The cumulative effect of coffee and a mental stress task on heart rate, blood pressure, and mental alertness is similar in caffeine-naïve and caffeine-habituated females

Most North American workers drink coffee throughout their workday, although the cumulative effect of job stress and coffee is not well known. Research has shown that coffee affects the cardiovascular system and mental alertness primarily through the active ingredient caffeine; however, the dose of caffeine used in these studies is greater than a normal cup of coffee. In addition, these changes have been mostly determined in male caffeine-habituated consumers. Therefore, this study examined the effect of a normal cup of coffee on the cardiovascular and mental alertness response both before and after a mental stress task in 10 caffeine-naïve (23 ± 5.0 years) and 10 caffeine-habituated (25 ± 6 years) females. Blood pressure, heart rate, and mental alertness were taken at baseline (before coffee), 50 minutes after finishing coffee and immediately after a 9-minute mental stress task. The volume of coffee ingested for a 15-minute period was 350 mL (12 oz), which is equivalent to 140 mg of caffeine. The combined effect of coffee and mental stress significantly decreased diastolic blood pressure (Δ8 mm Hg) and increased heart rate (Δ6 beats per minute) and mental alertness (Δ67.3%) in caffeine-naïve and caffeine-habituated females, whereas systolic blood pressure (Δ10.3 mm Hg) only increased in the caffeine-naïve participants. Our results indicate that a normal cup of coffee can effect changes in blood pressure and mental alertness and that mental stress may alter the magnitude of change; however, the transient increase in systolic blood pressure after drinking coffee in caffeine-naïve participants requires further investigation.