Three glasses of red wine a week can help lower blood pressure, a study has found.

A higher intake of foods rich in flavonoids - including berries, apples, tea and red wine has been linked to lower blood pressure in analysis by Queen's University in Belfast and Kiel University in Germany.

Moderation is key, with researchers finding that about three glasses of red wine per week was optimal, while for berries the suggested amount was 80g a day.

The study focused on how microbes in the gut break down flavonoids found in those foods and drinks, which then results in a drop in blood pressure.

"Our gut microbiome plays a key role in metabolising flavonoids to enhance their cardioprotective effects, and this study provides evidence to suggest these blood-pressure-lowering effects are achievable with simple changes to the daily diet," said lead investigator Professor Aedin Cassidy.

The analysis involved more than 900 participants in Germany.

Previous research has shown flavonoids can improve heart health, but researchers said this was the first time their connection to lower blood pressure has been explained.

The study's results have been published in Hypertension, an American Heart Association journal.