Green tea is one of the oldest herbal teas known to man. It gained quick prominence in the West because of its purported health benefits, weight loss being one of the popular ones. Some of these health benefits are backed by studies, while some still need to be researched. But one needs to be aware of the side effects as well.
Green tea is mostly safe for adults when consumed in moderation. Green tea extract is also considered to be generally safe for most people when taken orally or applied topically on the skin for a short period of time. However, drinking too much green tea (more than 5 cups a day) is considered to be unsafe.
Side Effects Of Green Tea
Like all teas, green tea contains caffeine; excessive caffeine intake can lead to or aggravate a variety of problems, including the following:
1. Stomach Problems
The tannins present in green tea increase stomach acidity that may cause stomach ache, nausea, or constipation. For this reason, green tea is not consumed on an empty stomach in Japan and China.
A study on dietary supplementation with green tea extracts found that green tea supplement on an empty stomach can affect the liver.
It is best to drink green tea after a meal or between meals. People with peptic ulcers or acid reflux should not consume green tea excessively. A 1984 study concluded that tea is a potent stimulant of gastric acid, which can be reduced by adding milk and sugar.
Sometimes, improper brewing of green tea may also have adverse effects. Green tea is best brewed with water between 160° and 280° F. Excessively hot water may cause heartburn or an upset stomach.
2. Iron Deficiency and Anemia
Green tea reduces the absorption of iron from food. Its polyphenols bind to the iron and make it less available to your body. It was previously believed that green tea hindered the absorption of non-heme iron (iron from animal sources) by about 25%. But recent findings suggest that it hinders heme or plant iron absorption too.
However, vitamin C increases non-heme iron absorption, so you can squeeze lemon into your tea or consume other vitamin-C rich foods such as peas, broccoli, and tomatoes with your meal. If you have an iron deficiency like anemia, the National Cancer Institute recommends consuming tea between meals.
3. Mild To Serious Headaches
While green tea is considered a safe beverage for migraine patients, it might still be off the diet chart for people with chronic daily headaches. Population-based research studies have shown that caffeine is a risk factor for chronic daily headache onset, and though green tea contains much less caffeine than coffee or other kinds of tea, it is best avoided by such people.
4. Sleep Problems, Nervousness, And Anxiety
No matter how little caffeine green tea contains, it is not a bedtime drink. Caffeine itself can block sleep-inducing chemicals in the brain and increase adrenaline production. Caffeine exerts obvious effects on anxiety and sleep, which vary according to your sensitivity to it.
Green tea also contains the amino acid L-theanine, which has the capacity to calm you down but also make you alert and focus and concentrate better, which is at odds with getting a good night’s sleep.
5. Irregular or Accelerated Heartbeat
Caffeine in green tea might cause an irregular heartbeat. It also stimulates the heart muscles to contract when at rest.
Because caffeine affects the movement of food through the food pipe, alternating contraction and relaxation of the food pipe muscles can cause nausea.
Caffeine has a laxative effect. It contributes to peristalsis (the movement of food through the digestive system). It stimulates the colon muscles to contract and then relax, which results in an increased need to move your bowels.
8. Muscle Tremors and Contractions
By regulating calcium ion channels within cells, caffeine forces skeletal muscle contractions.
Caffeine increases the release of acid in your stomach. This causes discomfort similar to heartburn.
Caffeine can decrease the flow of blood to the brain, leading to dizziness and motion sickness.
11. Ringing in the Ears
Caffeine can aggravate tinnitus or ringing in the ears.
Caffeine stimulates the central nervous system. It activates neurons when consumed in excess, thus, causing convulsions.
13. Bleeding Disorders
Caffeine in green tea might increase the risk of bleeding.
Caffeine in green tea might interfere with blood sugar control. If you drink green tea and have diabetes, monitor your blood sugar carefully.
Drinking green tea increases pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes.
16. High Blood Pressure
The caffeine in green tea might increase blood pressure in people with high blood pressure. However, this does not seem to occur in people who regularly drink green tea or other products that contain caffeine.
17. Liver Disease
Green tea extract supplements have been linked to several cases of liver damage. Green tea extracts might worsen liver disease as the caffeine in the blood may build up and last longer.
Drinking green tea can increase the amount of calcium that is flushed out in urine, which can lead to deterioration of bone health and osteoporosis, especially in those who might be predisposed to the same due to other factors. Caffeine should be limited to less than 300 mg per day (approximately 2-3 cups of green tea). It is possible to make up for some calcium loss caused by caffeine by ingesting calcium supplements.
19. Pregnancy and Infant Health Risks
Green tea contains caffeine, catechins, and tannic acids. All three substances have been linked to pregnancy risks. If you are pregnant or breastfeeding, green tea in small amounts – about 2 cups per day – is safe. This amount of green tea provides about 200 mg of caffeine. However, drinking more than 2 cups of green tea per day has been linked to an increased risk of miscarriage and other negative effects.
Caffeine passes into breast milk and can affect a nursing infant. In addition, drinking a large amount may cause neural tube birth defect in babies.
20. Nutrient Absorption Problems in Children
The tannins in green tea may block nutrients absorption such as protein and fats in children. It may also lead to overstimulation because of the caffeine present in green tea.
Can People On Medication Drink Green Tea?
Green tea must not be taken along with these medications as it is known to cause negative reactions:
Stimulant drugs like Amphetamines, Nicotine, Cocaine and Ephedrine.
Adenosine, Quinolone antibiotics, Birth control pills, Cimetidine (Tagamet), Clozapine (Clozaril), Dipyridamole (Persantine), Disulfiram (Antabuse), Estrogens pills, Fluvoxamine (Luvox), Lithium, Medications for depression (MAOIs), Hepatotoxic drugs, Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs), Pentobarbital (Nembutal), Phenylpropanolamin, Riluzole (Rilutek),Theophylline, Verapamil and Warfarin.
Alcohol, Fluconazole, Anti-diabetes drugs, Mexiletine (Mexitil) and Terbinafine.
You don’t have to quit drinking your favourite cup of green tea, but if you have any of the above mentioned medical conditions or taking prescription drugs, exercise caution and consult your doctor about how many cups you can have per day. Moderation is the key to enjoying the full benefits of green tea.