Italian researchers reported in the September 11, 2008, online issue of the British Medical Journal what is already known:
“Greater adherence to a Mediterranean diet is associated with a significant improvement in health status, as seen by a significant reduction in overall mortality (9%), mortality from cardiovascular diseases (9%), incidence of or mortality from cancer (6%), and incidence of Parkinsons’s disease and Alzheimer’s disease (13%). These results seem to be clinically relevant for public health, in particular for encouraging a Mediterranean-like dietary pattern for primary prevention of major chronic diseases.”
Methodology
Researchers, mostly at the University of Florence, performed a meta-analysis of 12 other published studies that looked at the effects of a Mediterranean-style eating pattern on health and longevity. [Meta-analyses are popular, in part, because they are cheap. This study required no specific funding.]
Most, if not all, of these 12 studies were observational, and involved 1,574,299 participants. Six of the 12 studies were in Mediterranean countries, the others were in the U.S., northern Europe, and Australia. Study participants were followed between 3.7 and 18 years.
The researchers devised their very own Mediterranean diet scale based on study participants’ intake of various foods. Participants were given a point if they had higher than average intake of vegetables, fruits, legumes, cereals, fish, and red wine during meals. They were given a point if they had lower than average intake of red meat, processed meats, and dairy products. Due to differences among the 12 studies, “the total adherence scores…varied from a minimum of 0 points indicating low adherence to a maximum of 7-9 points reflecting high adherence to a Mediterranean diet.”
(This version of a Mediterranean diet score is problematic. Curiously, olive oil – the predominant source of fat in the traditional Mediterranean – is not in the score. Olive oil is a key characteristic of the Mediterranean diet. Furthermore, the study authors also state that dairy products are “presumed not to form part of a Mediterranean diet.” Most experts would argue that cheese and yogurt are a significant part of the Mediterranean diet, if only in low amounts. I also doubt that participants in the 12 original studies were surveyed whether they drank red wine – as contrasted with white – and whether it was with meals or not. I admit I did not read each of the 12 component studies. The underlying cause of this idiosyncratic definition of the Mediterranean diet is that the 12 original studies themselves used different definitions of the Mediterranean diet. The meta-analysts had to pigeonhole the data. There are a handful of respected Mediterranean diet scores in existence, but the authors of this study couldn’t apply them across the board due to database inconsistency or inadequacy.)
Results
“The cumulative analysis of 12 cohort studies shows that a two point increase [emphasis added] in the score for adherence to a Mediterranean diet determines a 9% reduction, in overall mortality, a 9% reduction in mortality from cardiovascular diseases, a 6% reduction in incidence of or mortality from neoplasm [cancer], and 13% reduction in incidence of Parkinson’s disease and Alzheimer’s disease.”
The only one of the 12 original studies focused on Alzheimer’s disease, and it showed a 17% reduction in participants with high adherence to the Mediterranean diet. The two studies that focused on Parkinson’s disease revealed a 7% reduction in men, and 15% reduction in women. These reduced incidence figures, again, apply to a two-point increase in Mediterranean diet adherence score.
Discussion
The authors indicate that their report is the first ever meta-analysis of the data associating the Mediterranean diet with reduced mortality and chronic disease in the general population. Congratulations, guys!
The authors’ idiosyncratic Mediterranean diet score is unusual and won’t be widely adopted. However, the 12 studies comprising the meta-analysis did have reasonable Mediterranean diet characteristics.
Combining Alzheimer’s data with Parkinson’s data doesn’t make sense to me, nor did the authors try to explain it. You could lump them into the category of “neurodegenerative diseases,” but they aren’t the only ones by any means. The single Alzheimer’s study, by the way, was quite small compared to the two Parkinson’s studies.
Nearly all the popular media stories reported the findings as I did in my first paragraph above, which may be misleading. The specific improvements in mortality and various disease rates is per two-point increase in Mediterranean diet score. For example, consider the 9% reduction in overall mortality. If a population increased its Mediterranean score by four points, would overall mortality be reduced by 18%? I’ve read this study four times and cannot answer my own question. But I suspect that the answer is “yes.” So the news here may better than it seems at first blush.
In other words: If a population’s score goes from 5 to 7, the death rate is reduced by 9%. If that same population then moved its score from 7 to 9, would mortality improve another 9%? I think so, but this study as written does not make it clear.
I’m starting to see why the popular media simplified the study findings. The reporting on this study is amazingly uniform. They must have all gotten the same news release.
Of course, “populations” don’t die or get cancer, heart attacks, strokes, Alzheimer’s, or Parkinson’s disease. Individuals do that. If I as an individual had a low Mediterranean diet score, I’d try to improve my score by at least two points. A good place to start would be a review of the Mediterranean diet.
Steve Parker, M.D.
Reference: Sofi, Francesco, et al. Adherence to Mediterranean diet and health status: Meta-analysis. British Medical Journal, 337; a1344. Published online September 11, 2008. doi:10.1136/bmj.a1344
Advanced Mediterranean Diet 