It's like with everything, moderation is the key for anything. A lot of thing are good for our health but can be health threatening if you abuse them. We all have level of arsenic, iron, mercury in our body that are essential for a good health, but in high doses can be harmful or deadly. I took metallic mollecule, because the overdose is a very small quantity and demonstrate well the concept of good in right measure and harmful when abused.
Coffee is not as harmful of course if you abuse it, I believe it would be very hard to consume enough caffeine from coffee at a point to be life threatening. Unless if you are already having a health issue (cardiac ...), chronic inflammatory issue; such as people suffering; ezcema, psoriasis, fibromialgy, caffeine stimulate the immune system and can worsen the condition of people suffering these sickness. On the other end, coffee is very helpful to people suffering asthma (improve blood circulation and oxygen flow), preventing sickness by stimulating the immune system and so on.
So mostly coffee is harmless and even beneficial, but can contribute to amplify other health issue.
But just like other pinpointed, eating too acids or abusing coffee could make your digestive system more sensible.
Myself, I had to use anti-inflammatory, which are very acids, for years, (much more harmful than coffee) and it messed up with my digestive system and now I'm very sensible to any unbalance. So if my coffee is too acids, I will feel it right away and it will gives me diarhea, heartburn and stomach ache. I'm hyper sensible so just a little is enough to make me react. For a normal person, the symptom would be similar but it would require much higher dose to cause the symptom over a period of time. anti-inflammatory are advice to be consumed with food or after eating because alone they are too acids for the stomach and harmful. The same apply to coffee, eat with your coffeee and your stomach will feel much better.
If you have digestive system sensibility like me, I would recommend to try good quality of coffee that show propriety of low acidicty and low cafeine level. *it is not exactly the cafeine alone that wake you up by the way, but a mixte of compound that coffee have.*
Some vitamins like B12, D have waking up property and help for concentration. If you come from a country with a winter, you are probably vitamins D deficient as well and can cause many small issue like higher level of stress, lack of energy, tireness. That higher level of stress can cause digestive issue, small inflammation and so on. If you feel tired in the winter, try to take a multi vitamins and a complement of vitamin D. (vitamin D alone is not well assimiliated by the body and it requires vitamins B complex and some other to be absorbed efficiently). The sun is the best provider of vitamin D and has everything your body needs to absorb it, so if you come from a sunny country, this doesn't apply to you.
I was maybe a bit out of topic and over sharing, but just so you know, I'm a very rational individual and I don't believe in homeopathy or 100% natural treatment because medication is said to be so evil ... Everything I just shared is verified information and I experienced it personally with my health condition.
