Studies have now shown that , when consumed in moderation, can against certain diseases and may even extend lifespan.

Studies have now shown that moderate coffee consumption might protect against cardiovascular , diabetes, and Parkinson’s , to name but three.

But the findings to date leave some unanswered questions. For instance, “moderate consumption” — which usually means three to five cups per day — depending on the study, seems to be of benefit, but many people drink six or more cups each day.

So, do they still enjoy coffee’s protective powers?

Also, certain people have genetic variations that alter the way in which they metabolize, or break down, caffeine. How are these individuals affected? Similarly, does the type of coffee — ground, instant, or decaffeinated — make a difference to health outcomes?

Other studies have attempted to answer the questions above, but, because fewer people fall into these categories, it has been difficult to make robust conclusions from the available data.

Recently, researchers at the National Cancer Institute (NCI) in Rockville and the (NIH) in Bethesda, both in Maryland, set out to get some answers.

Their work, which includes the data of more than half a million people in the United Kingdom, is published today in JAMA Internal Medicine.

The scientists found that, as predicted, coffee drinkers had a lower risk of death over the course of the follow-up. They also found that this reduction in risk extended to people who drank eight or more cups each day.

It also affected people who metabolize caffeine slower or faster than normal, and it worked across all coffee types (although the benefits were slightly less pronounced for instant coffee).

The fact that individuals who process caffeine differently and those who drink decaffeinated coffee also saw benefits hints that caffeine is not the main player in this beneficial relationship. Coffee consists of hundreds of different chemicals, making this a tricky code to crack.

One group of chemicals that scientists have been interested in is polyphenols, which are found in reduced levels in instant coffee. Much more work will be needed to understand how they fit into the bigger picture, though.

The new study is based on observational data, but because of the large number of participants used, the authors conclude:

These results provide further evidence that coffee drinking can be part of a healthy diet and may provide reassurance to those who drink coffee and enjoy it.

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