Coffee

Coffee is the largest dietary source of caffeine and polyphenols (chlorogenic acids) for most American adults. The cardiovascular evidence has flipped over the last twenty years from cautious-to-positive: large meta-analyses now show 3-4 cups a day is associated with lower all-cause mortality and reduced risk of type 2 diabetes, Parkinson's, and certain liver cancers. The effect size is modest and the confounding considerable, but the direction is consistent.

Sleep and anxiety

Caffeine has a half-life of around 5 hours in most adults, longer in slow metabolizers (CYP1A2 genetics) and during pregnancy. Coffee after about 2pm pushes detectable caffeine into bedtime for many people and measurably reduces deep sleep even when people don't feel "wired." For anxiety-prone people, caffeine amplifies sympathetic nervous system activity — the racing heart and edge are real, not psychosomatic.

Reflux and gut

Coffee relaxes the lower esophageal sphincter and stimulates acid secretion — a frequent reflux trigger independent of caffeine (decaf does the same). The chlorogenic acids and N-methylpyridinium produced during roasting are the suspected mediators; low-acid coffees (longer roasts, cold brew, certain origins) are sometimes better tolerated. Coffee also stimulates colonic motility, which is why the morning bowel movement is reliable for many drinkers.

Filtering matters for cholesterol. Unfiltered coffee (French press, espresso, Turkish, boiled) contains cafestol and kahweol — compounds that measurably raise LDL. Paper-filtered drip coffee removes most of them. For someone with a borderline lipid panel, switching from French press to filtered is a small but real lever.