Their study published in the journal PLOS One identified a variant of the GRIN2A gene (CC-type) which could protect against Parkinson's when combined with a high caffeine intake through coffee consumption.
It means that those with the gene can boost protection against Parkinson’s Disease (PD) by drinking more coffee. However, those with another variant of the GRIN2A gene (TC type) already have protection and their defence against PD will not be boosted by increased caffeine intake.
“Caffeine integrates with a dopamine receptor that regulates the flow of calcium into the cell. As dopamine is part of the human reward system, and the interaction of caffeine with it, it has been speculated that individuals with certain genetic variations are not “rewarded” to the same extent by a cup of coffee, and therefore would not enjoy the same protective effect as others. The newly published study shows that GRIN2A can be a part of such a genetic predisposition,” said the researchers.
Under the study, the researchers analysed the genetic variants in GRIN2A in 193 PD patients and 377 controls across two counties in south east Sweden. They found differences between those with a CC GRIN2A and a TC GRIN2A genotype.
They distinguished between light (under 237.8 mg/day) or heavy caffeine consumers (over 237.8 mg/day) using questionnaires.
CC and TC types
Those with in the CC group who had a heavy caffeine intake reduced their PD risk by 47% compared to those with a low caffeine intake.
But those with in the TC cohort already had a 47% PD risk reduction regardless of the caffeine dose “Increasing caffeine dose does not have any further additive effects,” said the researchers.
However: “...PD susceptible CC genotype carriers can get benefit from increasing amount of caffeine intake for PD risk reduction by 58% with 200–≤400 mg/day, by 80% with 400–≤600 mg/day, and by 79% with >600 mg/day,” said the researchers.
Sweden had a high per capita roasted coffee consumption than international standards at 9 kg in 2004. By comparison France had a 4.4 kg rate and the Netherlands 7.1%
Under the study, the CC genotype was the most common. 159 PD patients and 284 in the control group had this genotype compared to 30 (PD) and 88 (control) with a TC genotype. Five in the control group and four in the PD group had an alternative TT genotype.
PLOS One, 9(6): e99294
‘Caffeine Interaction with Glutamate Receptor Gene GRIN2A: Parkinson's Disease in Swedish Population’
Authors: Naomi Yamada-Fowler, Mats Fredrikson, And Peter Söderkvist