I don't know if you could say I'm a heavy coffee drinker, but the most I ever drink is 3 cups a day. I regularly take tolerance breaks, however, where I'll only a few cups of green tea (ideally decaf) per day for a week or two.
For me it acts as a reliable aphrodisiac, with pro-social and pro-cognitive effects, alleviating depression, and it actually actually helps digestion in my case. I've never noticed the vision thing you mentioned, though I am without a doubt more calm and at ease when I'm well into a caffeine detox. I definitely think that drinking 3 cups of coffee a day can increase my irritability and stress as well.
I notice such a wide range of positive effects from coffee that the positives outweigh the negatives. I think it's best used once a week or so. I can't imagine ever going caffeine-free for good.
There are a few sources that indicate chronic caffeine impairs hippocampal neurogenesis...which is certainly disconcerting.
Neurogenesis continues through adulthood in the hippocampus and olfactory bulb of mammals. Adult neurogenesis has been implicated in learning and memory, and linked with depression. Hippocampal neurogenesis is increased in response to a number of stimuli, including exposure to an enriched environment, increased locomotor activity, and administration of antidepressants. Adult neurogenesis is depressed in response to aging, stress and sleep deprivation. Intriguingly, caffeine modulates a number of these same stimuli in a dose-dependent manner. We examined the dose and duration dependent effects of caffeine on the proliferation, differentiation, and survival of newly generated hippocampal neurons in adult mice. Extended, 7-day caffeine administration, alters the proliferation of adult hippocampal precursors in the mouse in a dose dependent manner; moderate to high doses (20–30mg/kg/day) of caffeine depress proliferation while supraphysiological doses (60mg/kg/day) increase proliferation of neuronal precursors. Acute, 1-day administration had no affect on proliferation. Caffeine administration does not affect the expression of early or late markers of neuronal differentiation, or rates of long-term survival. However, neurons induced in response to supraphysiological levels of caffeine have a lower survival rate than control cells; increased proliferation does not yield an increase in long-term neurogenesis. These results demonstrate that physiologically relevant doses of caffeine can significantly depress adult hippocampal neurogenesis.
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Edited by Wingless, 10 July 2016 - 03:27 PM.