"Gosh" said my husband, rustling the newspaper. "You’d better start drinking coffee!"
He’d just come across a report saying that drinking more coffee in one’s middle years is associated with a decreased chance of developing Alzheimer’s disease, or other forms of dementia, in old age. But is this enough to make me want to give up my jasmine dragon-pearl tea?
Not just yet. The actual paper isn’t available yet; all you can read on-line is the abstract, in the up-coming volume of the Journal of Alzheimer’s Disease. And what I can see there is not going to make me pass on my several-times-daily cuppa. Not yet.
The paper is based on data from a longitudinal population health study from Sweden & Finland: people were recruited into the study while middle-aged, in the 1970s, and in 1998 1409 of what was presumably a much larger original group showed up for the end-of-study followup examination. By this time these 1409 individuals were between 65 & 79 years old. They completed survey forms that asked a whole heap of lifestyle-related questions, including how much tea or coffee they drank daily, & were tested for signs of dementia. A total of 61 individuals were diagnosed with some form of dementia, and 48 of those 61 had Alzheimer’s (AD). The study’s authors stated that, after a range of potentially confounding variables had been accounted for, their data showed that those individuals who drank more coffee were less likely to develop either AD or other forms of dementia. And they said that "the lowest risk (65% decreased) was found in people who drank 3-5 cups per day" (Eskelinen et al. 2009).
But there are things left unsaid, & without them I can’t tell whether holding my nose & drinking coffee will have any significant effect on my future health. Because – I don’t know the
relative absolute risk. 65% of what??? Did all the AD occur in the non-coffee drinkers? If not, how many of the coffee-drinkers were affected? The abstract doesn’t offer this information, & neither does the newspaper article based on it (it would have been nice if the journalists had asked these questions too…).
What else wasn’t mentioned: the fact that caffeine in high doses can have negative health impacts. For example, it’s linked to hypertension (high blood pressure) & can cause nausea & insomnia in people who regularly ingest large quantities. So until I’ve seen the paper itself (& maybe not even then) I won’t be giving up my Camellia sinensis habit just yet.
(And for an excellent example in support of the statement that correlation does not equal causation: while high caffeine intake has been linked with loss of calcium from bones, coffee intake appears to be a marker rather than a cause. This is because this particular study found that those drinking lots of coffee also tend to lower their intake of dairy products.)
M.H. Eskelinen, T. Ngandu, J. Tuomilehto, H. Soininen, M. Kivipelto (2009) Midlife coffee and tea drinking and the risk of late-life dementia: a population-based CAIDE study. Journal of Alzheimer’s Disease 16(1)