Caffeine can have both positive and negative effects on the body. For example, tea and coffee will improve mental alertness and might help to reduce the risk of Parkinson’s disease and atherosclerosis, according to MedLine Plus. There’s also a dark side to caffeine, though. Not everybody reacts the same way to it and some people might have more serious side effects than others, even if they’re drinking the same amount of tea and coffee.

Increased Heart Rate

Both tea and coffee can increase heart rate and blood pressure. As heart rate increases, the flow of blood to the heart increases and the flow of blood to the brain decreases. This means that you might feel foggy and tired as you come down from a caffeine “high,” which can happen minutes to hours after drinking coffee.

Anxiety

According to the Diabetes Mellitus Information website, caffeine increases the production of adrenaline and cortisol, the stress hormones. This can result in heightened senses but will also put you on edge, elevate your stress levels and might cause anxiety.

Elevated Blood Sugar

Caffeine can affect blood glucose, according to MedLine Plus. When you drink caffeine, your blood sugar spikes. As you come down from the “caffeine high,” your blood sugar plummets. These sudden changes in blood sugar can be dangerous for people with diabetes.

Increased Risk of Osteoporosis

According to MedLine Plus, caffeine can increase the loss of calcium. When you consume lots of caffeine, your body has trouble absorbing the calcium you get from your diet. Instead, much of it is immediately lost in the urine. This can lead to weak bones and osteoporosis later on in life.