By Morgan Wharton and Jessica Cote
Most Americans drink coffee every day.1 The caffeine in coffee helps us stay alert but also may cause jitteriness and interfere with sleeping. A few studies suggest that decaffeinated coffee also has health benefits, perhaps because of antioxidants or acids in the coffee bean.2
What Are The Health Benefits Of Drinking Coffee?
For years medical experts advised people to drink less coffee, mostly because of research suggesting coffee might increase the risk of heart disease. However, numerous studies conducted recently have discovered coffee’s unexpected health benefits. Like all well-designed research, most of these studies considered the impact of age, sex, body mass index (BMI), physical activity, tobacco use, and whether family members had developed cancer. By controlling for those factors, researchers made sure they could separate coffee’s impact on health from the effects of people’s lifestyle, family history, and previous health problems.
Meta-analyses are a kind of statistics that combine data from several comparable studies to make one very large study. These results are usually more accurate than any one study can be. Taken together, three meta-analyses suggest that drinking about four or more cups of coffee per day may reduce the chances of getting colorectal cancer by 11-24%.345
Endometrial (uterine) Cancer
Using data from 67,470 women who participated in the Nurses’ Health Study, researchers found that women who drank four or more cups of coffee per day were 25% less likely to develop endometrial cancer than women who drank only one cup of coffee per day. Compared to women who did not drink any coffee, those who drank four cups or more per day were 30% less likely to develop endometrial cancer. Decaffeinated coffee was just as effective as caffeinated coffee, but caffeinated tea did not lower the risk of endometrial cancer.6
Liver Cancer And Cirrhosis (Scarring of the Liver/Chronic Liver Disease)
One study found people who drank one or two cups of coffee per day had a slightly lower risk of getting the most common type of liver cancer compared to non-drinkers, but people who drank three or four cups of coffee were about half as likely as non-drinkers to get this kind of liver cancer. Meanwhile, people who drank five or more cups per day had an even lower risk than that (about one-third the risk of non-drinkers).7
Similarly, a study in Japan found a 76% decrease in the risk of that type of liver cancer in people who drank at least five cups of coffee per day compared to those who did not drink coffee. The strongest benefit was seen in individuals with hepatitis C, a disease which increases a person’s risk of developing liver cancer, although the researchers were not sure why.8
A study of 120,000 Americans over an 8-year period found a 22% decrease in the chances of developing cirrhosis for each daily cup of coffee. In Norway, a 17-year study of 51,000 citizens found that those who drank two or more cups of coffee per day were 40% less likely to develop cirrhosis compared to those who did not consume coffee.9
Using data from two enormous studies, the Nurses’ Health Study and the Health Professionals Follow-up Study, researchers found that men and women who drank more than three cups of caffeinated coffee per month were 17% less likely to develop basal cell carcinoma compared to people who drank less than one cup per month. Basal cell carcinoma is the most common and least dangerous type of skin cancer. Drinking decaffeinated coffee did not affect basal cell carcinoma.10
A 2014 study in the Journal of the National Cancer Institute found that the more coffee participants drank, the less likely they were to develop malignant melanoma over a 10 year period. Melanoma is the most dangerous form of skin cancer. Almost 450,000 whites, aged 50-71, participated in the study. Researchers found that drinking four or more cups of coffee per day was linked to a 20% lower risk of getting malignant melanoma. Once again, drinkers of decaffeinated coffee lost out. Their risk of getting melanoma was no different from that of non-coffee drinkers. Coffee drinking, however, did not affect the least dangerous form of melanoma, called melanoma in situ.
Remember that no matter how much coffee with caffeine you drink, the best way to prevent skin cancer is still to limit your time exposed to the sun and ultraviolet light! 11
Type 2 Diabetes
People in Finland consume more coffee than almost any other nation, and a study of 14,000 people over 12 years found that men who drank 10 or more cups of coffee daily had a 55% lower risk of developing type 2 diabetes than men who drank 2 cups of coffee a day or fewer. Even more dramatic, women who drank 10 or more cups per day had a 79% lower risk of developing type 2 diabetes than those who drank fewer than 2 cups daily.12
A different Finnish study of 5,000 sets of identical twins found that individuals who drank more than seven cups of coffee per day had a 35% lower risk of type 2 diabetes than their twins who drank two cups or fewer per day.13 Because identical twins are so biologically similar, the difference in disease risk is very likely caused by coffee consumption levels. Studies of fewer people in other countries have found less dramatic but similarly positive results.
A study of more than 8,000 Japanese-American men found that men who did not drink coffee at all were three to five times more likely to develop Parkinson’s disease within 30 years than men who drank four and a half cups or more of coffee per day.14
Because suicide may be related to alcohol intake, medications, and stress levels, suicide studies took those factors into account. A 10-year study of 128,000 people in California found that the risk of suicide decreased by 13% for every additional cup of coffee consumed per day. Even one cup of coffee per day seemed to reduce the risk of suicide. A different 10-year study of 86,000 women found a 50% lower risk of suicide for those who drank two or more cups of coffee per day compared to women who did not drink coffee.15
Brain Power and Aging
A study of 676 healthy men born between 1900 and 1920 suggested that coffee helped with information processing and slowed the cognitive decline typical of aging. Cognitive functioning was measured by the Mini-Mental State Examination, a 30 point scale. Men who regularly consumed coffee experienced an average decline of 1.2 points over 10 years, while men who did not drink coffee saw a decline of 2.6 points over 10 years. Men who drank three cups of coffee per day declined only 0.6 points over 10 years.16
Even old mice are sharper with caffeine: a study using a mouse model of Alzheimer’s disease showed that coffee actually reversed the cognitive decline and slow-down in processing that occurred with age. Mice given caffeine in their water showed signs of recovering their memory during testing.17
What about the risks?
Two separate studies found that 300 mg of caffeine (two to three cups of coffee) decreased a woman’s chances of getting pregnant by more than a third. This same amount of coffee also increased the chances of women having low birth-weight babies by 50%. These studies took into account potentially influential factors such as contraception used in the past and infertility history.18
According to data from the Nurses’ Health Study, women aged 65 and over who drank more than four cups of coffee per day had almost 3 times as many hip fractures over the next six years as women who did not drink coffee. Researchers took important factors into consideration such as how much calcium the women consumed each day.19
Parkinson’s Disease among post-menopausal women taking estrogen-only hormone therapy
Other researchers used data from the Nurses’ Health Study to evaluate the risk of Parkinson’s disease among women who drank coffee while using estrogen medication after menopause. For women who were NOT using estrogen therapy, those who drank four or more cups of coffee per day were about half as likely to develop Parkinson’s disease as women who did not drink coffee. For women who did use post-menopausal estrogen, however, those who drank four or more cups of coffee were about twice as likely as those who didn’t drink coffee to develop Parkinson’s.20
Two different meta-analyses found that people who drank five or more cups of coffee per day were 40-60% more likely to develop heart disease compared to those who did not drink coffee at all. Other studies have also shown that high coffee use (five to ten cups per day) increases the risk of heart disease, while moderate consumption (three to four cups daily) was not associated with a higher risk. Only coffee drinkers who consumed more than nine cups a day had a greater risk of dying from heart disease.21 It is important to consider that people drinking close to 10 cups of coffee a day are likely to have other health problems, such as stress or sleep deprivation, and this could contribute to higher risk of heart disease and death regardless of coffee use.
For most people, drinking coffee seems to improve health more than harm it. Many of coffee’s health benefits increase with the number of cups per day, but even one cup a day lowers the risk of several diseases. However, women who want to get pregnant or already are pregnant and women over 65 should probably limit their coffee intake because, in their case, the risks may outweigh the health benefits.
Even though many studies show coffee has benefits, it’s still not clear why. How can one popular beverage help metabolism (for example, lowering the risk of type 2 diabetes) and also protect against a range of cancers? Until further research can solve that puzzle, most adults should continue to enjoy their cup (or two, or three) of Joe. Finally, remember that nearly all studies on coffee and health have been done on adults. Coffee may affect children and teens differently.