Washington, Jul 15 (IANS): Black tea, the world's most consumed beverage, contains higher concentrations of fluoride than previously thought.

Fluoride helps prevent dental cavities, but excessive consumption causes advanced skeletal fluorosis, characterised by joint and bone pain.

"The additional fluoride from drinking two to four cups of tea a day won't harm anyone, it's the very heavy tea drinkers who could get in trouble," said Gary Whitford, professor of oral biology at Medical College of Georgia.

When Whitford began analysing data from patients with advanced skeletal fluorosis, he discovered that the fluoride concentration in black tea had long been underestimated.

Whitford tested seven brands of store-bought black tea, steeping each for five minutes in de-ionized water, which contains no fluoride.

He found that the amount of fluoride in each sample was 1.4 to 3.3 times higher than he thought.

An average person ingests a very safe amount, 2 to 3 mg daily, through fluoridated drinking water, toothpaste and food, according to a college release.

It would take ingesting about 20 mg a day over 10 or more years before posing a significant risk to bone health.

Whitford presented his findings at the International Association of Dental Research Conference in Barcelona, Spain.