TLDR
Drinking coffee in normal amounts is safe for most people and may help lower the risk of several diseases, but pregnant women and women at risk of bone fractures should be careful.
Summary
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1 Study Aim
The main aim of this paper is to systematically review and evaluate all existing meta-analyses that examine the links between coffee drinking and a wide range of health outcomes. The authors want to understand both the possible benefits and harms of coffee consumption, and to see if there is enough evidence to support future studies where coffee is used as a health intervention. The study set out to find out if drinking coffee is good or bad for health overall.
2 Study Design
The authors conducted an umbrella review, which means they gathered and analyzed data from many published meta-analyses (studies that combine results from multiple research papers) about coffee consumption and health. They searched four major scientific databases up to July 2017 for meta-analyses that looked at coffee drinking and any health outcome in adults. Both observational studies (which observe people’s habits and health) and randomized controlled trials (where people are assigned to drink coffee or not) were included if they had a meta-analysis. The quality of each meta-analysis was checked using AMSTAR (a tool for rating systematic reviews), and the strength of the evidence was rated using GRADE (a system that ranks evidence as high, moderate, low, or very low quality). The researchers combined results from many previous studies to see how coffee drinking affects health.
3 Findings
The review found that coffee drinking is more often linked to health benefits than harms. Drinking three to four cups a day was associated with the biggest reduction in risk for several conditions, including death from any cause, heart disease, some cancers, type 2 diabetes, liver disease, Parkinson’s disease, and depression. Coffee also seemed to lower the risk of liver problems and metabolic diseases. However, drinking coffee during pregnancy was linked to higher risks of low birth weight, pregnancy loss, and childhood leukemia. Women who drink a lot of coffee may have a higher risk of bone fractures, while men may have a lower risk. Most of the evidence comes from observational studies, which means it cannot prove that coffee causes these effects. The quality of evidence was mostly low or very low. The authors recommend that future randomized controlled trials are needed, especially for people with liver disease, but these trials should avoid including pregnant women or women at high risk of fractures. Drinking coffee seems safe for most people and may help prevent some diseases, but pregnant women and some women should be careful.