Each cup of coffee per day associated with reduced diabetes risk
Consuming a healthy diet was associated with reduced risk for type 2 diabetes among women in all racial and ethnic groups but conferred an even greater benefit for Asian, Hispanic, and black women, according to a new study by researchers at Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital.
"This study suggests that a healthy overall diet can play a vital role in preventing type 2 diabetes, particularly in minority women who have elevated risks of the disease. As the incidence of type 2 diabetes continues to increase at an alarming rate worldwide, these findings can have global importance for what may be the largest public health threat of this century," said lead author Jinnie Rhee, who conducted the research as a doctoral student in the Departments of Epidemiology and Nutrition at Harvard Chan and is currently a postdoctoral fellow in the Division of Nephrology at Stanford University School of Medicine.
The study appears online January 15, 2015 in Diabetes Care.
It's estimated that about 29.1 million people in the U.S. and 47 million around the world have diabetes. The World Health Organization projects that diabetes will be the seventh leading cause of death in 2030. The disease, which is often related to excess body weight and physical inactivity, is more common in African Americans, Latinos, Native Americans, and Asian Americans/Pacific Islanders, and the aged. Previous studies have shown links between diet and risk of type 2 diabetes, but most have been conducted in predominately white populations.
The researchers analyzed data on diet in 156,030 non-Hispanic white women and 2,026 Asian, 2,053 Hispanic, and 2,307 black women in the Nurses' Health Study and Nurses' Health Study II. They adjusted for a variety of factors, such as age, physical activity, smoking, family history of diabetes, alcohol intake, postmenopausal status, menopausal hormone or oral contraceptive use, total caloric intake, and body mass index. The women were followed for up to 28 years and filled out diet questionnaires every four years.
The researchers created a dietary diabetes risk reduction score that included components associated with type 2 diabetes risk. A higher score indicated a healthier overall diet--one with lower intake of saturated and trans fats, sugar-sweetened beverages, and red and processed meats; lower glycemic index foods; and higher intakes of cereal fiber, polyunsaturated fats, coffee, and nuts.
Results showed a protective association of similar magnitude between a healthy overall diet and type 2 diabetes risk in all racial and ethnic groups. Comparing the highest to the lowest quartile of dietary diabetes risk reduction score, healthy diet was associated with a 48% lower risk of diabetes in white, 42% in Asian, 55% in Hispanic, and 32% in black women. When all the minority women were combined into one group, those in the highest quartile of dietary score had a 36% lower risk of diabetes compared with women in the lowest quartile. However, because minority women were initially at higher risk of diabetes than white women, in terms of the actual number of avoidable cases, a healthier diet had greater benefit for minority women. The analysis showed that 5.3 cases of diabetes can be prevented per 1,000 white women per year with a healthier overall diet compared with 8.0 cases that can be prevented per 1,000 minority women per year.
Among the findings was that in both white and minority women, higher glycemic index foods as well as each serving of sugar-sweetened beverages, and red and processed meats were associated with increased risk of diabetes. In contrast, higher intake of cereal fiber (grams/day) and each cup of coffee per day were associated with reduced diabetes risk in both groups.
Increasing consumption of coffee is associated with reduced risk of type 2 diabetes
New research published in Diabetologia (the journal of the European Association for the Study of Diabetes) shows that increasing coffee consumption by on average one and half cups per day (approx 360ml) over a four-year period reduces the risk of type 2 diabetes by 11%. The research is led by Dr Frank Hu and Dr Shilpa Bhupathiraju, Department of Nutrition, Harvard School of Public Health, Harvard University, Boston, MA, USA, and colleagues.
Coffee and tea consumption has been associated with a lower type 2 diabetes risk but little is known about how changes in coffee and tea consumption influence subsequent type 2 diabetes risk. The authors examined the associations between 4-year changes in coffee and tea consumption and risk of type 2 diabetes in the subsequent 4 years.
The authors used observational data from three large prospective, US-based studies in their analysis: the Nurses' Health Study (NHS) (female nurses aged 30-55 years, 1986-2006), the NHS II (younger female nurses aged 25-42 years 1991-2007), and the Health Professionals Follow-up Study (HPFS) (male professionals 40-75 years, 1986-2006). Detailed information on diet, lifestyle, medical conditions, and other chronic diseases was collected every 2 to 4 years for over 20 years.
The availability of these repeated measures and the long-duration of follow-up allowed the authors to evaluate 4 year changes in coffee and tea intake in relation to risk of type 2 diabetes in the following 4 years. They also examined whether the association with diabetes incidence differed between changes in caffeinated and decaffeinated coffee. Diet was assessed every 4 years using a validated food frequency questionnaire. Self-reported incident type 2 diabetes cases were validated by supplementary questionnaires. The final analysis included 48,464 women in NHS, 47,510 women in the NHS II, and 27,759 men in HPFS.
The authors documented 7,269 incident type 2 diabetes cases, and found that participants who increased their coffee consumption by more than 1 cup/day (median change=1.69 cups/day) over a 4-year period had a 11% lower risk of type 2 diabetes in the subsequent 4-years compared to those who made no changes in consumption. Participants who decreased their coffee intake by 1 cup a day or more (median change=-2 cups/day) had a 17% higher risk for type 2 diabetes. Changes in tea consumption were not associated with type 2 diabetes risk.
Those with highest coffee consumption and who maintained that consumption—referred to as "high-stable consumers" since they consumed 3 cups or more per day—had the lowest risk of type 2 diabetes, 37% lower than the "low-stable consumers" who consumed 1 cup or less per day.
The authors say that the higher risk of type 2 diabetes associated with decreasing coffee intake may represent a true change in risk, or may potentially be due to reverse causation whereby those with medical conditions associated with risk for type 2 diabetes (such as high blood pressure, elevated cholesterol, cardiovascular disease, cancer) may reduce their coffee consumption after diagnosis. However, even when cases of cardiovascular disease or cancer were excluded during follow-up, the results were very similar.
While baseline decaffeinated coffee consumption was associated with a lower type 2 diabetes risk, the changes in decaffeinated coffee consumption did not change this risk. Regarding tea consumption, the authors say: "we found no evidence of an association between 4-year increases in tea consumption and subsequent risk of type 2 diabetes. This finding may have potentially been due to the relatively low number of participants who made significant changes to their tea consumption over a 4-year period thereby limiting statistical power to detect true associations. The overall low levels of tea consumption in this group may also be responsible for these findings."
The authors say: "In these 3 large prospective cohorts with more than 1.6 million person-years of follow-up, we observed that increasing coffee, but not tea, intake over a 4-year period was associated with a lower type 2 diabetes risk in the next 4 years. Decreasing coffee intake was associated with a higher type 2 diabetes risk. These changes in risk were observed for caffeinated, but not decaffeinated coffee, and were independent of initial coffee consumption and 4-year changes in other dietary and lifestyle factors."
They add: "Changes in coffee consumption habits appear to affect diabetes risk in a relatively short amount of time. Our findings confirm those of prospective studies that higher coffee consumption is associated with a lower type 2 diabetes risk and provide novel evidence that changes in coffee consumption habits are related to diabetes risk."
Moderate coffee consumption may reduce risk of diabetes by up to 25 percent
Drinking three to four cups of coffee per day may help to prevent type 2 diabetes according to research highlighted in a session report published by the Institute for Scientific Information on Coffee (ISIC), a not-for-profit organisation devoted to the study and disclosure of science related to coffee and health.
Recent scientific evidence has consistently linked regular, moderate coffee consumption with a possible reduced risk of developing type 2 diabetes. An update of this research and key findings presented during a session at the 2012 World Congress on Prevention of Diabetes and Its Complications (WCPD) was summarized in the report.
The report outlines the epidemiological evidence linking coffee consumption to diabetes prevention, highlighting research that shows three to four cups of coffee per day is associated with an approximate 25 per cent lower risk of developing type 2 diabetes, compared to consuming none or less than two cups per day1. Another study also found an inverse dose dependent response effect with each additional cup of coffee reducing the relative risk by 7-8 per cent2.
Whilst these epidemiological studies suggest an association between moderate coffee consumption and reduced risk of developing diabetes, they are unable to infer a causal effect. As such, clinical intervention trails are required to study the effect in a controlled setting. One prospective randomized controlled trial3, tested glucose and insulin after an oral glucose tolerance test with 12g decaffeinated coffee, 1g chlorogenic acid, 500 mg trigonelline, or placebo. This study demonstrated that chlorogenic acid, and trigonelline reduced early glucose and insulin responses, and contribute to the putative beneficial effect of coffee.
The report notes that the association between coffee consumption a reduced risk of type 2 diabetes could be seen as counter intuitive, as drinking coffee is often linked to unhealthier habits, such as smoking and low levels of physical activity. Furthermore, studies have illustrated that moderate coffee consumption is not associated with an increased risk of hypertension, stroke or coronary heart disease4 ,5, 6. Research with patients with CVD has also shown that moderate coffee consumption is inversely associated with risk of heart failure, with a J-shaped relationship.
Finally, the report puts forward some of the key mechanistic theories that underlie the possible relationship between coffee consumption and the reduced risk of diabetes. These included the 'Energy Expenditure Hypothesis', which suggests that the caffeine in coffee stimulates metabolism and increases energy expenditure and the 'Carbohydrate Metabolic Hypothesis', whereby it is thought that coffee components play a key role by influencing the glucose balance within the body. There is also a subset of theories that suggest coffee contains components that may improve insulin sensitivity though mechanisms such as modulating inflammatory pathways, mediating the oxidative stress of cells, hormonal effects or by reducing iron stores.
Coffee protects against diabetes
Coffee, that morning elixir, may give us an early jump-start to the day, but numerous studies have shown that it also may be protective against type 2 diabetes. Yet no one has really understood why.
Now, researchers at UCLA have discovered a possible molecular mechanism behind coffee's protective effect. A protein called sex hormone–binding globulin (SHBG) regulates the biological activity of the body's sex hormones, testosterone and estrogen, which have long been thought to play a role in the development of type 2 diabetes. And coffee consumption, it turns out, increases plasma levels of SHBG.
Reporting with colleagues in the the journal Diabetes, first author Atsushi Goto, a UCLA doctoral student in epidemiology, and Dr. Simin Liu, a professor of epidemiology and medicine with joint appointments at the UCLA School of Public Health and the David Geffen School of Medicine at UCLA, show that women who drink at least four cups of coffee a day are less than half as likely to develop diabetes as non-coffee drinkers.
When the findings were adjusted for levels of SHBG, the researchers said, that protective effect disappeared.
The American Diabetes Association estimates that nearly 24 million children and adults in the U.S. — nearly 8 percent of the population — have diabetes. Type 2 diabetes is the most common form of the disease and accounts for about 90 to 95 percent of these cases.
Early studies have consistently shown that an "inverse association" exists between coffee consumption and risk for type 2 diabetes, Liu said. That is, the greater the consumption of coffee, the lesser the risk of diabetes. It was thought that coffee may improve the body's tolerance to glucose by increasing metabolism or improving its tolerance to insulin.
"But exactly how is elusive," said Liu, "although we now know that this protein, SHBG, is critical as an early target for assessing the risk and prevention of the onset of diabetes."
Earlier work by Liu and his colleagues published in the New England Journal of Medicine had identified two mutations in the gene coding for SHBG and their effect on the risk of developing type 2 diabetes; one increases risk while the other decreases it, depending on the levels of SHBG in the blood.
A large body of clinical studies has implicated the important role of sex hormones in the development of type 2 diabetes, and it's known that SHBG not only regulates the sex hormones that are biologically active but may also bind to receptors in a variety of cells, directly mediating the signaling of sex hormones.
"That genetic evidence significantly advanced the field," said Goto, "because it indicated that SHBG may indeed play a causal role in affecting risk for type 2 diabetes."
"It seems that SHBG in the blood does reflect a genetic susceptibility to developing type 2 diabetes," Liu said. "But we now further show that this protein can be influenced by dietary factors such as coffee intake in affecting diabetes risk — the lower the levels of SHBG, the greater the risk beyond any known diabetes risk factors."
For the study, the researchers identified 359 new diabetes cases matched by age and race with 359 apparently healthy controls selected from among nearly 40,000 women enrolled in the Women's Health Study, a large-scale cardiovascular trial originally designed to evaluate the benefits and risks of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer.
They found that women who drank four cups of caffeinated coffee each day had significantly higher levels of SHBG than did non-drinkers and were 56 percent less likely to develop diabetes than were non-drinkers. And those who also carried the protective copy of the SHBG gene appeared to benefit the most from coffee consumption.
When the investigators controlled for blood SHBG levels, the decrease in risk associated with coffee consumption was not significant. This suggests that it is SHBG that mediates the decrease in risk of developing type 2 diabetes, Liu said.
And there's bad news for decaf lovers. "Consumption of decaffeinated coffee was not significantly associated with SHBG levels, nor diabetes risk," Goto said. "So you probably have to go for the octane!"
Coffee Consumption = Reduced Risk of Diabetes
Drinking more coffee (regular or decaffeinated) or tea appears to lower the risk of developing type 2 diabetes, according to an analysis of previous studies reported in the December 14/28 2009 issue of Archives of Internal Medicine, JAMA
By the year 2025, approximately 380 million individuals worldwide will be affected by type 2 diabetes (1).
Despite considerable research attention, the role of specific dietary and lifestyle factors remains uncertain, although obesity and physical inactivity have consistently been reported to raise the risk of diabetes mellitus. A previously published meta-analysis suggested drinking more coffee may be linked with a reduced risk, but the amount of available information has more than doubled since.
Rachel Huxley, D.Phil, of The George Institute for International Health, University of Sydney, Australia, and colleagues identified 18 studies involving 457,922 participants and assessing the association between coffee consumption and diabetes risk published between 1966 and 2009.
Six studies involving 225,516 individuals also included information about decaffeinated coffee, whereas seven studies with 286,701 participants reported on tea consumption.
When the authors combined and analyzed the data, they found that each additional cup of coffee consumed in a day was associated with a 7 percent reduction in the excess risk of diabetes.
Individuals who drank three to four cups per day had an approximately 25 percent lower risk than those who drank between zero and two cups per day.
In addition, in the studies that assessed decaffeinated coffee consumption, those who drank more than three to four cups per day had about a one-third lower risk of diabetes than those who drank none. Those who drank more than three to four cups of tea had a one-fifth lower risk than those who drank no tea.
That the apparent protective effect of tea and coffee consumption appears to be independent of a number of potential confounding variables raises the possibility of direct biological effects, the authors write. Because of the association between decaffeinated coffee and diabetes risk, the association is unlikely to be solely related to caffeine. Other compounds in coffee and tea including magnesium, antioxidants known as lignans or chlorogenic acids may be involved, the authors note.
If such beneficial effects were observed in interventional trials to be real, the implications for the millions of individuals who have diabetes mellitus, or who are at future risk of developing it, would be substantial, they conclude. For example, the identification of the active components of these beverages could open up therapeutic options for the primary prevention of diabetes mellitus. The findings also pose the question of whether patients most at risk for diabetes mellitus may in the future be advised to increase their consumption of tea and coffee in addition to increasing their levels of physical activity.
Spokesperson for the European Society of Cardiology, Professor Lars Rydén (Sweden), who is a diabetes specialist had the following advice: "This is a cautiously and carefully conducted meta-analysis which means authors have carefully conducted studies although each are too small to give an answer to the question although they indicate a positive correlation between the consumption of coffee and a decreasing occurrence of diabetes. So the principle is that if you drink coffee whether it is decaffeinated or not, you have less chance of developing diabetes. The data has been strengthened by bringing several studies together.
There are sometimes claims that coffee may do harm, that it may increase the propensity to Cardiovascular disease, but there is no evidence for this. The message is that people may drink coffee safely. Coffee from this point of view may actually be of benefit, as well as reducing the risk of getting diabetes – although the reduction is small (around 7%)."
However Prof Rydén warns that lifestyle changes far outweigh a regular coffee intake.
"Coffee helps, but other things are even more important. Those who are overweight should reduce their bodyweight by 5-10% - not too much - and include physical activity such as a brisk walk for 30 minutes a day. Then those people who are at risk of developing diabetes will reduce this risk by 40-50%.
It is interesting to consider why a beverage like coffee has a beneficial effect. It is obviously not the caffeine as decaffeinated coffee has the same efficiency as caffeinated coffee. Coffee may contain antioxidants but the studies have not measured the number of chemicals in the blood which is important."