Green tea is one of the most popular beverages consumed worldwide. It is made from the leaves of the Camellia sinensis plant and contains antioxidants and other beneficial plant compounds. Many health benefits have been associated with drinking green tea, such as weight loss, improved brain function, and a lower risk of heart disease and certain cancers. However, there has been some concern that green tea may increase blood pressure in certain individuals. In this article, we will examine the scientific evidence surrounding green tea and blood pressure.
Green tea ingredients that may affect blood pressure
Green tea contains several active ingredients that can have effects on the body. The main components in green tea that may impact blood pressure are caffeine and catechins:
Caffeine
Caffeine is a stimulant found naturally in the tea plant. It is the main active ingredient in green tea and accounts for approximately 25-30 mg per 8 oz cup. Caffeine’s main effect is to stimulate the central nervous system, which can lead to increased alertness and energy.
Caffeine also causes a short-term increase in blood pressure in some people. The exact mechanism is not fully understood, but it seems caffeine can block a hormone that helps keep arteries widened (1). This causes the arteries to constrict temporarily. Studies show that caffeine intake can raise blood pressure by 5-15 mm/Hg for up to 3 hours in people with hypertension and those who rarely consume caffeine (2). Tolerance to the blood pressure-raising effect builds up in people who regularly drink caffeinated beverages.
Catechins
Green tea contains several catechin antioxidants, with the most abundant being epigallocatechin gallate (EGCG). Catechins make up approximately 30% of the dry weight of green tea leaves. They provide many of its proposed health benefits.
However, catechins may also modestly reduce blood pressure. Animal studies have found catechins relax blood vessels, which allows for increased blood flow (3). The results of human trials have been mixed. Some show small decreases in blood pressure with green tea extract, while others show no effect (4, 5). It’s unclear exactly how catechins may improve blood vessel function. They seem to have anti-inflammatory and antioxidant effects that may help regulate factors involved with controlling blood pressure.
So in summary, the caffeine in green tea may raise blood pressure temporarily in some people, while its catechins may have a modest blood pressure-lowering effect. The combined result of these opposing influences likely determines green tea’s overall effect on blood pressure.
Does green tea consumption raise blood pressure in the short term?
Several studies have looked at the immediate impact that drinking a cup of green tea can have on blood pressure. The results suggest that green tea temporarily increases blood pressure in people who rarely consume caffeine but has little effect for regular tea drinkers:
– In a controlled study, 60 people with mildly elevated blood pressure drank either water or 2 cups of green tea after abstaining from caffeine for 2 days. Drinking green tea increased their blood pressure by 2 mm/Hg compared to water. The effect was greater in people with higher baseline blood pressure (6).
– A similar study in 93 people found that caffeine intake from either coffee or green tea caused a small increase in blood pressure. However, the effect was only statistically significant in those who consumed less than 200 mg caffeine per day, the equivalent of 2–3 cups of green tea (7).
– One study had participants consume 4 cups of green tea per day, containing a total of 558 mg caffeine. This high intake did not significantly increase 24-hour average blood pressure compared to placebo (8).
– A large analysis of 18 randomized controlled trials found that green tea beverages increased systolic blood pressure by 1.7 mmHg and diastolic blood pressure by 0.9 mmHg compared to placebo in people who did not regularly consume caffeine (9).
Overall, these findings indicate that green tea consumption may induce a modest, temporary rise in blood pressure of up to 5 mmHg in people with low regular caffeine intakes. Those who regularly drink tea or caffeine do not appear to experience such an effect.
Does long-term intake of green tea affect blood pressure?
While the immediate impact of drinking a cup of green tea may raise blood pressure for a few hours, it’s not clear if habitual long-term green tea consumption has any lasting effect on blood pressure regulation.
The evidence from randomized controlled trials is inconsistent:
– One study investigated the effects of drinking 5 cups of green tea daily in 60 overweight individuals. After 8 weeks, systolic and diastolic blood pressure had significantly decreased by roughly 5 mmHg compared to baseline (10).
– However, two larger studies found no difference in blood pressure between groups consuming green tea, green tea extract, or placebo capsules for 12 weeks (4, 11).
– Likewise, there was no significant difference in blood pressure between the green tea and control groups in a comprehensive analysis of 11 randomized controlled trials involving 821 participants (9).
The mixed results of these studies make it difficult to conclude whether green tea intake affects long-term blood pressure. Larger, higher-quality studies are needed.
There is more consistent evidence from observational studies that green tea consumption is associated with lower blood pressure over time:
– A study in over 1,100 Japanese adults found that drinking 5 or more cups of green tea per day was linked with approximately 2 mm/Hg lower systolic and diastolic blood pressure readings compared to drinking less than 1 cup per day (12).
– In a study of Chinese adults, regular green tea intake was associated with a 46% lower risk of developing high blood pressure over a 5-year period (13).
– A cross-sectional study in Japan reported that daily green tea drinkers had 3.1 mmHg lower systolic and 2.4 mmHg lower diastolic blood pressure than those who rarely drank green tea (14).
While these observational findings can’t prove causation, they suggest habitual green tea intake may help prevent an increase in blood pressure over time. Likely mechanisms could involve improved endothelial function and antioxidant protection. However, not all observational studies have found a benefit (15).
Summary
In summary, green tea may temporarily increase blood pressure by a small amount, but regular drinkers develop a tolerance. Longer-term data are mixed. Larger controlled trials are needed to provide clear conclusions. However, green tea has been linked to lower blood pressure and a reduced risk of hypertension in multiple observational studies.
Does decaffeinated green tea also affect blood pressure?
Because caffeine is one of the main components hypothesized to raise blood pressure, removing it may alter green tea’s effects.
Limited research suggests decaffeinated green tea does not appear to increase blood pressure:
– A lab study found that a decaffeinated green tea extract induced relaxation of blood vessel tissue. In contrast, caffeinated green tea had a more variable effect (16).
– In a small controlled trial, decaffeinated green tea did not alter blood pressure over 8 weeks compared to placebo (17).
– An analysis of five randomized controlled studies found that decaffeinated green tea beverages decreased systolic and diastolic blood pressure compared to placebo (9).
More studies are needed, but it appears removing caffeine from green tea eliminates any potential short-term blood pressure increasing effects. This implies the majority of green tea’s influence comes from its caffeine content.
However, decaffeinated varieties retain their content of catechins like EGCG that provide other proposed benefits. So decaf green tea may be optimal for those needing to avoid caffeine.
Who may be most sensitive to the effects?
Studies indicate that green tea is more likely to increase blood pressure in certain subgroups of people. Factors that may increase sensitivity include:
Being a non-regular caffeine consumer
Consuming caffeine only occasionally makes you more prone to its effects on blood pressure. Those who regularly drink green tea or other caffeinated beverages develop tolerance and see little to no impact on their blood pressure.
Having existing high blood pressure (hypertension)
People with hypertension seem more responsive to the blood pressure-raising effects of caffeine intake (6).
Older age
Blood pressure naturally tends to increase with age as arteries stiffen. Since the elderly often have higher baseline blood pressure, they may experience greater effects from compounds that influence blood pressure (18).
Taking certain medications
Caffeine can potentially interact with some medications that influence blood pressure regulation or narrow blood vessels, enhancing caffeine’s effects. Examples include medications for heart disease, anxiety, depression, and headaches (19).
Those who regularly monitor their blood pressure and need to keep it within a strict range should consult their healthcare provider before adding green tea to their daily regimen.
Tips for minimizing green tea’s impact on blood pressure
For most people, drinking green tea does not significantly affect blood pressure. However, for those concerned about a potential modest increase from the caffeine content, certain tips can help keep levels in check:
– Limit intake to 2-3 cups per day. Consuming excessive amounts may increase odds of unwanted effects.
– Choose decaffeinated varieties to remove the main component that raises blood pressure. Decaf still provides beneficial catechins.
– Avoid adding extra caffeine from sources like coffee, soda, and energy drinks.
– Gradually increase green tea consumption to allow time for your body to develop tolerance.
– Monitor your blood pressure when starting to drink green tea. This allows you to assess your individual response.
– Be cautious if combining green tea with medications that affect blood pressure or caffeine’s clearance from the body.
– Avoid drinking green tea within 1-2 hours of bedtime, as late day caffeine intake can disrupt sleep.
Green tea and blood pressure medication
Green tea does contain caffeine, so there is a potential for interaction with certain blood pressure lowering medications.
Particularly, caffeine has the strongest effect of reducing the concentration and effects of calcium channel blockers such as verapamil, diltiazem, and amlodipine. Calcium channel blockers relax blood vessels and are commonly prescribed to treat high blood pressure (20).
Caffeine may also interact with beta-blockers like propranolol and metoprolol. Beta-blockers reduce blood pressure by blocking the effects of the stress hormone adrenaline. However, this interaction is likely weaker and less clinically significant (21).
On the other hand, green tea is rich in antioxidant plant compounds, including catechins and quercetin. These may provide synergistic blood pressure lowering benefits when combined with traditional antihypertensive medications. For example, the ace inhibitor enalapril lowers blood pressure more effectively when combined with quercetin (22).
Overall, those taking antihypertensive medications, especially calcium channel blockers, should exercise caution when adding green tea to their regimen and monitor their blood pressure closely. Discussing any potential interactions with your healthcare provider is advised, as effects can vary between individuals. But for most people, moderate green tea consumption should not significantly interfere with common blood pressure treatments.
The bottom line
In summary, green tea contains caffeine that can lead to short-term increases in blood pressure of 2–5 mmHg. This effect is most pronounced in infrequent caffeine consumers and people with pre-existing hypertension. For others, green tea only has a negligible impact on blood pressure.
Longer term data on green tea’s relationship with blood pressure are inconsistent overall. However, they suggest habitual green tea intake may provide modest reductions in blood pressure over time and help prevent progression to hypertension.
If you have high blood pressure or take antihypertensive medications, limit green tea intake to 2–3 cups per day, choose decaffeinated varieties, and monitor your blood pressure after starting consumption. Doing so will allow you to assess your personal tolerance and minimize potential negative effects on blood pressure.
