Type 2 diabetes is less common in countries where people often enjoy high tea, a statistical model suggests.

The number of people with diabetes has increased nearly six-fold over the past few decades, stimulating interest in how foods could play a role in prevention, researchers said.

Black tea consumption was highest in Ireland and lowest in South Korea. (Cathal McNaughton/Reuters)

Calling tea the most widely used ancient hot beverage in the world, a team of French, British and Swiss researchers mined information on tea consumption in 50 countries based on 2009 sales data from a market research firm and looked for any correlation to five major diseases.

"We observed that, among the five health indicators, only the 'prevalence of diabetes' indicator appeared to have a strong statistical relationship with black tea consumption," Ariel Beresniak of Data Mining International in Geneva and co-authors concluded in Thursday's issue of the journal BMJ Open.

The correlation only points to a potential cause that needs to be further investigated, they cautioned, noting that establishing causality is one of the most difficult challenges in public health.

In the study, consumption of black tea was highest in Ireland at nearly 2.16 kilograms per year per person and lowest in South Korea at 0.0007 kilograms per year per person. Canada was at about the midpoint for consumption at less than 0.5 kilograms per year per person.

But the quality and consistency of consumption and health data among the 50 countries likely varied.

Other factors that weren't considered in the analysis may also be important, the researchers said.

The findings do back those of previous research, including a similar study in Europe.

While interest has grown in drinking green tea for its flavonoids in industrialized countries, black tea still represents 90 per cent of the tea sold in the West, the researchers said. In contrast, the Chinese population drinks 30 times more green tea per inhabitant than black tea.

Green tea is fermented to form black tea, keeping the caffeine about the same while different flavanoids are released. Flavanoids including theaflavins and thearubigins are thought to carry potential health benefits.

One of the authors is employed by Unilever and provided access to the global tea consumption data without any financial agreement or grant to support the study, which was carried out independently.