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 current edition of 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.
Cup of coffee
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.
Cup of coffee
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!”
Other authors of the study included Brian Chen, of UCLA, and Julie Buring, JoAnn Manson and Yiqing Song, of Brigham and Women’s Hospital and Harvard Medical School. Funding was provided by the National Institutes of Health. No conflicts of interest were reported by the authors.
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A new study has suggested that simply taking more steps every day not only helps ward off obesity but also reduces the risk of diabetes.
While previous studies have shown that physical activity reduces body mass index and insulin resistance – an early stage in the development of diabetes – this is the first study to estimate the effects of long-term changes in daily step count on insulin sensitivity.
A popular guideline is to do 10,000 steps every day, though a more recent recommendation is 3,000 steps, five days a week.
The study, by the Murdoch Childrens Research Institute, Melbourne, involved 592 middle aged adults who took part in a national study to map diabetes levels across Australia between 2000 and 2005.
At the start of the study, participants completed a detailed diet and lifestyle questionnaire and underwent a thorough health examination. They were also given a pedometer and instructed how to use it. Participants were monitored again five years later.
Other lifestyle factors, such as diet, alcohol and smoking were taken into account.
A higher daily step count over five years was associated with a lower body mass index, lower waist to hip ratio, and better insulin sensitivity.
These associations were independent of dietary energy intake and appeared to be largely due to a change in adiposity (fatness) over the five years, say the authors.
The authors estimate that, in their setting, a sedentary person who takes a very low number of daily steps but who was able to change behaviour over five years to meet the popular 10,000 daily step guideline would have a threefold improvement in insulin sensitivity compared with a similar person who increased his or her steps to meet the more recent recommendation of 3,000 steps for five days a week.
They conclude: “These findings, confirming an independent beneficial role of higher daily step count on body mass index, waist to hip ratio, and insulin sensitivity, provide further support to promote higher physical activity levels among middle aged adults.”
The study has been published on bmj.com today.
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 issue of Archives of Internal Medicine, JAMA.
By the year 2025, approximately 380 million individuals worldwide will be affected by type 2 diabetes.
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 new 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.”
Dr. Huxley is supported by a Career Development Award from the National Heart Foundation of Australia. This work was additionally supported by a grant from the National Health and Medical Research Council of Australia; a Research Career Development Fellowship from the UK Wellcome Trust; and a research grant from Institut Servier, France and Assistance Publique-Hopitaux de Paris.