Empty‑stomach coffee triggers short‑term hormone and blood pressure shifts

Drinking a cup of coffee immediately after waking provides a brief energy boost from caffeine, lasting up to four to six hours. The stimulant also causes a temporary rise in the stress hormone cortisol, especially in people who are not regular coffee drinkers.

The caffeine can stimulate bowel movements but may also cause stomach irritation, acid reflux, gas and bloating. It interferes with the absorption of several nutrients such as calcium, magnesium, iron and vitamin D, so supplements should be taken at a different time. Blood pressure may increase briefly due to narrowed arteries, and blood‑sugar levels can rise as stored glucose is released.

Overall, the effects are short‑lived; regular moderate consumption may lessen the risks, and individuals with hypertension or nutrient deficiencies are advised to consult health professionals.