Natural compounds found in apples can reduce the risk of developing Alzheimer’s and other forms of dementia, scientists say.
High concentrations of compounds in apples and other plants, known as phytonutrients, stimulate the creation of neurons, in a process called neurogenesis.
Neurons are highly excitable cell that transmits information to parts of the body via electrical signals – and they boost our learning and memory abilities.
Two compounds – quercetin in apple peel and dihydroxybezoic acid (DHBA) in apple flesh – generated neurons in the brains of mice in lab tests.
Interestingly, apple juice was not found to significantly contribute to neurogenesis, suggesting the benefits apply to eating the whole apple and not just a glass of juice.
The crunchy fruits are a popular staple and have health benefits which can keep you out of the doctor’s office – or so the saying goes
The research was led by experts from the German Centre for Neurodegenerative Diseases (DZNE) in Bonn, Germany.
‘An apple a day keeps the doctor away – there may be some truth to this aphorism,’ they say in their paper, published in Stem Cell Reports.
‘In this study we demonstrate that apples contain pro-neurogenic compounds in both their peel and their flesh.’
The study showed that lab-grown stem cells from adult mouse brains generated more neurons and were protected from cell death when quercetin or DHBA were added to the cultures.
Two compounds – quercetin in apple peel and dihydroxybezoic acid (DHBA) in apple flesh – generated neurons in the brains of mice in lab tests
WHAT ARE PHYTONUTRIENTS?
The term phytonutrients is a broad name for a wide variety of compounds produced by plants.
They’re found in fruits, vegetables, beans, grains, and other plants.
Each phytonutrient comes from a variety of different plant sources and has different effects on the body.
Some researchers estimate there are up to 4,000 phytonutrients.
Scientists have identified thousands of them, although only a small fraction of phytonutrients have been studied closely.
Many phytonutrients have antioxidant properties that help prevent damage to cells throughout the body.
A number of phytonutrients have been shown to reduce the risk of cancer, heart disease, stroke, Alzheimer’s and Parkinson’s disease.
Source: UnlockFood/Produce for Better Health Foundation
Subsequent tests in mice showed that in distinct structures of the adult brain associated with learning and memory, stem cells multiplied and generated more neurons when the mice were given high doses of quercetin or DHBA.
The effects on neurogenesis were comparable to effects seen after physical exercise, which is a known stimulus for neurogenesis.
This suggested natural compounds in fruits, not just quercetin and DHBA but potentially others, may act in synergy to promote neurogenesis and brain function when given in high concentrations.
Given the wide consumption of apple juice, researchers also examined whether consumption of whole apple juice concentrate affected neurogenesis in the lab mice.
To eliminate any possible effect of the increased caloric intake of fruit sugar, a group of mice received a portion of sugar water with equal calories, as well as a control group that received normal drinking water.
Three weeks after being given apple juice, mice were trained to locate a submerged escape platform in a circular pool, known as the Morris water maze task.
This was designed to detect the contribution of adult-generated neurons to the overall performance in spatial navigation and cognitive flexibility.
However, apple juice supplementation was found to have no effect on adult neurogenesis or learning.
‘Given that the quercetin concentration in apple juice is very low (below 2 mg/litre) … we conclude that this is likely an insufficient concentration of active phytochemical to modulate neurogenesis,’ the team say.
Researchers did point out that a 2010 study showed the consumption of apple juice improved behavioural symptoms in human patients with Alzheimer’s.
Future studies will be required to determine if quercetin, DHBA and other phytonutrients can enhance learning and cognitive function in humans.
Flavonoids, the abundant phytonutrients found in fruits and vegetables, can modulate molecular signalling pathways that influence cognitive abilities.
Dietary flavonoids are naturally occurring in fruit, vegetables, chocolate, and beverages like red wine and tea.
Although it’s known an apple a day keeps the doctor away, two daily apples might be better to reduce the risk of suffering a heart attack or stroke, experts found in 2019.
When 40 people with slightly high cholesterol ate two large apples a day for eight weeks, it lowered their levels of ‘bad’ cholesterol by almost four per cent.
Two apples a day could help to reduce their risk of a stroke or heart attack, which can be caused by cholesterol hardening the arteries.
‘It seems the old adage of an apple day was nearly right,’ said study author Professor Julie Lovegrove, from the Hugh Sinclair Unit of Human Nutrition at the University of Reading, at the time.
‘We believe the fibre and polyphenols in apples are important, and apples are a popular fruit among all ages, which are easy to eat and make great snack foods.’
How an apple a day also helps keep the pounds away: Plant compounds can reduce amount of energy absorbed from foods
An apple a day not only keeps the doctor at bay – it also helps you shed the pounds, according to researchers.
Fruit and vegetables that contain high levels of flavonoids seem to stop people putting on weight.
Flavonoids are plant compounds found in berries, apples, pears, strawberries and radishes.
They have long been celebrated for their antioxidant effect, which is thought to help prevent cell damage.
But experts also think that the compounds may also help reduce the energy – particularly from sugar – that is absorbed from food.
In 2016, researchers at the University of East Anglia (UEA) and Harvard Medical School found that certain flavonoids were linked to maintaining a healthy weight, and even helped people lose a little.
Eating the flavonoids contained in an 80g (2.8oz) handful of blueberries every day for four years would help people lose about 2lb 10oz.
By comparison, the average woman in the same period would usually put on about 2lb 3oz, and the average man 4lb 6oz.
In the study, published in the British Medical Journal, experts examined data for 124,086 men and women in the U.S. over a 24-year period.
The research focused on three large groups of people – one featuring women with an average age of 36 at the start of the study, another with women aged 48, and the third for men with an average age of 47.
Professor Aedin Cassidy, from the UEA’s Norwich Medical School, said: ‘This is the first large study to examine the associations between consumption of all flavonoids and weight gain in middle-aged and older adults.
‘Most adults gain weight as they age and even small increases in weight can have a substantial impact on risk of high blood pressure, developing heart disease, cancer or diabetes – so strategies to help individuals maintain a healthy weight in middle-age are needed.
‘We found that an increased consumption of most flavonoids was associated with weight maintenance, and even a modest weight loss. The results were found to be consistent across men and women, and different ages.
‘However losing even small amounts of weight, or preventing weight gain, can improve health and these modest effects were seen with a small, readily achievable increase in intake of many of these fruits.
‘Just a single portion of some of these fruits per day would have an important impact on health at a population level.’
Professor Cassidy said the strongest links were found for foods containing anthocyanins, which are found in blueberries, strawberries, cherries, blackberries, grapes, radishes and blackcurrants.
She said: ‘We also found that flavonoid polymers – found in tea and apples – were particularly beneficial, along with flavonols – found in tea and onions.’