During a panel discussion in Barcelona, Professor Mohammed Gulrez Zariwala, director of the centre for nutritional research at the University of Westminster, Dr Adrian Lopresti, managing director of Clinical Research Australia, and Professor Mark Wetherell, professor of psychobiology at Northumbria University, agreed that sleep be viewed as a central regulator of emotional resilience, cognitive performance and physiological stress response.
Sleep trackers only tell half the story
Prof Zariwala explained that people often oversimplify sleep by relying on metrics like hours slept or wearable tracker scores, assuming these alone reflect sleep quality.
“They look at an activity tracker and conclude ‘I had good sleep’ or ‘I had bad sleep’ or ‘I got seven hours’,” he said. “In reality, sleep is much more complex. There are multiple dimensions: sleep duration, sleep onset, sleep quality, cognition upon waking, and more.”
Prof Zariwala noted that sleep is a foundational pillar of health, strongly linked to mental health, physical disease risk, cognition and longevity. Poor sleep is consistently associated with worse health outcomes across many domains.
“All of these factors need to be considered together, within the broader context of mood, well-being, and cognition, rather than as isolated measures,” he said.
He noted that sleep and mental health have a bidirectional relationship, where poor sleep can contribute to anxiety and depression, while stress and mood disturbances can also disrupt sleep.
“Clinically, it’s important to determine which factors are driving the problem for a particular individual. Is stress and mood disturbance disrupting sleep, or is poor sleep contributing to mood disturbances?” he queried.
Prof Zariwala stressed the importance of a holistic approach in both clinical practice and research, assessing sleep alongside stress, mood, and cognition to fully understand how these systems interact and affect memory, emotional processing and overall cognitive function.
The link between sleep and stress
Dr Lopresti affirmed that sleep and stress are tightly interconnected in a two-way relationship: stress disrupts sleep, and poor sleep increases stress reactivity.
“A colleague’s mildly negative comment may not bother you after a good night’s sleep, but after poor sleep, you’re more likely to perceive it negatively and show a stronger cortisol response,” he noted.
Modern habits like screen use, overstimulation and disrupted light exposure can further worsen sleep by increasing arousal and disrupting circadian rhythms, he added.
“Improving sleep, therefore, requires addressing both stress and lifestyle and environmental factors,” he said.
Poor sleep also affects cognitive processing, with studies showing that sleep-deprived individuals are more likely to interpret neutral facial expressions negatively.
“So if you want to improve sleep, you need to address stress—and if you want to reduce stress, you also need to improve sleep,” he said. “You simply can’t separate the two.”
Cortisol is more than just a stress hormone
Reducing cortisol has become a priority for consumers thanks to the rise of social media wellness trends highlighting cortisol imbalance, with demand growing for solutions that help people feel calmer, sleep better, and recover more effectively.
However, Professor Wetherell noted the conventional interpretation of cortisol as purely a ‘stress hormone’ doesn’t capture its benefits or fit with the true needs of consumers.
“Cortisol is frequently referred to as the stress hormone, but I actually prefer to describe it as an energizing hormone,” he said.
“Yes, cortisol rises during stress because it mobilizes energy and resources. But it also increases during positive experiences.”
He noted that cortisol levels naturally fluctuate throughout the day and in response to a wide range of experiences, not just stress, and that’s why context matters.
“High cortisol isn’t necessarily bad, and low cortisol isn’t necessarily good,” Professor Wetherell said. “We need to understand what the person is experiencing and what demands are being placed on them.”
He noted that this involves considering the cortisol awakening response, explaining that cortisol follows a clear daily rhythm. It rises sharply during the first 30–45 minutes after waking, providing an adaptive boost that helps prepare us for the day. It then gradually declines, reaching its lowest levels before bedtime.
“When viewed as an energizing hormone, this pattern makes perfect sense,” he said, adding “the key is understanding whether cortisol levels are appropriate for the time of day and the individual’s circumstances.”
The future of sleep supplements
The panel noted there is a growing complexity surrounding nutraceutical sleep formulations, as different mechanisms may be required depending on whether the issue is sleep onset, sleep maintenance or non-restorative sleep.
Well-known sleep-supporting ingredients such as magnesium, ashwagandha, saffron, as well as emerging bioactives, act through distinct pathways, including stress modulation, inhibitory neurotransmission and circadian regulation. However, panellists agreed that combination formulations must be carefully validated, as interactions between ingredients may be synergistic or antagonistic depending on dosage and mechanism.
Looking to the future, they said that there is a growing need for more ecologically valid clinical trials that reflect real-world conditions, including workplace stress, screen exposure and irregular sleep schedules.
Furthermore, while much sleep and cognition research has focused on older adults, the panel highlighted emerging evidence that younger populations—particularly university students and young professionals—are experiencing elevated and often overlooked stress burdens.
“There are so many at-risk populations that we know we could do more research for,” said Dr Lopresti.
