No proof tea is the 'elixir of life'

"Is the elixir of life as simple as two cups of tea?," the Mail Online asks, prompted by a study looking at whether tea drinking is associated with a longer life expectancy in women.

This study included more than a thousand older women with an average age of 80. The women completed food and drink questionnaires, and the data from this was put into special databases to estimate their flavonoid intake.

Flavonoids are plant compounds found in various foods and drinks, including tea, chocolate and wine. They are said to have an antioxidant effect by helping prevent cell damage.

The researchers looked at how flavonoid intake was linked to the women's risk of death from any cause over the next five years.

They found those with the highest intake had a reduced risk of death compared with those with the lowest. In this group of older women, black tea contributed the most to total flavonoid intake.

However, although the study did find a link, this does not prove that tea or flavonoids are the single direct cause of reduced mortality. Various unmeasured health and lifestyle factors (confounders) could have influenced the results.

There are also possible inaccuracies in the estimation of flavonoid intake, and the results of this older group of Australian women cannot be applied to everyone.

Overall, this study does add to the body of research assessing flavonoids, but provides no proof that the compound – or tea specifically – reduces mortality in older women.

Where did the story come from?

The study was carried out by researchers from the University of Western Australia.

It was funded by Kidney Health Australia, Healthway Health Promotion Foundation of Western Australia, Sir Charles Gairdner Hospital Research Advisory Committee, and project grants from the National Health and Medical Research Council of Australia.

It was published in the peer-reviewed American Journal of Clinical Nutrition.

The Mail Online's coverage hailing tea the "elixir of life" has not taken into account the important limitations of this research.

What kind of research was this?

This prospective cohort study followed a group of older women over the course of five years to explore any links between flavonoid intake and overall mortality.

Flavonoids are plant compounds thought to have various potential health benefits, including effects on the cardiovascular system and glucose metabolism. Particularly rich sources include tea, chocolate, fruit and red wine.

Though previous research has investigated the link between flavonoids and particular health outcomes such as cardiovascular disease and cancer, there is said to have been little research investigating all-cause mortality.

Cohort studies such as this can demonstrate associations but cannot prove cause and effect, as other factors could be involved.

What did the research involve?

This study included 1,136 postmenopausal women (aged over 75) taking part in the Calcium Intake Fracture Outcome Age Related Extension Study that started in 2003. This was an extension of a randomised controlled trial of calcium supplements to prevent fractures.

The study included 1,063 women who completed food questionnaires in 2003. These questionnaires included questions on average tea and coffee consumption over the past 12 months.

The study then followed up all-cause mortality over the following five years to 2008, linking the women to database registries. These recorded cardiovascular and cancer events using valid medical codes, and deaths were also identified in the mortality register.

The researchers used two different databases on the flavonoid composition of different foods and drinks so they could estimate flavonoid intake.

They then looked at the link between all-cause mortality and flavonoid intake. They took into account potential confounders recorded at the start of the study.

These included existing cardiovascular disease and cancer recorded in the registries, age, body mass index (BMI), self-reported smoking status, alcohol consumption, fruit and vegetable intake, and physical activity.

What were the basic results?

Over the five years of follow-up, there were 129 deaths (12% of women). Average daily flavonoid intake was 674-696mg a day, depending on which of the two databases was used to estimate flavonoids.

Higher flavonoid intake was associated with a reduced risk of all-cause mortality. Compared with women with the lowest intake (less than 525 or 547mg a day), those with the highest intake (above 788 or 813mg a day) had a 62-64% significantly reduced risk of mortality – again, depending on which database was used to estimate flavonoids.

The researchers found similar results when looking specifically by cause of death, whether cardiovascular or cancer.

When the researchers looked specifically at flavonoids, black tea appeared to be the major dietary contributor. Tea accounted for between 59% and 82% of the total flavonoid intake.

How did the researchers interpret the results?

The researchers said that, "Using the most comprehensive flavonoid databases, we provide evidence that high consumption of flavonoids is associated with reduced risk of mortality in older women. The benefits of flavonoids may extend to the [disease cause] of cancer and cardiovascular disease."

Conclusion

Flavonoid plant compounds have been researched extensively, with studies exploring their possible health benefits.

In this research, there is an association between higher flavonoid intake and a reduced risk of death from any cause over five years in a cohort of older women.

However, this study provides no proof that drinking tea will help you live longer. There are several important points to bear in mind:

The design of this study cannot prove cause and effect. Though it has adjusted for various potential health and lifestyle confounders, it is unlikely to have taken all of them into account. It is therefore not possible to say that flavonoids are the single direct cause of reduced mortality.
This is a very specific population group: postmenopausal women with an average age of 80 who were recruited to a trial investigating calcium supplements to prevent fractures. They therefore may not be representative of all older women – for example, the women in this trial were of quite high socioeconomic status. Their results can certainly not be applied to women as a whole, or men.
Foods and drinks were assessed by food frequency questionnaire. Although these may be validated ways of assessing intake, they are still subject to inaccuracy. For example, people may not be able to give a reliable indication of their tea consumption over the past year.
This information on foods and drinks was put into two different databases to estimate flavonoid intake. As the results showed, the total intake amounts, or the risk reductions, varied depending on which of the two databases were used. This means these may not be completely accurate estimates of flavonoid intake.
The media linked these findings to tea, as black tea was the major source of flavonoids, though the main risk analyses were not solely based on flavonoid intake from tea. The researchers say an intake of about 350mg is equivalent to approximately two cups of tea, so the highest intakes of 788 or 813mg a day would be equivalent to more than four cups of tea.

Overall, this study adds to the body of research assessing the benefits of flavonoids, but provides no proof that they – or tea specifically – reduce mortality in older women.