One day, a study tells you to drink more coffee for your health. A couple months later, another study says coffee is bad for you. Months after that, another study says coffee is good for you, but only if you have two cups or less per day.
Research can be a constant cycle of new discoveries and contradictions. The latest coffee study, published in January by Stanford Medicine, found caffeine consumption counters health problems related to advancing age, such as systemic inflammation and cardiovascular disease. In the early 2000s and earlier, many studies showed the opposite – researchers thought coffee drinkers were likely to die at earlier ages than non-coffee drinkers.
The turning point, according to Medical News Today, was a massive Harvard-led study published in 2008 that examined data on 130,000 participants over a span of 20 years. It was the first study to find “normal” coffee drinking habits – up to six cups per day – was not linked to increased deaths in either gender, and actually could prevent heart disease.
“Earlier studies didn’t always take into account that known high-risk behaviors, such as smoking and physical inactivity, tended to be more common among heavy coffee drinkers at that time,” Donald Hensrud, a Mayo Clinic preventive medicine specialist, told Medical News Today.
Since then, other studies have found drinking coffee has numerous benefits, including reducing the risks of certain cancers (liver, mouth and throat), improving long-term memory, reducing the risk for suicide, increasing longevity and preventing Parkinson’s disease, type 2 diabetes, cardiovascular diseases and strokes.
There have been concerns that coffee consumption causes chronic kidney disease, but a study published in the International Journal of Clinical Practice in 2016 found it is not linked in men and that further research was needed to determine that risk in women. Another study published in 2017 found no link between caffeine intake and decreased male fertility.
However, the Mayo Clinic cautions that – like most things – coffee is best in moderation, and most studies promoting its potentially healthy benefits are focused on adults only. Mayo Clinic staff write that children should not drink coffee, adolescents should be limited to one cup per day at most and adults should keep it to four cups per day or less. Other medical professionals say those who are pregnant or have anxiety should limit their caffeine intake more than the average person.
Drinking more than four cups of coffee per day in typical adults can lead to insomnia, nervousness, irritability, muscle tremors, upset stomach and a fast heartbeat, according to the Mayo Clinic.
For pregnant women, drinking even two to three cups of coffee per day has been linked to low-birth weight babies, according to a study published in BMC Medicine.