Recent reports suggest that tea can cause brittle bones – but you'll probably be safe if you drink less than a gallon a day

• 
• • Luisa Dillner
  • The Guardian, Monday 1 April 2013
  •  ()

Tea … don't drink more than a gallon a day. Photograph: Getty Images

Do you fancy a cuppa? We drink, on average, three mugs a day. But you might want to try another tipple after hearing the case of a 47-year-old woman, published in the New England Journal of Medicine (NEJM), who developed brittle bones and lost all of her teeth after drinking too much tea.

Tea may not be so great for prostates either. Last year, research from the University of Glasgow found that men who drank more than seven or more cups of tea a day had a 50% higher risk of prostate cancer. And in 2009 a paper in the British Medical Journal showed that drinking very hot tea (70C or more) increased the likelihood of oesophageal cancer.

Still gasping for that cuppa? There is some evidence that tea can be good for you too, with antioxidant properties, so maybe you're not actually drinking enough of the stuff.

The solution

The poor woman in the NEJM study is not alone. There are a few other cases of people who have damaged their bones through too much tea. But she (like those in other studies) was drinking excessive amounts: 100-150 tea bags a day to make 12 cups of tea. A litre of tea can contain up to 9mg of fluoride, which in excess can cause skeletal fluorosis, reducing bone quality and causing pain and stiffening of the ligaments. Other studies show you generally need to drink a gallon a day for three decades to develop this condition.

You also shouldn't worry about the Glasgow study as it wasn't designed to show that drinking tea actually caused prostate cancer. All it proved was an association and people were only asked how much tea they drank at the start of the study, which went on for about 28 years.

The National Cancer Institute in the US concludes that the evidence isn't good enough to say tea either harms or helps our health. However it does seem sensible in the light of the BMJ study to wait for your tea to cool down for a few minutes.

Black tea, which makes up 75% of the world's consumption, may have healthy properties from its plant chemicals called polyphenols, which are antioxidants. Green tea contains more polyphenols but isn't so nice to dunk digestives into.

A review of the evidence in the European Journal of Clinical Nutrition, sponsored by the Tea Council – which, the authors say, had no part in the study – found the research showed more than three cups of black tea a day reduced heart disease. It found no evidence of harm "in amounts typically consumed". So as long as you drink less than a gallon of tea a day you should be absolutely fine.