A cascade of scientific studies has linked coffee with a reduced risk of diabetes for more than a decade. Scientists in China recently used a strong, representative sample to pull it all together. They culled data from over a million individuals, and integrated and re-examined results to yield an even larger picture. In technical terms, the process is called a “meta-analysis” but, in practice, it’s like doing a new study that is much wider in reach and broader in scope.
The conclusions confirmed what many scientists have been saying all along – that there is an inverse relationship between coffee consumption and the risk of developing diabetes. In laymen’s terms, that means that as coffee consumption goes up, the risk of diabetes comes down.
Pooling data from 30 studies, the Qingdao University team concluded that, on average, coffee appears to reduce the risk of developing diabetes by about one-third. Put another way, they affirmed a 12% decrease in risk for every two cups of coffee consumed.
The Chinese study’s unique contribution is a conclusion based on high-quality studies and a very large subject pool. Reviewing only “prospective studies,” which examine behaviors and outcomes going forward rather than recording past events, the team eliminated risks of hazy recall and subject selection bias that other types of studies allow. That makes the outcomes a broad confirmation of what many scientists have found individually since about 2002.
Decade of Evidence
The literature from which the new study was drawn is extensive. Scores of studies from around the world have all come to the same conclusion – that coffee appears to have a protective effect against diabetes that has something to do with the sugar uptake system in the body. The specific “pathways” vary, but they now appear to point to the same chemical source – the chlorogenic acids found naturally in coffee.
The link between coffee and reduced diabetes risk dates back to a Dutch study done in 2002. Scientists at Vrije University in Amsterdam found that men and women who drank seven cups of coffee a day were half as likely to develop the disease as those who drank two cups or fewer. In 2003, a Harvard study confirmed the findings, finding that men who drank six or more cups of coffee a day had a 54% lower risk of becoming diabetic, while those who drank four or more cups showed a 29% lower risk. At this stage in the research history, scientists looked to caffeine as the source, citing the effect it has on human energy expenditure. But, they also noted that other coffee compounds, including potassium, niacin and magnesium, might positively affect sugar metabolism.
In 2004, a Finnish study found that men who drank three to four cups of coffee a day reduced their diabetes risk by 27%, while women did so by 29%. The more they drank, the higher was the protection, too – men who drank 10 or more cups reducing their risk by 55% and women by 80%. Later that year, a Swedish study also found a lower diabetes risk among heavier coffee drinkers. Men who drank five or more cups a day showed a 40% lower incidence than those who consumed two or fewer cups. For women, the risk reduction was 74% for those who drank five or more cups versus two or less.
The next year found NCA joining with European colleagues to fund two studies to dig deeper into the intriguing data. The American study explored glucose uptake in rats, with results showing that the risk reduction was unique to coffee and not caffeine, with decaf demonstrating the same protective effect. In the European study, coffee’s effect on human glucose tolerance and gastrointestinal hormones was studied, and results showed a positive effect on blood glucose levels that was linked to the availability and chemical action of chlorogenic acids in coffee.
The University of Minnesota was next with a study that found diabetes risk reduction among postmenopausal women – 22% for six or more cups, 16% for four to five cups, and 4% for one to three. Decaf results were even stronger, suggesting that a unique coffee compound was at work. Those drinking six plus cups of decaf saw a 34% reduction in risk, 41% at four to five cups and 2% at one to three. Caffeine alone yielded no protective effect. The researchers now looked to chlorogenic acid as the root of the protection, reducing glucose absorption or inhibiting liver hormone activity. The scientists also pointed to other powerful antioxidant properties , which can protect certain pancreatic cells from damage or promote insulin sensitivity, thereby delaying or preventing diabetes onset.
Later that year, a study at the University of California at San Diego expanded evidence by finding a risk reduction among pre-diabetic subjects that was even stronger than for those with normal fasting blood sugar levels. Pre-diabetics exhibited a 69% reduced risk of developing diabetes, while those with normal sugar levels showed a 62% reduced risk.
Other, more recent studies, have added to the body of evidence. In 2011, researchers at Nagoya University in Japan found that coffee and caffeine improved insulin sensitivity and glucose tolerance in rats whose glucose tolerance had been impaired by diet. The findings enhance prior evidence that coffee and caffeine help regulate hyperglycemia, or high blood sugar, in spontaneously diabetic animals.
Earlier this year, Brazilian scientists concluded that coffee reduces blood sugar and cholesterol levels associated with diabetes. The study looked at the impact of coffee on diabetic and non-diabetic rats, finding that the rats who drank coffee had lower levels of glucose, triglycerides, total cholesterol, creatinine, uric acid and other metabolic markers – for example a 40% decrease in levels of triglycerides and 31% for urea. Looking at the mechanisms behind the protection, the researchers cited the inhibition of sugar transporters by chlorogenic acid and sodium, and other compounds that impact glucose levels. They also noted that coffee is packed with polyphenols, strong antioxidant compounds that reduce the cellular damage by free radicals which, in turn, plays a role in the development of insulin resistance and diabetes.
So, just like the Chinese scientists, if you put all this data together, you come up with a very intriguing conclusion. While the root cause is still not totally understood, the consensus on the impact is extensive. So, next time you’re sipping your coffee, think about the time, effort, energy, talent, and even geographic reach of the work that’s been done, and how all the evidence leads to the same place. The force of science is with you if think you’re sipping your risk away.