Coffee could combat both Parkinson's disease and a form of dementia, research suggests.
Two compounds, including caffeine, in the pick-me-up work together to prevent the accumulation of a toxic protein in the brains of mice.
This protein, known as alpha-synuclein, is associated with both Parkinson's and dementia with lewy bodies (DLB).
Tests on rodents genetically at risk of both diseases showed the combination of caffeine and the compound EHT prevented alpha-synuclein from building-up after just six months.
The scientists now hope caffeine and EHT could be combined into a drug to help treat Parkinson's and DLB in humans, which are both incurable.
The research was carried out by Rutgers University and led by neurologist Dr M Maral Mouradian.
Nearly one million Americans are expected to be diagnosed with Parkinson's by 2020, according to figures. Around 145,500 have been diagnosed in the UK.
PD is a neurodegenerative disorder that mainly affects the dopamine-producing brain networks in the substantia nigra.
Symptoms include shaking, stiffness, and difficulty walking, balancing and coordinating.
Dementia with Lewy Bodies (DLB) is a type of dementia that shares symptoms with both Parkinson's and Alzheimer's. It occurs when alpha-synuclein appears in nerve cells in the brain.
Alpha-synuclein's function in a healthy brain is unclear. When it clumps, it can lead to cell death, which is associated with both PD and DLB.
Treatments for both diseases focus on reducing the protein's gene expression and blocking its aggregation.
DLB affects around 1.3million in the US, according to the Lewy Body Dementia Association. And it makes up between 10 and 15 per cent of all 850,000 dementia cases in the UK, Alzheimer's Society states.
The researchers analysed newborn mice who expressed a gene that caused alpha-synuclein to aggregate in their brain.
The rodents were given either 50mg/kg of caffeine, 12mg/kg of EHT or a combination of the two mixed in their food or water every day for six months.
Tests were then carried out to assess the animals' motor, learning and memory skills, which reflects activity in different parts of the brain.
When given alone, neither caffeine nor EHT had any effect. But the mice who took the two compounds together had higher test scores.
The rodents were then euthanised and their brains examined. This revealed EHT and caffeine together boosted the activity of the protein PP2A, which prevented the accumulation of alpha-synuclein clumps.
The compound coupling also led to reduced brain inflammation, which is a hallmark of PD.
The study was published in the Proceedings of the National Academy of Sciences.
EHT is found in a coffee bean's waxy coating and is unrelated to caffeine. A derivative of the 'happy hormone' serotonin, it has been found to have antioxidant and anti-inflammatory properties in past studies.
Dr Mouradian stressed further studies are required to determine the correct ratios of caffeine and EHT to help protect people from PD and DLB.
'EHT is a compound found in various types of coffee but the amount varies,' she said.
'It is important that the appropriate amount and ratio be determined so people don't over-caffeinate themselves, as that can have negative health consequences.'
Caffeine has previously been found to preserve brain health, with the role of coffee's thousands of other compounds being less clear until now.
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