From the Annals of Mebbe: "Intensive Use" of Olive Oil Reduces Stroke Risk

More favorable publicity for the Mediterranean diet re the reduction of vascular risks; but way-big caveat emptor.

"Intensive use" of olive oil—meaning its use in cooking and dressing*—appeared to lower the risk of stroke over the course of ~5 years, by as much as 40% or so, in a newly published cohort study of 7625 elderly (>65 years) French residents. However, the 95% confidence interval for this impressive and statistically significant risk reduction (comparing intensive users with nonusers) was gaping: 6%, 63%.

In addition, the study authors attempted to correlate the mean plasma oleic acid proportion,** as an indirect indicator of olive oil consumption, with a reduction of stroke risk among the cohort. But the differences in mean proportions among the nonusers, moderate users, and intensive users—although statistically significantly different—were tiny. Specifically the respective proportion values for each of the subgroups were 19.9% vs 20.5% vs 20.7%. Nevertheless the authors were evidently able to pound out statistical significance among these values, despite the fact that the biggest absolute difference was only 0.6%. And they then were able to associate the higher values with a statistically reduced stroke risk. If nothing else, I applaud them for their statistical prowess and/or luck.

Official commenters on the study, Scarmeas and Dauchet, provide a number of caveats when interpreting these results (as do, appropriately, the study authors themselves)—not the least of which is the inability to tease out the single contribution of olive oil, which is necessarily consumed with other, potentially risk-reducing, foods.

* As opposed to one or the other or neither.
** Meaning plasma oleic acid as a proportion of plasma fatty acids.