Effect of Black Pepper & Rosemary on Attention, Motivation, Mental Energy & Fatigue

Lindheimer JB, Loy BD, O'Connor PJ

Objective

The objective of this experiment was to test whether the consumption of a single, practical amount of black pepper or rosemary impacts feelings of mental energy and fatigue, perceived motivation to perform cognitive tasks, or performance on a cognitive task that required sustained attention.

Methods

Forty young adults with below average feelings of energy were given capsules containing either black pepper [2.0 g], rosemary [1.7 g], or a placebo [3.1 g rice flour]. Outcomes were measured before and twice after they orally consumed capsules [after a 1 hour rest period to allow treatments to become bioavailable]. Sustained attention was measured using a 16-min dual task, in which, single-digit numbers were presented every second on a screen and the participant performed both a primary task [detection of three successive, different odd digits] and a secondary task [detection of the number 6]. Feelings of energy and fatigue were measured using the vigor and fatigue subscales of the Profile of Mood States and visual analog scales (VAS).

Results

Analysis of variance showed non-significant condition [spice versus placebo] x time [T1, T2, & T3] effects for motivation, measured with a VAS, and the intensity of energy and fatigue feelings. Unadjusted effect sizes revealed that rosemary induced small, transient reductions in false alarm errors (d = 0.21) and mental fatigue (d = 0.40) at isolated time periods. Time-varying analysis of covariance, controlling for motivation to perform cognitive tasks, showed no significant effects on the primary or secondary task outcomes of correct responses [hits], errors [false alarms, misses], speed of response [reaction time], and signal detection sensitivity.

Conclusion

It was concluded that black pepper and rosemary, consumed in a capsule form, in the doses used and while wearing a nose clip to block olfactory effects, do not induce consistent short-term improvements in sustained attention, motivation to perform cognitive tasks, or feelings of mental energy and fatigue in young adults with low energy.