Most people drinking three or four cups of coffee a day are within safe limits. The problems tend to come from timing and from drinks whose caffeine content is easy to underestimate.
Chowdhury Tasneem Hasin, chief clinical dietitian and head of the dietetics and nutrition department at Continental Hospital PLC, puts the ceiling for healthy adults at 350 to 400mg a day, roughly four small cups of coffee. Pregnant and breastfeeding women should stay at half that, 175 to 200mg. Children under two should have none at all, and those aged eight to twelve should stay under 100mg.
Knowing where you stand requires knowing what is in the cup. A cup of regular coffee carries about 100mg. Instant coffee is lower at 50 to 60mg, and an espresso shot around 70mg. Black tea contributes 47 to 50mg a cup, and a can of caffeinated soft drink about 40mg. Tea and soft drinks are where people most often lose track, because neither feels like a caffeine delivery system in the way coffee does.
There are benefits on the other side of the ledger. Caffeine triggers dopamine and norepinephrine, which is the mood lift people notice. Coffee and tea also contain polyphenols, and there is evidence associating caffeine intake with reduced effects of Parkinson’s and Alzheimer’s disease.
Past the limit, the costs are familiar: stomach upset, headaches, anxiety, a raised heart rate and jitters. Caffeine is also a diuretic, so heavy consumption contributes to dehydration. The brain develops dependence quite readily, which is why cutting back abruptly produces headaches.
On timing, Hasin recommends the last dose of the day by four or five in the afternoon, or before sunset. Caffeine’s half-life means an evening cup is still circulating at bedtime even when it does not feel like it.
Meals deserve a mention too, for a reason most people have never been told. Tannins interfere with how much iron the body takes up from food, so the cup is better placed 40 to 60 minutes after eating than alongside it. Anyone watching their iron levels should take that seriously; everyone else can file it as a small improvement.
On weight, caffeine does raise metabolic rate, but not enough to matter on its own. Losing weight still requires a calorie deficit, and coffee is a marginal contributor rather than a mechanism.
