Mediterranean diet, Biobank & dementia

The potential link between the Mediterranean diet and dementia risk was explored in a recent study titled "Mediterranean diet adherence is associated with lower dementia risk, independent of genetic predisposition: findings from the UK Biobank prospective cohort study" by Shannon et al.

The UK Biobank, a long-term population-based cohort study that began in 2006 and recruited over 500,000 participants, provided the base data for this investigation. After selection criteria were applied, 60,298 participants were followed for an average of 9.1 years, during which 882 dementia cases were reported.

The Mediterranean diet, with its claimed health benefits, was assessed using two scoring systems: the MedDiet Adherence Screener (MEDAS) score and the MedDiet PYRAMID score. These systems assigned one point for meeting specific criteria, making no distinction for exceeding targets. Researchers also added a third scoring system (which allowed partial points) but found it provided only marginal improvements in differentiating dietary patterns.

Participants were divided into low, medium, and high adherence groups based on the MEDAS score. The high adherence group displayed healthier characteristics, such as more women, lower obesity rates, higher education levels, lower smoking rates, and greater physical activity. We had the usual "healthy person confounder" therefore. Notably, the PYRAMID score failed to provide a characteristics table, making it challenging to assess this system's groupings and potential confounders. (As it happened, the PYRAMID score found nothing, so this ended up not being an issue).

The study claimed that higher adherence to the Mediterranean diet was associated with a lower risk of dementia, but that's not what the results showed. Out of six outcomes examined, four were non results. That was the majority. Researchers implied that the PYRAMID scoring system achieved a signficiant result, but it didn't.

The discussion section acknowledged the strengths and limitations of the study. Strengths included a large sample size and consideration of genetic risk factors. Limitations included the inability to establish causation, potential inaccuracies in diet questionnaires, concerns about reverse causality, and the unavailability of data on specific diet components like sofrito (a sauce made from tomatoes, peppers, garlic, onions and olive oil) in the UK population. The study also noted that UK Biobank participants might not represent the broader UK population due to their generally better health and higher socioeconomic status.

On the whole, this was another poor population study, which claimed more than it found, once again showing the inadequacies of these kinds of studies.

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