The study involved 124 older adults (65-88) who were thoroughly cognitively assessed, given brain scans, and had a fasting blood sample taken. They were then followed for 2 to 4 years, during which their cognitive status was re-assessed annually. Of the 124 participants, 69 (56%) were initially assessed as cognitively normal (average age 73), 32 (26%) with MCI (average age 76.5), and 23 (19%) with dementia (average age 77). The age differences were significant.
Those with MCI on initial assessment showed significantly lower levels of caffeine in their blood than those cognitively healthy; levels in those with dementia were also lower but not significantly. Those initially healthy who developed MCI over the study period similarly showed lower caffeine levels than those who didn’t develop MCI, but again, due to the wide individual variability (and the relatively small sample size), this wasn’t significant. However, among those with MCI who progressed to dementia (11, i.e. a third of those with MCI), caffeine levels were so much lower that the results were significant.
This finding revealed an apparently critical level of caffeine dividing those who progressed to dementia and those who did not — more specifically, all of those who progressed to dementia were below this level, while around half of those who remained stable were at the level or above. In other words, low caffeine would seem to be necessary but not sufficient.
On the other hand (just to show that this association is not as simple as it appears), those already with dementia had higher caffeine levels than those with MCI who progressed to dementia.
The critical factor may have to do with three specific cytokines — GCSF, IL-10, and IL-6 — which all showed markedly lower levels in those converting from MCI to dementia. Comparison of the three stable-MCI individuals with the highest caffeine levels and the three with the lowest levels, and the three from the MCI-to-dementia group with comparable low levels, revealed that high levels of those cytokines were matched with high caffeine levels, while, in both groups, low caffeine levels were matched to low levels of those cytokines.
These cytokines are associated with inflammation — an established factor in cognitive decline and dementia.
The level of coffee needed to achieve the ‘magic’ caffeine level is estimated at around 3 cups a day. While caffeine can be found in other sources, it is thought that in this study, as in the mouse studies, coffee is the main source. Moreover, mouse research suggests that caffeine is interacting with an as yet unidentified component of coffee to boost levels of these cytokines.
It’s suggested that the reason high levels of caffeine don’t appear to benefit those with dementia is because higher levels of these cytokines have become re-established, but this immune response would appear to come too late to protect the brain. This is consistent with other evidence of the importance of timing.
Do note that in mouse studies, the same benefits were not associated with decaffeinated coffee.
While this study has some limitations, the findings are consistent with previous epidemiologic studies indicating coffee/caffeine helps protect against cognitive impairment and dementia. Additionally, in keeping with the apparent anti-inflammatory action, a long-term study tracking the health and coffee consumption of more than 400,000 older adults recently found that coffee drinkers had reduced risk of dying from heart disease, lung disease, pneumonia, stroke, diabetes, infections, injuries and accidents.