in the recruits. This suggests that continual personal hydration status feedback may promote the specific and individualized behavioral changes needed to optimize hydration in this population.