Table 1.

Effects of coffee on single health conditions.

Cardiovascular disease	Habitual coffee consumption was consistently associated with a lower risk of cardiovascular diseases mortality [7,31]. Compared to non-coffee drinkers, risk was reduced by 19% and the largest reduction in relative risk was found at three cups per day [7,34,35]. Coffee consumption may have a protective effect on the risk of stroke [36,37], especially in women [38]. Research found a 30% lower risk of mortality from stroke of coffee consumers compared to non-drinkers [7]. The reduced risk for cardiovascular conditions is related to the antioxidant effects of coffee [26,39].
Type-2 Diabetes	Polyphenolic coffee compounds have beneficial effects on insulin and glucose metabolism [26,31]. Coffee consumption was associated with a lower risk of developing type 2 diabetes [7], with a stronger effect for women [40]. An intake of three to four cups of coffee/day seems to lower the risk by 25% compared to no coffee or less than two cups a day [34,41,42]. A meta-analysis concluded that the risk to develop type 2 diabetes decreased by 6% for each cup-per-day increase in consumed coffee [43].
Liver Conditions	Coffee consumption is related to a lower risk of developing several liver conditions [44,45]. There is an inverse association between coffee consumption and liver cancer [46,47]. Phenolic compounds, melanoidins, and caffeine are responsible for antioxidant effects in the liver [26].
Neuro-degenerative disorders	Lifelong, regular and moderate coffee consumption might have a beneficial effect on physiological, age-related cognitive decline/dementia [48,49], Parkinson’s disease [50,51], and Alzheimer’s disease [52,53]. The potential beneficial effects of coffee on mental health seem to be related to the neuroprotective effect of caffeine [26,50].
Depression and anxiety	Caffeine and other polyphenolic compounds of coffee have been associated with positive effects on mental health, for example behavior, mood, depression, and cognition [7,54]. On the other hand, high caffeine consumption is associated with anxiety and nervousness. Positive effect on mood is influenced by time of consumption, being highest in the late morning [55]. Caffeine seems to be more beneficial for habitual consumers [56]. Coffee consumption had a consistent association with lower risk of depression [26,57] and to relieve depressive symptoms [58].
Cancer	The International Agency for Research on Cancer (IARC) evaluated in 2016 a database of 1000 observational and experimental studies on coffee and cancer and concluded that there are no clear associations between coffee drinking and cancer at any body site. Coffee was classified as an agent “not classifiable as to carcinogenicity to humans”. There is evidence for a lower risk of cancer in high versus low coffee consumption [7]. Phytochemical compounds in coffee (diterpenes, melanoidins, polyphenols) may have beneficial effects at the cellular level, for example inhibiting oxidative stress and damage [26]. There is evidence that coffee intake is associated with a reduced risk of certain cancers [30,59].
Lung and gastric cancers	An adverse effect of coffee consumption has been seen in an increased risk of lung and gastric cancers. In this case, it is important to consider the potentially modifying effect of associated smoking habits. A subgroup analysis showed that the association was significant only in studies that did not adjust for smoking behavior [7,26].
Blood pressure	Coffee consumption has been associated with a rise in blood pressure [26]. Coffee intake raises blood pressure in non-coffee-drinkers, but not in habitual coffee drinkers. On the other hand it was observed that the antioxidant compounds of coffee might counteract the effects of caffeine in raising blood pressure [26]. Research results are conflicting and the association between coffee consumption and blood pressure remains unclear [60].
Pregnancy	Negative associations of coffee and caffeine intake were mostly pregnancy-related (low birth weight, pregnancy loss, preterm birth, childhood leukemia) [7,26,61,62]. The European Food Safety Authority (EFSA) [32] recommends that a moderate caffeine intake of 200 mg/day does not increase the risk of any pregnancy-related complication. Still, the association between coffee/caffeine and reproductive health outcomes needs further investigation as available data are insufficient and the role of confounding (e.g., diet, smoking etc.) factors is unclear [61].
Bone fracture	A negative association between coffee consumption and bone fracture was seen in women [7]. A 14% higher risk was found in high versus low coffee consumption [63]. The increased risk in women seems related to caffeine and its potential influence on calcium absorption [64] and bone mineral density [65]. The systematic review by Wikoff et al. [28] concludes that a caffeine intake of 400 mg/day was not associated with negative effects on fracture, bone mineral density, and calcium metabolism.