While coffee is neutral or even helpful in moderate amounts, drinking excessive amounts may cause tremors, sleep problems and stress. Caffeine is considered slightly unhealthy for people with high blood pressure. Some diabetics have also reported that coffee causes spikes in their blood sugar levels. Caffeine is not recommended for pregnant women because it can affect the unborn baby through the placenta.
As of 2014, some doctors state that the health benefits of caffeine outweigh the risks but caution certain groups of people nevertheless. Unfiltered coffee, which is either boiled or espresso, is associated with an increase in cholesterol. Although coffee is not generally thought to increase the risk of heart disease, studies have found that some people have a common genetic mutation that slows the metabolism of caffeine.
Some of the health risks associated with coffee come not from the drink but from its additions. Studies reporting health benefits have typically studied the effects of coffee drunk black or with small amounts of milk and sugar. Popular chain coffee shops can have up to 500 calories per drink, which accounts for a significant portion of someone's daily calorie allowance. If the increase in calories is not accounted for, it can cause weight gain, which can lead to type 2 diabetes.