Mental stress is among the psychosocial factors thought to contribute to cardiovascular disease (CVD) risk. Heart rate variability (HRV), a measure of the fluctuation in time intervals between consecutive heartbeats, is an important indicator of the cardiovascular system’s response to stress and it is thought that lifestyle factors including physical activity and diet might impact HRV. Higher HRV represents greater adaptability of the heart in response to environmental and psychological challenges, while low HRV is linked to cardiovascular disease and sudden cardiac death.

As part of a recent clinical trial, researchers at King’s College London measured HRV in participants undergoing a mental stress challenge and saw improved measures of HRV in participants who had been replacing typical snacks with almonds over a six-week period. The study was funded by the Almond Board of California.

This new research finding was part of the ATTIS study, a 6-week randomised control, parallel-arm trial, where participants with above average cardiovascular disease risk consumed a daily snack of almonds or a calorie-matched control snack providing 20 per cent of each participants’ estimated daily energy needs. 

In this study, researchers measured participants’ real-time heart rate (HR) and heart rate variability (HRV) at rest (lying down for 5-minute periods) and during a Stroop test (in which participants were asked to read coloured words that is, say ‘red’ in a green font) to simulate short period of mental stress.

During acute mental stress, participants in the almond group showed better heart rate regulation compared to the control group, indicated by statistically significant differences in high frequency power, which specifically evaluates beat-to-beat intervals (a measure of HRV).

Dr Wendy Hall, co-principal investigator (together with Dr Sarah Berry) and reader in nutritional sciences at King’s College London, said, “This study shows that the simple dietary strategy of swapping almonds for typical snacks may bolster resilience to the adverse cardiovascular effects of mental stress by improving regulation of heart rate.  We found that the stress-induced reduction in heart rate variability was lessened in the almond group compared to control following the dietary intervention, which indicates a cardiovascular health benefit. It is useful to think of having a higher HRV as the heart being able to switch gears faster in response to demands on the body, which means more cardiac resilience and flexibility during periods of stress.  In the long term, this is beneficial for cardiovascular health.”