Iced Americano, commonly called "a-a" in Korea, is considered a must-have for office workers. It is widely perceived as easy to drink without concern, as it contains almost no calories or sugar. But an expert has warned that black coffee, made without sugar or syrup, can still raise blood sugar in some people.
According to the medical community on the 25th, Professor Ahn Chul-woo of the Department of Endocrinology at Gangnam Severance Hospital, who runs the YouTube channel "Ahn Chul-woo's Hormone TV," warned that "even black coffee without sugar or syrup can be a cause of rising blood sugar for some people."
"More people than you might think ask, 'Why does my blood sugar rise when I only drink black iced Americano without sugar in my coffee?'" Ahn said. "The fact that blood sugar rises after drinking black coffee does not mean the coffee contains a lot of sugar. Rather than the sugar in coffee, you need to look at how your body reacts to caffeine."
When caffeine enters the body, secretion of the stress hormones cortisol and adrenaline can increase. The body interprets this as a situation requiring energy and releases glucose stored in the liver into the bloodstream. This is why blood sugar can rise even without eating sweet foods.
In the morning, cortisol levels naturally rise during the process of waking up. Drinking coffee on an empty stomach at this time can cause greater blood sugar fluctuations in some people.
Coffee consumed in the afternoon or evening can also disrupt sleep, affecting the next day's fasting blood sugar.
"When sleep quality declines due to caffeine, secretion of the sleep hormone melatonin decreases," Ahn said. "Melatonin plays an important role in stably lowering fasting blood sugar overnight, and as this hormone decreases, fasting blood sugar rises the next morning after a night of poor sleep."
Decaffeinated coffee may also contain small amounts of caffeine. Adding milk, syrup, or powder can directly raise blood sugar due to the sugars and carbohydrates they contain.
"Even with decaffeinated coffee, if you add milk, syrup, or powder, the lactose and carbohydrates they contain directly raise blood sugar, so caution is needed," Ahn advised.
The more shots added, the greater the caffeine intake. People who need to control their blood sugar or are sensitive to caffeine should reduce the number of shots and the volume of their drink.
Coffee before exercise is not unconditionally good for blood sugar either. "There is talk that drinking coffee before exercise is good for blood sugar, but it's half true and half something to be careful about," Ahn noted. "Caffeine can help with exercise performance and alertness, but if you drink strong coffee on an empty stomach and immediately do high-intensity exercise, stress hormones can become excessive and actually raise blood sugar, so caution is needed."
To reduce blood sugar fluctuations, it is better to avoid coffee on an empty stomach and, if possible, drink it after meals. Additives such as syrup and condensed milk should be excluded, and caffeine intake should be reduced in the late afternoon.
Measuring blood sugar before drinking coffee and one to two hours afterward to check your own response is another method. The recommended daily caffeine limit for adults is 400mg or less, but sensitive individuals may experience blood sugar changes or insomnia even with smaller amounts.
