Hibiscus Tea: The Brewing Method the Blood Pressure Trial Actually Used

Category: Circulation

How to brew hibiscus tea the way the trial did: 1.25 g per 240 ml, a 6 minute steep, three servings daily, plus an honest read of the blood pressure evidence.

Traditional uses & benefits

• This is an educational record about what hibiscus research has measured and how the tea was prepared in those studies
• It is not a treatment for any condition, and blood pressure is a matter for your doctor

Ingredients

• Dried hibiscus calyces (Hibiscus sabdariffa) (1.25 g per serving (about half a level teaspoon))
• Freshly boiled water (240 mL per serving)

How to prepare

1. Measure 1.25 g of dried hibiscus calyces, about half a level teaspoon, into a cup. This is the quantity the trial used per serving. 2. Pour over 240 mL of just boiled water. 3. Cover and steep for 6 minutes, which is the trial's steep time. Longer is not better and was not what was studied. 4. Strain. The liquid should be deep ruby red and noticeably tart. 5. Drink within about 20 minutes of brewing. Anthocyanins degrade on standing, particularly in light and warmth, so tea left for hours is a weaker product than the one that was tested. 6. Repeat for a total of three servings across the day, which is the frequency the trials used. One cup a day is not the studied regimen. 7. Sweeten only if you must, and be aware that sugar works against the cardiovascular purpose. Most people adjust to the tartness within a week. 8. If you take any blood pressure medication, or any medication at all, speak to your doctor or pharmacist before adding three cups of this to your day.

Why it works

Hibiscus is rich in anthocyanins and organic acids, and several mechanisms have been proposed from laboratory work including ACE inhibition and a mild diuretic effect. None has been confirmed as the operative mechanism in people.

Time to effect

The trial measured its outcome at 6 weeks. Any blood pressure change is something your doctor should be measuring, not something you should be inferring at home.

Not right for

Not for anyone who is pregnant or breastfeeding. Not for anyone on blood pressure medication without speaking to their doctor first, because the effects may add together and cause dizziness or falls. Not for anyone with low blood pressure or significant liver disease. And absolutely not a reason to change or stop any prescribed medication.

What the evidence says

McKay et al. (2010), a randomised double blind placebo controlled trial in 65 pre and mildly hypertensive adults drinking 240 mL of brewed hibiscus tea three times daily for six weeks: systolic pressure fell 7.2 plus or minus 11.4 mm Hg against 1.3 plus or minus 10.0 mm Hg on placebo. The diastolic difference was not statistically significant. Pooled across 7 trials and 362 people the systolic figure was a more modest 4.71 mmHg.

Who it suits best

Best for an adult who has read about hibiscus and wants an accurate account of what the trials actually did, who is not pregnant, and who is either not on blood pressure medication or has already checked with their doctor. Anyone with raised blood pressure should be managing it with their clinician.

When to take it

preventive

Common mistakes

• Brewing it far stronger than the trial did. The study used about half a teaspoon per cup steeped for six minutes. A heaped spoonful stewed for half an hour is not a better version of the study, it is a different drink, and this is an ingredient where more is explicitly not better.
• Drinking one cup a day. The trials used three servings daily. One cup is not the studied regimen.
• Letting it sit for hours or making a big batch for the week. Anthocyanins degrade on standing, so drink it fresh.
• Buying a floral blend where hibiscus is a minor flavouring. Check the label says Hibiscus sabdariffa and that it is the main ingredient.
• Loading it with sugar, which works directly against the cardiovascular purpose.
• Treating it as a substitute for medication. The pooled effect across trials is 4.71 mmHg, which is modest and nothing like the effect of an antihypertensive.
• Assuming a big effect because the headline trial showed 7.2 mmHg. The standard deviation was 11.4, which means individual responses varied hugely and many people had no change.
• Drinking it through pregnancy. Hibiscus is a clear avoid there, not a caution.

How we read the research

A randomised double blind placebo controlled trial in 65 adults, which published its brewing method (1.25 g per 240 mL, 6 minutes, three times daily for six weeks), plus a meta analysis of 7 trials giving a more modest pooled figure.

Sources

• Hibiscus sabdariffa L. tea (tisane) lowers blood pressure in prehypertensive and mildly hypertensive adults (McKay 2010, J Nutr) (2010): Randomised, double blind, placebo controlled trial in 65 pre and mildly hypertensive adults. Systolic blood pressure fell 7.2 plus or minus 11.4 mm Hg on hibiscus vs 1.3 plus or minus 10.0 mm Hg on placebo at six weeks (P = 0.030). Note the wide standard deviations, indicating highly variable individual response. Source of the three servings of 240 mL daily protocol.
• Effect of sour tea (Hibiscus sabdariffa) on blood pressure: a systematic review and meta analysis (Phytotherapy Research) (2020): Meta analysis of 7 randomised controlled trials, 362 participants total. Pooled systolic reduction of 4.71 mmHg. A modest effect derived from a small total sample, and not comparable to antihypertensive medication. Cited here to keep the effect size honest rather than to amplify it.

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.