Abstract
The issue of whether coffee is detrimental or beneficial to health has been studied in a large number of observational and clinical studies. Some observational studies have shown an association between coffee and coronary heart disease (CHD), while others have not. Both clinical trials and observational studies have shown that coffee consumption affects some CHD risk factors, e.g. plasma total homocysteine and serum total cholesterol. Studies on the association between coffee consumption and health have shown protective effects against type 2 diabetes, Parkinson’s disease and Alzheimer’s disease, whereas the protective effect against certain forms of cancer and possible hazards with regard to reproductive health are still debated. This review reports on the association between coffee intake and homocysteine and blood lipids in light of the results of studies by this group. A review of published papers on the relevant issues found that protective effects of cof fee have been reported for type 2 diabetes, Parkinson’s disease and Alzheimer’s disease. These results are based on observational studies. More studies with adequate control of confounding variables are needed to confirm these findings. There are at present no relevant biological explanations for any protective effect. Studies by this group have confirmed that even filtered coffee has a total cholesterol-increasing effect. Whether this is due to changes in filter-paper quality or other unknown mechanisms is not clear. The homocysteine-raising effect of coffee is mainly seen among subjects with the methylenetetrahydrofolate reductase (MTHFR) 677TT polymorphism, demonstrating a nutrition_/gene effect modification. In conclusion, the effects of coffee on blood lipids and plasma homocysteine are firmly based, but the studies reflect a certain heterogeneity, in part explained by genetic susceptibility. The coffee_/health issue is still pending; there are certain firmly establ i shed biological effects of coffee intake, but the impact on future health is virtually unknown. Keywords: blood lipids; coffee; coronary heart disease; homocysteine; reproductive hazards
Highlights
The issue of whether coffee is detrimental or beneficial to health is not new
No plausible mechanism was known to explain the homocysteine-raising effect of coffee, but a recent observational study showed a positive association between caffeine intake and homocysteine concentrations [90]
This has been followed by a randomized cross-over trial by Verhoef et al, where caffeine capsules were compared with filtered coffee, which showed that caffeine is partly responsible for the total homocysteine (tHcy)-raising effect of coffee, since caffeine had only 25Á/50% of the tHcy-raising effect compared with paper-filtered coffee with a similar amount of caffeine [95]
Summary
The issue of whether coffee is detrimental or beneficial to health is not new. King Gustav III of Sweden (1746Á/1792) decided that coffee was pure poison. This may seem surprising, but the major reasons are the incomplete knowledge of the causal models (i.e. there are other unknown factors aetiologically associated with the disorder) and non-differential misclassification of the exposure variables biasing the results towards null Coffee, being such a common beverage with obvious central stimulating effects but seemingly low nutritional value, has been studied in a number of epidemiological studies aiming at a broad array of health issues. Thelle et al concluded in their review that the incongruity of cross-sectional data points to a relationship between coffee and cholesterol in some populations, which needs to be further explored [56] This led to an increased interest in the possible effects of different brewing methods, first examined by Førde et al [57] and later followed up by Dutch and Finnish groups [51, 58]. Intervention studies on the association between unfiltered and filtered coffee and serum cholesterol are shown in Tables 2 and 3, respectively
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