Coffee's effects come from three compound groups pulling different ways. The stimulant group sharpens physical output and attention within an hour, and shortens sleep when present at bedtime. The oily group raises blood cholesterol unless a paper filter removes it. The plant-acid group tracks lower diabetes, liver scarring and liver cancer. Brewing method, timing and biology matter more than quantity. (Full Review)
| Marker | Target | Why |
|---|---|---|
| LDL cholesterol | <100 mg/dL; <70 mg/dL if cardiovascular risk elevated | Detects the diterpene effect of unfiltered brewing |
| Apolipoprotein B | <80 mg/dL; <60 mg/dL if risk elevated | More reliable than LDL when triglycerides are high |
| Triglycerides | <80 mg/dL | Rises alongside cholesterol on unfiltered coffee |
| Seated resting blood pressure | <120/80 mmHg | Captures the sustained rise and acute reactivity |
| HbA1c | 4.8–5.4% | Tracks the metabolic association behind habitual intake |
| Fasting insulin | 2–6 µIU/mL | More sensitive than HbA1c to early insulin resistance |
| ALT | <25 U/L men, <20 U/L women | The most consistent organ-specific benefit signal |
| GGT | <25 U/L | Falls with habitual coffee intake and tracks liver fat |
| eGFR | >90 mL/min/1.73 m² | Kidney association unresolved; personal trend is the useful signal |
| Ferritin | 50–150 ng/mL in women, 50–200 ng/mL in men | Coffee with meals substantially reduces iron absorption |
| Intraocular pressure | 10–21 mmHg | Caffeine raises it in glaucoma and ocular hypertension |
| Total sleep time and sleep efficiency | ≥7 hours; efficiency ≥85% | The most consistent cost of caffeine, and the easiest to move |
| Resting heart rate and heart-rate variability | No coffee-specific target; change from own two-week baseline | Detects excess sympathetic load from over-shooting the dose |
Cadence: Lipid panel and blood pressure 8 weeks after any change in brewing method or dose, then annually; HbA1c, liver enzymes and kidney filtration every 12 months; ferritin every 6–12 months if iron status was borderline; eye pressure on the ophthalmologist's schedule.