Oolong Tea Health Benefits and Side Effects

Written by: Christopher Karam | ✔️ Medically Reviewed by: Dr. Riad M., M.D - G.P and Micheal B., M.D | Last Updated: 2020 April 27

Oolong tea makes up about 2% of the total amount of tea produced in the world, with China and Taiwan being the leading consumers.

There are a lot of health benefits of drinking oolong tea that improves cardiovascular, mental, muscular, and even bone health. Herbal teas are highly recommended due to their excellent health-boosting properties.

Regular tea consumption can help those suffering from type 2 diabetes, people with elevated bad (LDL) cholesterol levels, and who’re at risk of heart disease.

pouring white oolong tea into cups

It combines ingredients from green, dark, and herbal teas, giving it many health benefits such as reducing stress, blood pressure, boosting metabolism, weight loss, promoting heart health, improving bone mineral density, and improving your overall mood.

It was originally produced at the Wuyi Mountain, using the Anxi tea plantation. Discovered by a man named Wulong, the name was eventually translated to oolong.

There is more than one version of oolong tea, which is great for people who’re looking for variety. Making these a great option for people who like hot or iced teas.

All of the different types of oolong tea colors and variations will have slightly different health benefits as well as a different taste and aroma. Here is the full list of the different types of black and oolong tea variations:

  • Black Dragon Tea

  • Iron Goddess of Mercy Tea

  • Jade Oolong Tea

  • Oolong Chai Tea

  • White Oolong Tea

  • Kuan Yin Tea

  • Black Tea

  • Chai Tea

  • Oolong Matcha Tea

These traditional Chinese tea leaves are grown in the Wuyi Mountains of northern Fujian Province.

One of the best parts of loose leaf oolong tea is its sweet, soft smelling, and prominent aroma. Oolong tea’s wonderful smell slightly differs based on the variation and processes used to harvest and make it.

Some can have a floral taste and scent, while others will be slightly more fruity and sweet; especially the ones infused with peaches, berries, and other fruits.

The rest have a roasted and thicker type of fragrance and their colors can range from light green to dark brown.

Black-colored oolong tea leaves are caused by the process of fermentation, which is what gives black oolong tea it's distinct color and smell. If loose leaf oolong tea leaves are partially or lightly oxidized, they will be slightly greener and have a lighter flavor profile.

Because oolong's made from the Camellia sinensis plant, you can either make a type of oolong tea or green tea depending on how its produced and time of cultivation.

When making an oolong tea, it has to oxidize. The longer you let it oxidize, the darker the leaves get and the flavor becomes much more concentrated.

Green tea leaves are made with barely any oxidation, even the ones that are semi-oxidized have a different taste and fragrance.

After being separated from the plant, the buds start to turn black and become semi-oxidized over time.

oolong tea with tea herbs

Due to the increased oxidation, catechins levels decrease while theaflavins and thearubigins increase. Loose leaf tea plants are always green in color while they’re still attached and growing.

Black oolong tea is a darker alteration made by exposing the Camellia sinensis plants to an oxygen-rich environment to increase the rate of oxidation. Semi-oxidized teas are the best sources of antioxidants and polyphenols for maintaining proper health.

Black-colored type of oolong leaves are caused by the process of fermentation, which is what gives black oolong tea it's distinct color and smell. If loose leaf oolong tea leaves are partially or lightly oxidized, they will be slightly greener and have a lighter flavor profile.

The fermentation process is what gives the black version of oolong tea the richer and more woodsy aroma. The chemical composition of green and black oolong tea is mostly made up of polyphenols, minerals, and caffeine.

It also contains the amino acid theanine, which is what gives the tea its calming and relaxing effect.

The chemical composition of green and black oolong tea is mostly made up of polyphenols, minerals, and caffeine. Similar to tea, coffee has the highest concentration of caffeine that many people use to boost energy levels and avoid drowsiness.

It also contains the amino acid theanine, which is what gives the tea its calming and relaxing effect. Additionally, oolong tea is loaded with nutrition, one cup of brewed tea has:

  • Caffeine: 22 mg

  • Sodium: 4 mg (1% of the Recommended Daily Intake (RDA))

  • Fluoride: 1 mg (18% of the RDI)

  • Theobromine: 2.66 mg

  • Manganese: 0.28 mg (15% of the RDI)

  • Niacin: 0.09 mg (< 1% of the RDI)

  • Magnesium: 1.34 mg (< 1% of the RDI)

  • Potassium: 16 mg (< 1% of the RDI)

camellia sinensis leaves on basket

Oolong Tea Health Benefits

One of the main health benefits of oolong tea is its huge variety of flavors and scents to pick from. Oolong tea can be either earthy or a subtly fruity type of tea, covering the whole spectrum.

What's responsible for the many oolong tea health benefits are all of the antioxidants, known as tea polyphenols, theaflavins, thearubigins, and EGCGs.

1. Improves Overall Lung Health

Another health benefit of consuming oolong tea is the complete boost to your lung health.

Theophylline is the main compound associated with treating various lung diseases, infections, complications, as well as clearing the breathing passage.

It’s even used in many different medicines, theophylline can help prevent and treat:

  • Shortness of breath

  • Wheezing

  • Relieve symptoms of Asthma

  • Chronic Bronchitis

  • Chest tightness

  • Emphysema

  • and other lung diseases and complications

Oolong tea is not a replacement for prescribed medication, always consult your health care professional before making significant changes to your diet.

2. Helps Control Blood Sugar Levels and Hypoglycemia

Type 2 diabetes is a debilitating disease that is caused when your blood sugar or blood glucose is too high. Many claims state that the negative effects can be alleviated by taking advantage of the benefits of drinking oolong tea.

Oolong tea also reduces fructosamine levels and plasma glucose. Semi-oxidized teas such as green tea and oolong tea, these can reduce liver, serum lipids, and enhance insulin activity.

A recent study shows that consuming 1500 milligrams of a matcha oolong tea daily for one month has helped people correct their blood sugar levels.

The antihyperglycemic effect of oolong tea significantly reduced the plasma glucose levels (blood sugar) in the tested subjects. Drinking oolong helps manage the symptoms of diabetes, reduces hypertension, which is why it’s highly recommended for most diabetics.

Since reducing blood sugar levels in your bloodstream is the main goal for people suffering from high glucose or Type 2 diabetes, drinking just one cup of oolong tea per day can help lower and minimize the disease.

oolong tea cup on table cloth with leaves

3. Increases Metabolism And Helps With Weight Loss

The more plant compounds such as polyphenols, catechins, and EGCG levels there are in your tea, the more effective it’ll be for weight loss.

Polyphenols help boost your metabolism and decrease the volume of fat your body absorbs from your diet. They activate enzymes that encourage the use of stored body fat, stimulating fat oxidation.

In the debate between white tea vs black tea, being most effective for fat loss, the only major difference is the total amount of antioxidants. They both have similar weight loss effects.

Due to the amount of oxidation required to enhance the color and flavor of the oolong tea leaves, there’s a huge loss of nutrients that comes with that process.

Multiple studies show that regular consumption of black and greener colored teas helped subjects lose a substantial amount of fat because of the increased metabolism.

Green oolong tea is the most effective out of all herbal teas. Although, it requires 3 cups a day to see any impactful results for fat loss.

4. Improves Bone Mineral Density and Tooth Strength

Oolong tea’s antioxidants strengthen your teeth, bones, and your complete skeletal structure. Preventing disorders like osteoporosis, and reducing your risk of fractures.

Multiple long-term studies concluded that black, green, and oolong tea helped increase bone mineral density by over 2%, reduced bone mass loss, and maintained that effect for over a decade.

Additionally, oolong tea is a good source of fluoride, it also helps improve gum health, reduce tooth plaques, and strengthens tooth enamel.

This benefit also comes in handy for women who are in their menopause stages.

Menopause and postmenopausal women both have weaker bones during, which could result in arthritis and osteoporosis, oolong tea helps minimize these negative effects.

5. Treats Skin Infections, Conditions, and Eczema

Oolong tea comes in handy for people suffering from a variety of skin complications. Because it contains antioxidants, that help eliminate free radicals found in the body.

DNA damage and oxidation is the main cause of a lot of common and severe skin diseases and issues.

Semi-oxidized teas exfoliate and slow down cell oxidation, ensuring healthier skin and having anti-ageing health benefits. Some of the health benefits of oolong help treat and reduce wrinkles, dark spots, and symptoms of eczema.

The herbal tea polyphenols found in oolong tea are known to be incredible anti-allergenic compound, which helps in treating severe skin complications and irritation.

Consuming semi-oxidized teas regularly can considerably help reduce the appearance of eczema. The most common type of eczema it helps relieves is called atopic dermatitis, which is very difficult to fully cure.

One study asked 118 patients with severe cases of eczema to drink 1 Liter (33 oz) of oolong tea per day, in addition to maintaining normal treatments.

Their eczema symptoms improved as early as 1 to 2 weeks into the study. And after 1 month of the combined treatment, 63% of patients showed various improvements that were maintained. Which was still observed in over 53% of the patients 5 months later.

camellia sinensis plant field

6. Oolong Tea Boosts Cognitive Brain Function

Recent clinical studies show that oolong tea helps maintain brain functioning and performance, as well as prevent or offset symptoms of Alzheimer's disease.

Further research shows that L-theanine, an amino acid in tea, may also help boost attention, relieve anxiety, and induce calmness.

Many components of oolong tea benefits brain function, rise in attention levels, calmness, alertness, and visual information processing and performance.

Consuming caffeine can increase the release of norepinephrine and dopamine. These two neural transmitters benefit your mood, as well as increase attention and brain synapse firing functioning.

A recent study reported that consuming teas containing both caffeine and theanine increased alertness and attention within the first 1 to 2 hours after consumption, with no reported side effects.

An additional research paper found that frequent tea drinkers had up to a 64% lower risk of having any brain function decline. This effect was particularly relevant for black oolong tea drinkers.

Because oolong tea is rich in EGCG polyphenols, it helps to maintain and improve hippocampus function and efficiency.

The hippocampus, part of the limbic system, is associated with motivation, emotion, learning, and the formation of new memories.

Regularly drinking black, green or oolong tea improves cognitive memory, function and information processing speed.

7. Improves Cardiovascular and Heart Health

Heart disease is the number one killer of men and women in the United States, sitting at 24% of total deaths.

Water and tea are the most consumed drinks on the planet, and for good reason. Proper hydration has a direct impact on blood pressure, which increases as you become less hydrated.

Drinking enough water every day (10 to 12 cups) is a great way to raise your energy levels and reduce your risk of heart diseases.

Having oolong tea daily amplifies these benefits because of all of its antioxidants. These antioxidants are the root source of the heart health benefits of oolong tea.

Additionally, they help to reduce bad cholesterol levels and total blood pressure.

Many recent studies show that people who were drinking 6 cups of tea a day reduced their risk of heart disease by over 50%.

More specifically, a study conducted with over 76,000 Japanese adults determined that having just 1 cup (8 oz) of oolong tea per day had a 62% lower risk of heart disease.

Oolong indirectly helps to fight against heart disease and high blood pressure by diminishing hypertension, controlling blood pressure, and the prevention of strokes.

It’s usually recommended to have any herbal tea a few days after an intensive surgery. Although oolong tea has a good amount of caffeine, which can raise blood pressure in caffeine-sensitive people. This effect diminishes with regular caffeine intake.

loose leaf oolong leaves on a spoon

Oolong Tea Side Effects

1. Oolong Tea Extracts Can Cause Liver Damage

Regularly drinking oolong tea offers many health benefits for your liver.

Herbal and Chinese teas can have serious negative side effects if you consume too much. Polyphenols are pigments contained in the tea leaves that have either a brown, yellow, or green color.

Multiple studies involving mice were tested with overconsuming of tea polyphenols, flavonoids, and flavanols. The study found that these plant-based compounds contributed to heightened liver toxicity in all mice.

People taking tea supplements or extracts have a greater chance of causing liver toxicity and other liver complications than individuals consuming regular brewed tea.

This is especially because of the higher concentrations of tea polyphenols in tea extracts. One tea per day is not going to produce the same effect.

2. Caffeine Overdose Causes Multiple Side Effects

Because oolong tea leaves are high in caffeine, drinking some frequently in large amounts can cause and produce headaches.

Caffeine is an addictive substance to most people, so consuming too much oolong tea could bring the risk of developing an addiction or dependency.

Some of the negative side effects of caffeine may also induce a risk of developing arrhythmia, heart palpitations and irregular heartbeats, insomnia, anxiety, and other heart complications.

Caffeine can also increase the severity of already existing digestive issues, especially for people who have diarrhea.

Additionally, for people suffering from glaucoma, the high amount of caffeine in oolong tea can increase the pressure within the eyes, possibly making this disease and it’s symptoms even worse.

white tea to black oolong tea

3. May Cause Issues During Pregnancy

Oolong tea has an ingredient called epigallocatechin (EGCG), which is a powerful antioxidant.

Just by themselves, antioxidants can help to prevent cell destruction, DNA degeneration, and the cell degradation that comes with ageing.

During pregnancy, EGCG can block the absorption of folic acid, which is also known as folacin or vitamin B. Folic acid is used for the reproduction of DNA, RNA, and to metabolize amino acids. Vitamin B is a crucial nutrient during pregnancy.

Medical professionals state that folic acid is one of the most important nutrients for developing children in expecting mothers.

Since EGCG can block the absorption of vitamin b, you should restrict how much herbal or oolong tea you drink per day during pregnancy. To keep a margin of safety you should not exceed 2 cups on a given day.

4. Can Negatively Interact With Multiple Drugs

Not enough conclusive studies have been done on the side effects of some pharmaceutical drugs with the consumption of oolong tea.

The significant leading cause of pharmaceutical drug side effects and complications comes from the consumption of too much caffeine.

Allopathic types of antibiotics interfere with the breakdown of the caffeine chemical in your body.

In some cases, doctors and health care professionals will tell their patients to cut down or even completely cut out caffeine while on these antibiotics, especially general use antibiotics such as Cipro.

Most Chinese teas contain a good amount of vitamin K. Vitamin K reduces the effectiveness of drugs and medicine that helps thin your blood, prevents blood clotting, and keeps your blood pressures lower.

Many patients on blood thinners should speak with a health care professional and provider before consuming more than 3 cups of oolong tea a day.

green oolong tea on a marble table

Rating and Recommendation

Extremely Recommended

Oolong tea leaves have micronutrients, plant-based metabolites, polyphenols, flavanols, flavonoids, catechins, and other ingredients that do not work well with some modern medication and other drugs.

Here’s the list of nutrition facts and health benefits of oolong tea:

  1. Improves Overall Lung Health and Can Alleviate Symptoms of Asthma

  2. Helps Control Blood Sugar Levels and Hypoglycemia

  3. Increases Metabolism And Helps With Weight Loss

  4. Improves Bone Mineral Density and Tooth Strength

  5. Reduces The Risk of Heart Disease

  6. Treats Skin Infections, Conditions, and Eczema

  7. Oolong Tea Boosts Cognitive Brain Function

  8. Improves Cardiovascular and Heart Health

  9. Reduces Cholesterol Levels

Here’s the list of side effects of oolong tea:

  1. Tea polyphenols can cause a risk of developing and causing liver damage

  2. Too much caffeine can increase the risk of developing arrhythmia

  3. May cause issues during pregnancy

  4. Can negatively interact with multiple drugs

Traditional teas have had extensive scientific studies performed on them to ensure quality, safety, health benefits, and side effects of non-herbal teas. Some non-herbal teas include earl grey tea, green tea, chamomile tea, white tea, and oolong tea.

Here are some conflicting oolong tea compounds with medication:

  • Caffeine does not work well with modern general case antibiotics. Antibiotics decrease the half-life break down of caffeine in your body, increasing your risk of any side effects.

    Some include increased heart rate, headaches, jitteriness, anxiety, muscle breakdown, as well as other effects. Birth control pills behave similarly to antibiotics in regards to caffeine.

  • If you’re taking blood thinners should be careful with the quantity of herbal and non-herbal teas you’re drinking.

    Since oxidized herbal teas contain antioxidants like vitamin K, it makes blood-thinning medication less effective, and in some cases completely ineffective.

    Some of the healthy plant-based compounds in oolong tea can slow blood clotting, amplifying the existing lingering effect of blood thinners. Avoid all acetylsalicylic acid-based medications, like aspirin.

  • Multiple health care and alternative health care providers state the importance of certain herbal teas with optimal pregnancy health.

    Pregnant or expecting mothers should be careful of their caffeine intake since caffeine crosses the placenta barrier and reaches your developing child.

    Developing babies can’t metabolize caffeine the way an adult would. Keep your caffeine intake to a minimum, it’s best to try to eliminate it entirely while pregnant.

Frequently Asked Questions

Oolong tea originates from China, made by simply using hot water with loose oolong tea leaves.

Oolong tea is a traditional drink that's been consumed for centuries and its manufacturing process remains closely the same.

All oolong tea leaves are made using the Camellia Sinensis plant, similar to black tea, green tea, and white tea.

The oolong tea leaves are extracted from the Camellia sinensis plant and dried to strengthen the flavor. Which increases the level of oxidation, deepening the flavor and darkening the color.

The longer the tea leaves oxidize for, the darker the color of the tea and it's leaves. White tea is the least oxidized and black tea is completely oxidized.

You can make green tea, yellow tea, white tea, and black tea out of the Camellia Sinensis plant.

White tea is the safest tea to drink since it has almost no caffeine, which is the main side effect of every type of non-herbal tea.

All herbal and non-herbal teas are safe to drink in moderation, there are certain restrictions such as when you're pregnant and if you take certain prescription drugs.

The main difference between herbal and non-herbal teas, such as oolong tea, is their levels of oxidation and levels of caffeine.

Herbal teas have no caffeine while non-herbal teas vary from 10 mg to 110 mg per cup.

When oxidizing Camellia Sinensis leaves, it releases enzymes that stimulate and expedite the drying process.

Turning the light green leaf into deep black color over time, which closely resembles earl grey tea. Earl Grey tea is made with black tea leaves and bergamot essential oil.

The green tea does not fully oxidize until it turns black. In the case of oolong tea, it's partially oxidized keeping some of it's lighter green color.

The partial oxidation makes the color of the tea leaves a shade of light brown with a unique taste that's different from most green and black teas.

The color of oolong teas varies from one brand to another, ranging from light green to dark brown.

Oolong tea tastes similar to earl grey tea minus the addition of bergamot essential oil.

A rich, dark, earthy flavor with a hint of grassy-ness. Some manufacturers infuse floral and other healthy ingredients such as:

1. Chamomile or other flowers including lavender and roses

2. Ginger

3. Mint leaves

4. Ginseng

5. Caramel

6. Milk

7. Coconut oil

8. Liquor

Oolong tea is oxidized to various degrees, this process creates different versions of teas and flavors as the leaves dry.

The flavor can be range from a light subtle taste to a bold, strong, dark tasting tea depending on the brand.

The light taste would be a form of white tea while the stronger taste would be a form of black tea. The range of oxidation also affects and reflects in the color of the tea and its leaves.

Oolong tea is caffeinated non-herbal tea that has a high amount of caffeine. Ranging from 10 mg to 95 mg of caffeine per cup depending on the range of oxidation and methods of processing.

The more oxidized the tea leaves, the more enzymes that will be released which produce caffeine.

White tea has almost no oxidation while green tea has a moderate amount, both having between 5 mg to 75 mg of caffeine per 8 oz cup.

While black tea, which is heavily oxidized has around 50 mg of caffeine per 8 oz cup.

Oolong tea has a lot of plant-based compounds including polyphenols, catechins, and flavanols, which are the main sources for its health benefits.

One of the health benefits of oolong tea is that it causes weight loss by increasing your metabolic rate by up to 13.4%.

These polyphenols reduce internal inflammation and increase your body's energy expenditure, in addition to its weight loss effects.

Oolong tea's plant-based compounds also help satiate and suppress hunger for up to 24 hours after ingestion, when paired with your meals it'll help you stay fuller for much longer.

Additionally, multiple studies found that flavanols, catechins, and polyphenols may also help clear out bad LDL cholesterol by up to 32%.

This improves blood pressure and increases your metabolism in the process, further promoting oolong's weight loss and health benefits.

Articles and Sources

cup of oolong tea

Oolong Tea Nutrition Facts

Serving Size 245 g (about 8oz or 1 Cup)

Amount Per Serving
Calories 2.4 Calories from Fat 0
% Daily Value*
Total Fat 0 g 0 %
Saturated Fat 0 g 0 %
Polyunsaturated fat 0 g
Monounsaturated fat 0 g
Trans Fat 0 g
Cholesterol 0 mg 0 %
Sodium 4 mg 1 %
Potassium 16 mg 1 %
Total Carbohydrate 0.3 g 0 %
Dietary Fiber 0 g 0 %
Sugars 0 g
Protein 0 g
Vitamin A 0 % Vitamin C 0 %
Vitamin E 0 % Vitamin K 0 %
Vitamin D 0 % Vitamin B6 0 %
Calcium 0 % Iron 0 %
Magnesium 0 % Cobalamin 0 %

Calories per gram:

Fat: 9 | Carbohydrate: 4 | Protein: 4

Source: USDA's Nutrient Database

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