Here at DiabetesSelfManagement.com, we’ve looked at a number of studies on coffee over the years — including ones with both positive and negative implications for diabetes. When studies contradict each other, it can be difficult to know what to believe, which is why it’s essential to take any single study with a grain of salt, and to look at as many studies on a subject as possible.
This is exactly what researchers tried to do in a recent review, looking at the effects of coffee on dozens of different health-related outcomes. To do this, they looked at the combined results of previously published studies — both observational, in which participants simply go about their normal lives and have certain outcomes measured, and interventional, in which participants are assigned to a particular behavior.
Layers of studies
The review, published in November 2017 in the journal BMJ, didn’t actually look at raw studies. Instead, it looked at previous analyses of multiple studies — known as meta-analyses — which combine data from similar studies to achieve greater confidence in the outcomes being measured. This allowed the researchers to focus on patterns across different health outcomes, rather than try to measure the effects in one specific area.
Overall, the researchers looked at 201 meta-analyses of observational studies on coffee that covered 67 different health outcomes, as well as 17 meta-analyses of interventional studies that covered 9 different health outcomes. While interventional studies are generally considered more reliable, assigning participants to drink or not drink coffee can be difficult, so it’s unclear whether this type of study is better when it comes to habits like drinking coffee.
As noted in an article on the review at MedPage Today, the researchers found mostly beneficial effects from drinking coffee, with the greatest benefits associated with drinking 3 to 4 cups of coffee daily. Among coffee drinkers, the overall risk of death was 17% lower, and high versus low consumers of coffee had an 18% lower cancer risk. Coffee was also beneficial to a number of neurologic, metabolic, and liver conditions, including nonalcoholic fatty liver disease and Alzheimer’s disease.
When it came to Type 2 diabetes, coffee was found to have a preventive effect. People with a higher level of coffee consumption were found to be 30% less likely to develop the condition than those with lower coffee consumption.
Reasons for caution?
There were, however, some notable exceptions to the health benefits generally associated with drinking coffee. One broad area in which coffee had harmful effects was pregnancy. Among women who drank the highest versus the lowest levels of coffee during pregnancy, low birth weight was 31% more common, pregnancy loss was 46% more common, and the risk of preterm birth in the first or second trimesters was increased
Another area in which coffee prompted caution was bone fractures in women, which were increased overall among the heaviest coffee drinkers. Due to the risks posed to pregnant women and those at risk for bone fractures, the researchers indicated that these groups might need to be excluded from future interventional studies of coffee.
But due to coffee’s impressive overall health and safety profile, the researchers recommended that other groups of people be included in future interventional studies of the beverage so that its precise effects on health can be better understood.
What’s your relationship with coffee — do you enjoy it daily, or multiple times each day? Have you noticed any positive or negative effects from coffee on your health, including your blood glucose levels? Would you be open to increasing or decreasing your coffee consumption if research supported a different optimum intake level for people with your health profile? Leave a comment below!