Drinking a lot of coffee every day could potentially cut the risk of developing multiple sclerosis (MS), research suggests.
Consuming more than 900ml (30 fluid ounces) - the equivalent of two Grande coffees in Starbucks - may offer up to a 30% reduced risk, experts found.
Researchers from the Karolinska Institute in Stockholm, Johns Hopkins University in Maryland and the University of California, Berkeley, looked at two studies.
One in Sweden involved 1,620 adults with MS and a comparison group of 2,788 people without MS. The second was a US study of 1,159 people with MS and 1,172 healthy people.
In both studies, people were asked about their coffee consumption and how long they had been drinking coffee for.
The researchers then estimated coffee intake at and before the start of MS symptoms in those who developed the disease, and compared this with healthy groups.
The results showed that the risk of MS was consistently higher among people who drank fewer cups of coffee every day in both studies, even after taking into account other factors that might influence the results.
In the Swedish study, drinking coffee was linked to a lower risk of MS both at the start of symptoms and five and 10 years beforehand. Among those who drank more than six small cups (more than 900ml) every day, there was a 28% to 30% lower risk compared with non-coffee drinkers.
Similar results were found in the US study, with a 26% to 31% lower risk among those drinking more than 948ml daily at least five years beforehand and at the start of symptoms.
The authors, writing in the Journal of Neurology, Neurosurgery and Psychiatry, stressed theirs was an observational study, so no firm conclusions could be drawn about cause and effect.
But they concluded: "Lower odds of MS with increasing consumption of coffee were observed, regardless of whether coffee consumption at disease onset or five or 10 years prior to disease onset was considered.
"In accordance with studies in animal models of MS, high consumption of coffee may decrease the risk of developing MS."
The experts said caffeine is known to have neuroprotective properties, and has been shown to suppress inflammatory responses in the body.
In an accompanying editorial, Elaine Kingwell and Jose Maria Andreas Wijnands, from the University of British Columbia in Vancouver, said previous studies had been inconsistent.
"Although it remains to be shown whether drinking coffee can prevent the development of MS, the results of these thorough analyses add to the growing evidence for the beneficial health effects of coffee," they said.
"The intriguing findings indicate that the role of coffee in the development of MS clearly warrants further investigation, as do the mechanisms that underlie the relationship."
Dr Emma Gray, head of clinical trials at the MS Society, said: "This study provides new evidence that the link between the risk of developing MS and coffee consumption is worth exploring.
"There are more than 100,000 people with MS in the UK and we don’t yet fully understand what causes it.
"While more studies are needed in this area, we welcome any research that offers new insights into risk factors for MS."