Caffeine Intake Influences The Blood Pressure Response To Strenuous Physical Exertion Among Firefighters

Abstract

Caffeine may diminish the immediate blood pressure (BP) reductions that occur after an exercise bout, termed post-exercise hypotension (PEH). Neither PEH nor the influence of caffeine on PEH have been studied in firefighters (FF), who have a disproportionate high risk of sudden cardiac death on the job, partially due to its strenuous nature and poor nutrition. PURPOSE: To examine the influence of caffeine intake (CAF) on PEH after a maximal graded exercise stress test (GEST) in FF. METHODS: FF (n=15) completed a non-exercise control (CONTROL) and GEST in random order on separate non-work days. They left the laboratory attached to an ambulatory BP (ABP) monitor for 19hr. CAF was assessed with the National Health and Nutrition Examination Survey food-frequency questionnaire. Repeated measures ANCOVA in SAS tested if the ABP response after GEST vs CONTROL differed by CAF group divided by the median as high (806.8+190.7mg) and low (239.3+202.9mg) with baseline ABP as a covariate. RESULTS: FF were overweight (29.0+3.9kg/m2), middle-aged (40.2+9.5yr) men with elevated resting BP (124.1+10.3/79.6+11.5mmHg). CAF tended to be positively correlated with resting SBP (r=.50, p=.06) and DBP (r=.50, p=.06). Among the total sample, the systolic ABP (ASBP) (18.0+4.8mmHg, p<.01) and diastolic ABP (ADBP) (9.1+1.5mmHg, p<.01) changes from baseline were greater after GEST vs CONTROL over 19hr, independent of CAF (Ps>0.05), but with significant interactions among ASBP, ADBP, and CAF over 19hr (Ps<0.05). These interactions revealed ASBP was consistently greater after GEST vs CONTROL over 19hr in high CAF (p<=0.01 GEST vs CONTROL); whereas in low CAF the difference in ASBP after GEST vs CONTROL was variable over 19hr (p=0.03 GEST vs CONTROL x Time). By contrast, the ADBP response after GEST vs CONTROL over 19hr tended to be greater in low (15.3+4.5mmHg, p=.08) than high CAF (4.4+2.4mmHg, p=.05). DISCUSSION: This small sample of FF exhibited post-exercise hypertension and CAF seemed to modulate this adverse response. Further study is needed in a larger sample of FF to confirm our findings and better establish the relationship of these associations. Supported by the University of Connecticut Institute for Collaboration on Health Intervention and Policy and the United States Department of Agriculture (SAES, HATCH Project No. CONS00954).