more fluoride. They calculated a person drinking a litre of economy tea per day would consume about 6 mg of fluoride, above the recommended average dietary intake level of 3–4 mg of fluoride per day, but below the maximum tolerable amount of 10 mg of fluoride per day. Brick tea, made from fallen leaves, old leaves and stems has the highest levels. One study indicated that green tea leaves have an average fluoride concentration of 52 mg/kg, and approximately 89% of the fluoride was released from the leaves into tea after brewing. Oxalates Tea contains oxalate, overconsumption of which can cause kidney stones, as well as binding with free calcium in the body. The bioavailability of oxalate from tea is low, thus a possible negative effect requires a large intake of tea. Massive black tea consumption has been linked to kidney failure due to its high oxalate content (acute oxalate nephropathy). Theanine and caffeine Tea also contains theanine and the stimulant caffeine at about 3% of its dry weight, translating to between 30 mg and 90 mg per depending on type, brand and brewing method. Tea also contains small amounts of theobromine and theophylline. Dry tea has more caffeine by weight than dry coffee; nevertheless, more dry coffee than dry tea is used in typical drink preparations, which results in a cup of brewed tea containing significantly less caffeine than a cup of coffee of the same size. The caffeine in tea is a mild diuretic. However, the British Dietetic Association has suggested that tea can be used to supplement normal water consumption, and that "the style of tea and coffee and the amounts we drink in the UK are unlikely to have a negative effect [on hydration]". By conditions Cognitive effects Drinking caffeinated tea may improve mental alertness. There is preliminary evidence that the caffeine from long-term tea (or coffee) consumption provides a small amount of protection against the progression of dementia or Alzheimer's disease during aging, although the results across numerous studies were inconsistent. Cancer In 2011, the US Food and Drug Administration (FDA) reported that there was very little evidence to support the claim that green tea consumption may reduce the risk of breast and prostate cancer. A 2010 report by the US National Cancer Institute stated that epidemiological studies and the few clinical trials of tea for the prevention of cancer were inconclusive. The institute "does