Appropriately Designed Studies are Required before High Tea or Coffee Consumption is Recommended to Prevent Dementia

We read with interest the article by Hou et al. on a hospital-based case-control study on the association between coffee and tea consumption and the risk of Alzheimer's disease (AD) and vascular dementia (VD), stratified by sex and vascular risk factors [1] .In 278 patients with AD and 102 patients with vascular dementia, the consumption of more than 3 cups of tea or coffee per day was found to be protective against AD and vascular dementia [1] .The protective effect of tea or coffee was more pronounced in women and patients with arterial hypertension [1] .It was concluded that the risk of AD and VD was reduced with the consumption of tea or coffee, although there were differences between genders and vascular comorbidities [1] .The study is noteworthy, but some points should be discussed.The first point is that the study design was not suitable to answer the question of whether coffee or tea consumption actually affects the prevalence of AD or VD.The group sizes were small, the determination of the amount of tea and coffee consumed was imprecise, it is unclear how many subjects mixed tea and coffee with other stimulant beverages, it was not specified which types of tea and coffee were meant, and the quality of the products was not included in the assessment.Since tea and coffee can be heavily contaminated with herbicides and pesticides, it is crucial to know how many of the patients have adapted their drinking habits to the production conditions.The second point is that the patients with AD and VD were asked about the amount of tea or coffee consumption.How was it ensured that patients with memory problems gave reliable answers?How was it ensured that the subjects actually understood the questions on the questionnaire?Furthermore, for patients who have already been diagnosed with dementia, it is irrelevant how much tea or coffee they drank after being diagnosed.The only relevant information for answering the study question is how many cups of tea and coffee they drank before being diagnosed with AD or VD.As answering this question would require even more memory capacity because the events would have occurred even further back, it is quite unlikely that the participants would have been able to solve this task.The third point is that concomitant medications were not included in the analysis.Since certain medications are a risk factor for dementia (e.g., anticholinergics, benzodiazepines, antipsychotics, antidepressants, antiseizure medications, antihistamines, incontinence medications, sleeping pills, antimuscarinics, chemotherapeutics, glucocorticoids, diphenhydramine, antihypertensives, motion sickness medications, analgesics, statins), it would have been crucial to include current medications in the analysis.Fourthly, the influence of gender on the results is not reliable, as the verum and control groups were only matched for age, but not for gender according to the methods.To summarize, this interesting study has limitations that affect the results and their interpretation.Addressing these limitations could strengthen the conclusions and support the message of the study.Before concluding that more than 3 cups of tea or coffee per day is protective against AD and VD, adequately designed and powered studies that take into account all risk factors for AD and VD need to be conducted.In addition, the recommendation to drink tea and coffee to prevent dementia could lead to an increase in the side effects of excessive tea and coffee consumption.