Conducted between 2011 and 2017 by a team from the Department of Psychological Medicine and Department of Biochemistry at the university’s Yong Loo Lin School of Medicine, the study surveyed over 600 Singaporean Chinese seniors above 60 years old.
The researchers conducted the study — published in the Journal of Alzheimer’s Disease — with support from NUS’ Life Sciences Institute and Mind Science Centre, as well as the Ministry of Health’s National Medical Research Council.
In it, they reported that seniors over the age of 60 who ate more than two ‘standard’ portions of mushrooms a week could lower their risk of mild cognitive impairment (MCI).
The researchers defined a single portion as a ¾ cup of cooked mushrooms, weighing approximately 150g on average, and added that even one portion a week could still help to reduce MCI risk.
This effect of mushroom intake was attributed to a single common ingredient found in the six types of mushrooms referenced in the study: golden, oyster, shiitake, white button, dried, and canned.
The ingredient, known as ergothioneine (ET), is said to be a unique antioxidant with anti-inflammatory properties that cannot be synthesised by the human body but can be obtained from dietary sources such as mushrooms.
This finding is consistent with a previous study by the same team, which assessed elderly Singaporeans and found that the plasma levels of ET in those with MCI were markedly lower than healthy seniors of similar age.
This led them to hypothesise that ET deficiency could be a risk factor for neurodegeneration, and that increased ET intake through food could support cognitive health.
Dr Irwin Cheah, senior research fellow at the Department of Biochemistry, told NutraIngredients-Asia: “Due to its high oxygen consumption, the brain is very prone to oxidative stress. Numerous studies have shown that ET is able to scavenge certain reactive oxygen species (ROS) and may possibly protect the brain from oxidative damage.
“We (and other groups) have demonstrated that ET may protect against beta-amyloid, a peptide implicated in Alzheimer’s disease, by preventing oligomer formation. Other groups have also shown that ET can protect neurons in a range of in vitro and in vivo models.
“Mushrooms contain a myriad other compounds as well, and these may also be beneficial in slowing or preventing cognitive decline, but for now, our research is focused on ET.”
In addition to ET, other compounds found in mushrooms were said to possibly aid in lowering MCI risk. These included certain hericenones, erinacines, scabronines and dictyophorines that might promote the synthesis of nerve growth factors.
Furthermore, bioactive compounds in mushrooms may also prevent neurodegeneration by inhibiting the production of beta-amyloid and phosphorylated tau, as well as acetylcholinesterase.
In terms of whether or not there were significant differences between the different mushroom types used in the study when it came to preventing or slowing MCI, Cheah said: “We did not investigate the effects on MCI between the different types of mushrooms, as the samples sizes were too small.
“There are differences in the levels of ET between the different types of mushrooms, but it should be noted that most mushrooms contain much higher levels of ET compared to other foods, so in general, most mushrooms can be said to be beneficial.”
The researchers also made it a point to determine MCI in the participants. MCI is considered the stage between regular cognitive decline in ageing and more severe decline, such as in dementia.
Common signs of MCI are memory loss and forgetfulness, as well as compromised cognitive function in areas such as attention, language, and visuospatial abilities.
These changes are often subtle, and seniors with MCI do not usually experience disabling cognitive deficits that affect their day-to-day activities, something Alzheimer’s disease and other dementia patients typically experience.
As such, the researchers sought to determine if the study participants performed worse on standard neuropsychologist tests than their peers of a similar education level.
They conducted extensive interviews with and tests that took into account demographic details, medical history, psychological factors and dietary habits. A nurse then measured their blood pressure, weight, height, handgrip strength, and walking speed before performing a screen test on anxiety, cognition and depression.
A two-hour standard neuropsychological assessment with dementia rating followed, and the overall test results were discussed comprehensively with qualified psychiatrists before arriving at a diagnostic consensus.
Spore to come
In addition to lowering MCI risk, mushroom consumption was found to benefit those already experiencing MCI, with earlier research supporting this conclusion.
Assistant professor Feng Lei, from the Department of Psychological Medicine, said: “A small trial from Japan reported improvement in cognition among individuals with MCI after consuming mushroom dry powders for 16 weeks.”
Spurred by these positive findings, the research team is considering conducting an RCT using a pure ET compound and other plant-based ingredients, such as L-theanine and catechins from tea leaves, to determine if these phytonutrients can prevent cognitive decline, or delay it in subjects with MCI.
Feng said, “We are planning a study on the cognitive benefits of a new formulation of nutraceutical or supplement. We plan to combine several phytonutrients based on findings from this study and many other studies we have conducted in the past decade.
“We will focus on older adults with early signs of cognitive decline and those who carry APOE e4, a genetic risk factor for Alzheimer’s disease. However, this study is still in the planning stages, so I cannot share any more details at this moment.”
Further into the future, Feng and his team will also be looking to pinpoint other dietary factors that may be linked to healthy brain ageing and a lowered risk of age-related conditions.