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 coffee 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 nutritiongene 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 established biological effects of coffee intake, but the impact on future health is virtually unknown.