Does it work?

Can hibiscus tea help reduce blood pressure?

BACKGROUND

About a billion people around the world are estimated to have high blood pressure. It is one of the top 10 factors contributing to the global burden of disease. While effective pharmaceutical treatments are available, various lifestyle changes and dietary factors that may reduce blood pressure are being actively pursued.

One herbal remedy that has received much interest is hibiscus tea, also called sour tea or sorrel tea. Over 200 hibiscus species exist, well known for their beautiful flowers. The herbal tea is made from Hibiscus sabdariffa, also called roselle. The flowers are either white with a red centre or all red and are dried to give the material used to make teas. Many cultures use the flowers to make refreshing red drinks that can be served either hot or cold.

The teas have long been associated with many health benefits, including improved circulation. The hibiscus is now a symbol for the infamous Changi prison camp run by the Japanese when they occupied Singapore during the second World War. The plant was used as food and also thought to prevent sterility among the prisoners of war. Recent attention has focused on the use of hibiscus tea to reduce blood pressure.

EVIDENCE FROM STUDIES

Laboratory studies have shown that hibiscus extracts contain antioxidants and can reduce blood pressure and cholesterol levels. This has led to a number of studies in humans. A systematic review of this early research was published in January 2010. This found four randomised controlled trails of hibiscus tea for people with mild hypertension. Two studies found that hibiscus tea lowered blood pressure more than black tea, and two others found that while it was not as effective as ACE-inhibitors, commonly used anti-hypertension drugs, the tea still reduced blood pressure.

On average, people drinking hibiscus tea lowered their systolic blood pressure by about 15mmHg and their diastolic pressure by about 10mmHg. However, the reviewers concluded that these studies were of poor quality and that better designed, larger and longer studies were needed.

A high quality study was published in February 2010. This compared a hibiscus tea with a placebo drink designed to look and taste the same as the herbal tea using artificial colorants. The tests were conducted at the US Department of Agriculture, although funded by the tea manufacturer. Those participating had pre- or mild hypertension and were generally healthy. Those drinking hibiscus tea three times daily had significantly lower systolic blood pressure (by 6mmHg) compared with those drinking the placebo. The diastolic blood pressure dropped slightly, and by the same amount, in both groups. Another high-quality study with diabetic patients who had mild hypertension found significant reductions in systolic but not diastolic blood pressure.

PROBLEMATIC ASPECTS

In the clinical trials conducted, no side effects were reported. Coupled with the long traditional use of hibiscus beverages, these teas are likely to be safe to use.

However, this has not been carefully studied, and research into the best amount to take, and for how long, has not been conducted.

RECOMMENDATIONS

Hibiscus tea has a long tradition of use for circulatory problems. Recent research has consistently shown beneficial results in reducing blood pressure, particularly systolic blood pressure. While the studies have not been ideal, more recent, high quality studies have also had positive results.

However, the studies have used a variety of products, and it is currently difficult to know which brands are of the highest quality and how much active ingredient each contains.

Nonetheless, a few cups of hibiscus tea per day may provide some benefit for those with mild hypertension. Given the potentially serious effects of high blood pressure, anyone with hypertension should be monitored carefully by appropriate healthcare professionals.

Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University