Fill in the blanks with an appropriate verb form.

Caffeine ……………. (works / is working / has worked) by blocking the effects of Adenosine, a sleep-inducing substance …………… (produce / produced / producing) by your body. The substance ………….. (has accumulated / accumulates / is accumulating) inside you throughout the day. As adenosine levels ………………. (rise / rose / risen), you become calm and drowsy. Later, as you sleep, adenosine levels ………….. (drop / has dropped / dropped). When you wake up, the cycle …………. (start / starts / started) again. By not allowing adenosine to build up, caffeine ……………. (keep / keeps / has kept) you feeling fired up.

Caffeine also …………….. (increase / increases / has increased) your blood pressure, which may make you feel as if your chest is pounding. Research …………… (has shown / showed / show) that caffeine …………….. (interfered / interferes / had interfered) with the body’s ability to process sugars, which may lead to a disease called type 2 diabetes. A can of caffeinated cola every now and then is probably OK, nutritionists say, but sip carefully!

Answers

Caffeine works by blocking the effects of the sleep-inducing substance adenosine, produced by your body. The substance accumulates inside you throughout the day. As adenosine levels rise, you become calm and drowsy. Later, as you sleep, adenosine levels drop. When you wake up, the cycle starts again. By not allowing adenosine to build up, caffeine keeps you feeling fired up.

Caffeine also increases your blood pressure, which may make you feel as if your chest is pounding. Research has shown that caffeine interferes with the body’s ability to process sugars, which may lead to a disease called type 2 diabetes. A can of caffeinated cola every now and then is probably OK, nutritionists say, but sip carefully!