Caffeine supplements nudged blood pressure up by about 2 mmHg
Pooled across eight placebo-controlled trials, caffeine left blood pressure about 2 mmHg higher, more so in men, at higher doses and in trials past nine weeks.
What the study found
Caffeine supplements left blood pressure about 2 mmHg above placebo
Across eight trials of caffeine against placebo or control, adults' blood pressure ended about 2 mmHg higher: 1.94 systolic and 1.66 diastolic. The rise was bigger in men and grew with dose, and in trials longer than nine weeks it was larger, not smaller.
The caveat · Caffeine itself, not coffee
The trials gave caffeine itself, not coffee, at doses and for lengths that varied from trial to trial. Eight trials is a small base to split by sex, dose and length, so those three patterns are leads rather than settled findings. The clearest dose effect, above 400 mg a day, was in diastolic pressure.