Written by: Sandeep Ravindran, Ph.D. | Issue # 86 | 2019
- Stress influences cognitive performance, and phospholipids have been shown to reduce certain stress responses.
- A new study investigated the stress-buffering effects of milk-based phospholipids on cognitive performance and response to stress.
- The study found that dietary intake of phospholipids from cow milk improved reaction time on certain tasks among perfectionist men.
Stress affects us in many ways, including well-studied impacts on cognition [1,2]. “We know stress, in certain situations, can negatively impact some domains of cognitive performance,” says Dr. Neil Boyle from the University of Leeds.
A new study by Boyle and his colleagues examined whether intake of certain kinds of fats, known as phospholipids, might protect against the detrimental effects of stress on cognitive performance . Phospholipids play important structural and functional roles in our brain and nervous system, and phospholipids from cow and soy milk have been shown to have stress-buffering effects [4-8].
“The interest stemmed from early evidence of the capacity of phospholipids to mediate the cortisol response to stress and exercise,” says Boyle. In humans, cortisol is a primary moderator of the acute effects of stress on cognitive function [9,10]. Stress often affects cognitive performance only when it significantly elevates cortisol levels [11,12].
“Therefore, we were interested to see if phospholipids could reduce the cortisol response to induced stress and subsequently offer some protective effects on cognitive performance undertaken under the context of the stressor,” says Boyle. “A psychosocial stressor was used as this type of stressor is the most activating of the cortisol stress response, and it is also the type of stressor commonly experienced in everyday life,” he says.
The researchers decided to examine the effects of phospholipid supplementation on the cognitive performance of individuals that were particularly vulnerable to stress, and focused on a population of “perfectionist” men. Perfectionism—which includes excessive standards, self-criticism, and a need for order—has been associated with an increased fear of failure and an increased responsivity to cortisol [13,14].
“We selected perfectionists as the negative effects of stress and cortisol on cognitive performance are often seen in individuals that demonstrate the highest cortisol response to stress provocation,” says Boyle. “Perfectionist tendencies have previously been associated with this tendency to high cortisol responsiveness,” he says.
Designing appropriate experiments to accurately assess the effects of phospholipids was a challenge. “Changes in cognitive performance as a result of dietary interventions tend to be quite small and can therefore be lost or washed out by differences between individuals,” says Boyle. “Therefore, it is often beneficial to examine changes in performance after an intervention within the same person,” he says.
But traditional laboratory experiments of stress usually result in a habituation of the participants’ cortisol responses with repeat exposure to stress. “We spent a lot of time modifying existing stressors to reduce habituation in response so we could examine cognitive performance after a stressor before and after phospholipid intake in the same individuals,” says Boyle.
The researchers examined the effects of six weeks of daily intake of either a drink containing cow milk-derived phospholipids or a placebo drink that did not contain phospholipids on 54 perfectionist men. They measured the participants’ stress responses to an acute psychosocial stressor, and also their subsequent cognitive performance.
The researchers found that phospholipid intake improved post-stress reaction time performance on an attention-switching task, in which participants had to rapidly switch between multiple tasks. Supplementation with phospholipid did not significantly reduce salivary cortisol responses to stress. “We did not demonstrate an effect on cortisol response, but an effect on subjective arousal rating and a small impact upon reaction time,” says Boyle.
Working memory performance was unaffected by phospholipid supplementation, suggesting that the benefits of phospholipid intake may be specific to certain cognitive domains. Phospholipid intake also increased subjective levels of energy and arousal during peak stress exposure, which may have increased participants’ stress-coping potential. The researchers suggest that subjective stress-buffering effects of phospholipid intake may explain the improved cognitive performance in the absence of attenuated cortisol response.
“The findings were not sufficient in isolation to make dietary recommendations, which would require replication and more numerous and larger studies,” says Boyle. “However, the small reaction time effects found may be suggestive of some benefit in contexts in which small performance improvements are beneficial,” he says.
Future studies will be needed to better understand the mechanisms by which phospholipids affect cortisol responses to stress. Larger follow-up studies could also look at the effects of phospholipids in specific populations.
“I suspect any positive effects of phospholipids are more likely to be evidenced in samples that are more commonly vulnerable to cognitive deficits or the negative effects of stress,” says Boyle. “For example, an intervention aimed at protecting or improving cognitive performance may be more likely to have an effect in an elderly sample compared to a young sample,” he says.
Phospholipids may also be particularly helpful in the context of sports. “I consider sports performance, particularly sports endurance, as relevant future areas of research,” says Boyle. “Early evidence suggests phospholipids may offer performance and recovery improvements in this context,” he says.
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