Effect of oral contraceptive consumption timing on substrate metabolism, cognition, and exercise performance in females: a randomised controlled trial

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Abstract The pharmacokinetic profile of oral contraceptives (OCs) results in an acute, transient increase in circulating synthetic reproductive hormones. The aim of this study was to examine the effects of acute OC ingestion on cognitive function, substrate metabolism and exercise performance. Sixteen combined OC (30µg ethinyl oestradiol and 150mg Levonorgestrel) users ingested either their OC or placebo (PLA) in a randomised, double-blind, crossover manner. After 60 minutes, participants completed tests of verbal memory and verbal fluency, followed by sub-maximal treadmill exercise for 6 minutes at 60% lactate threshold (LT) and 90% LT where respiratory exchange ratio (RER), carbohydrate oxidation, fat oxidation, heart rate (HR), rating of perceived exertion (RPE), felt arousal and feeling scale were recorded. Participants then completed an incremental ramp test to exhaustion to assess time to exhaustion (TTE) and peak oxygen uptake (VO 2 peak), before ingesting the pill corresponding to the condition, they were not in. RER, arousal and feeling scale were all significantly lower in the OC condition compared to PLA (all P < 0.05) with no difference in HR, carbohydrate oxidation, fat oxidation, RPE, TTE or VO 2 peak (all P > 0.05). Verbal fluency score was significantly higher in the OC condition compared to PLA (P < 0.05), with no differences between conditions for any aspect of verbal memory (all P < 0.05). Combined OC ingestion acutely affects substrate metabolism, affective responses to exercise and verbal fluency. The timing of OC ingestion should be considered in relation to aspects of physiological function. Key findings Ingestion of a combined oral contraceptive (OC) results in a transient increase in circulating synthetic reproductive hormones. The altered reproductive hormone profile affects substrate metabolism and affective responses to exercise. Cognitive performance in a verbal fluency task is also improved post OC ingestion. The within-day timing of OC ingestion can be manipulated to affect aspects of physiology, which may have implications for athletes, exercises and the general population, in addition to interpretation of prior research using OCs.

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