I think we vary a heck of a lot in our reactions to coffee.
I find that I get a mild bump in blood pressure, and a spike of about 1mmol/l for about an hour - but I only take decaff, once a day (ish) and I take it 'cut' with double cream, which will slow things down and take the edge off.
Several things MAY be at play
- the caffeine (though 'they' say it won't)
- the decaffeinated method (there are chemicals, and there is water decaffeination - presumably, some chemicals will get a reaction. Maybe)
- the time of day
- stress levels
- other nastinesses that get into the beans (there is a school of thought that there are fungi that grow on the beans in the warehouses sometimes that leave toxins in the coffee, which cause reactions. See Mr Bulletproof Coffee for the lowdown on that, as he tries to sell you his wonderful beans...)
I certainly think I do better on single estate posh coffee beans, water decaffed, but is that my inner coffeesnobbishness, or is it real?
You asked if the spike was harmful? Really, that is hard to quantify, but it is FAR larger a spike than I would want after a full meal, and my body dislikes fast rises and falls more than it dislikes a longer, slower, sustained rise...
I suggest a period of exhaustive self testing, different brands, caff v decaff, black, milk, cream... that could keep me entertained for WEEKS!
