The first study to examine whether a change in the amount of tea or coffee consumed has any effect on the subsequent risk for type 2 diabetes among healthy individuals has found that it does, at least for coffee. And the effects become apparent within a relatively short period of time, 4 years.
In this new observational analysis of 3 large US cohorts, those who increased their intake by around one-and-a-half cups of regular coffee per day, on average, had an 11% lower risk for type 2 diabetes over the following 4 years, compared with people who did not alter the amount of coffee they drank, report Shilpa N. Bhupathiraju, PhD, department of nutrition, Harvard Public School of Health, Boston, Massachusetts, and colleagues in the study, published online April 24 in Diabetologia.
And conversely, those who reduced the amount of coffee drunk by a median of 2 cups per day had a 17% higher risk for type 2 diabetes during the next 4 years, relative to those who didn't change their coffee habit.
Changes in tea consumption were not associated with type 2 diabetes risk, possibly because not that many people drank tea or changed the amount of tea they drank, Dr. Bhupathiraju told Medscape Medical News.
Drink up to 6 Cups of Coffee as Part of a Healthy Diet
"Several meta-analyses have been done, and they all say the same thing: higher consumption of coffee is associated with lower risk for type 2 diabetes," Dr. Bhupathiraju explained. "What we did here, and what's novel about this study, is that we looked at actual changes in coffee and tea consumption [by study participants] and what their risk of type 2 diabetes was afterward, compared with those who didn't make any changes."
She stressed, however, "We are talking about a regular, 8-oz [240-mL] cup of coffee here; it's not those big cups of coffee or blended coffees such as cappuccinos or lattes. What we looked at was black coffee, with little or no milk or sugar."
Nevertheless, "based on available evidence — mainly from observational studies, because it's hard to do a clinical trial on dietary outcomes and type 2 diabetes — moderate coffee consumption is associated with a lower risk of several health outcomes, such as type 2 diabetes and cardiovascular disease," she observed.
To further quantify, she said that "up to 6 cups of coffee a day" seems to confer a lower risk of type 2 diabetes. "We need to see coffee drinking as part of an overall good lifestyle, [including] a healthy body weight, being physically active, and consuming a healthy diet."
Caffeinated Coffee, Not Decaf, Seems Most Important
In the new paper, Dr. Bhupathiraju and colleagues used observational data from 3 large prospective, US-based studies: 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 health professionals aged 40–75 years, 1986–2006). Detailed information on diet, lifestyle, medical conditions, and chronic diseases was collected every 2 to 4 years for over 20 years.
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 NHS II; and 27,759 men in HPFS.
There were 7269 documented cases of type 2 diabetes.
As well as the noted changes in risk for type 2 diabetes for those increasing or decreasing coffee consumption, compared with those who didn't alter intake, the researchers observed that those with the highest coffee intake who maintained that consumption — referred to as "high-stable consumers" — had the lowest risk for type 2 diabetes overall.
These participants drank 3 cups or more of caffeinated coffee per day consistently and had a 37% lower risk for diabetes than the "low-stable consumers," who downed one cup or less per day.
Dr. Bhupathiraju and colleagues also looked at decaffeinated coffee separately. While baseline decaffeinated coffee consumption was associated with a lower type 2 diabetes risk, alterations in decaffeinated coffee consumption did not change this.
But Dr. Bhupathiraju pointed out that, as with tea, "consumption of decaffeinated coffee was low to begin with, and there wasn't a substantial population of the patients who made changes."
Large Study With Long Follow-Up Gives Novel Evidence
The higher risk for type 2 diabetes associated with reducing coffee intake may represent a true change in risk, say the authors, or may potentially be due to reverse causation, whereby those with medical conditions associated with risk for type 2 diabetes, such as hypertension, hypercholesterolemia, or cancer, may reduce their coffee consumption after diagnosis. But even when cases of cardiovascular disease or cancer were excluded during follow-up, the results were very similar.
"Changes in coffee-consumption habits appear to affect diabetes risk in a relatively short amount of time…in these 3 large prospective cohorts with more than 1.6 million person-years of follow-up," the researchers conclude.
"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."
Dr. Bhupathiraju reports no relevant financial relationships. Disclosures for the authors are listed in the article.
Diabetologia. Published online April 24, 2014.
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Cite this: Upping Coffee Consumption Protects Against Type 2 Diabetes - Medscape - Apr 24, 2014.