Giuseppe Grosso, a nutritional epidemiologist at the University of Catania in Italy says: “It’s impossible that we still struggle to choose if coffee is healthy or unhealthy.” Grosso and his colleagues collected all studies on the health effects of coffee, systematically reviewed the evidence to address this vexing situation, and then offered up their bottom line in the Annual Review of Nutrition. Especially, they observed 127 meta-analyses, which lump together and statistically evaluate studies on similar topics.
A few of the studies were randomized controlled trials on coffee or caffeine administration, but most were observational studies of real-world coffee and caffeine-consuming habits. The team calculated the strength of the study’s designs and conclusions for each meta-analysis and then ranked its evidence for relationships between coffee and health on a scale from “convincing” all the way down to “limited.”
No studies showed a “confirmation” level of evidence — not surprisingly since experimental studies lack the rigor of ¬gold-standard trials that use placebo controls. A coffee habit was also linked with a decreased rate of death from any cause during the course of a study. Pregnant women: the only group who should exercise caution with coffee. Some studies showed a relation between caffeine or coffee intake and increased risk of miscarriage.
Fetuses lack the enzyme needed to metabolize caffeine, and they accumulate caffeine when the mother drinks coffee, Grosso notes. The team also solved some earlier discrepancies involving coffee and the risk of high blood pressure and death from all cancers (when lumped together).
The confusion, they found, stemmed from a failure to adequately control for smoking — a habit that’s strongly linked to coffee consumption.
Many studies can’t measure exact coffee volumes or caffeine levels. Coffee lovers probably benefit from two main mechanisms.First, coffee beans contain phytochemicals that have anti¬oxidant and anti-inflammatory properties. Second, caffeine and other phyto¬chemicals have specific effects on enzymes that regulate liver function, insulin and glucose metabolism, and DNA repair.