Anxiety and sleep changes
Many coffee drinkers are familiar with "coffee jitters", a nervous condition that occurs when one has had too much caffeine. It can also cause anxiety and irritability, in some with excessive coffee consumption, and some as a withdrawal symptom. Coffee can also cause insomnia in some. In others it can cause narcolepsy.
Coffee causes staining of the teeth.
Paper coffee filters have a property that binds to lipid-like compounds which allows it to remove most of the cafestol and kahweol found in coffee. Brew methods which do not use a paper filter, such as the use of a press pot, fail to remove any cafestol and kahweol from the final brewed product. In contrast, drip brewing with a paper filter removes most of the cafestol and kahweol from the coffee.
Iron deficiency anemia
Coffee consumption can lead to iron deficiency anemia in mothers and infants. Coffee also interferes with the absorption of supplemental iron.
Coronary artery disease
A 2004 study tried to discover why the beneficial and detrimental effects of coffee conflict. The study concluded that consumption of coffee is associated with significant elevations in biochemical markers of inflammation. This is a detrimental effect of coffee on the cardiovascular system, which may explain why coffee has so far only been shown to help the heart at levels of four cups (24 fl oz or 600 mL) or fewer per day.
The health risks of decaffeinated coffee have been studied, with varying results. One variable is the type of decaffeination process used; while some involve the use of organic solvents which may leave residual traces, others rely on steam.
A study has shown that cafestol, a substance which is present in boiled coffee drinks, dramatically increases cholesterol levels, especially in women. Filtered coffee contains only trace amounts of cafestol.
Polymorphisms in the CYP1A2 gene may lead to a slower metabolism of caffeine. In patients with a slow version of the enzyme the risk for myocardial infarction (heart attack) is increased by a third (2–3 cups) to two thirds (>4 cups). The risk was more marked in people under the age of 59.