Middle-aged women who swallow multivitamin supplements are not doing their health any favours – and are just creating expensive urine, according to the world's largest study into the subject.

Researchers who examined the pill-popping habits of nearly 162,000 American women aged 50 to 79 found that although they swallowed dietary supplements by the bucketload, there was no sign that they reduced common cancers, heart disease or deaths.

People who eat a healthy diet get all the vitamins they need from their food. Any excess of vitamins (the water soluble C, B1, B2 and B6), whether in the food or in dietary supplements, is excreted. Fat soluble vitamins (A, D, E, K) are stored in the liver and an excess can result in side effects.

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"Based on our results, if you fall into the category of the women described here and you do in fact have an adequate diet, there really is no reason to take a multivitamin," said Dr Sylvia Wassertheil-Smoller, professor of epidemiology at Albert Einstein College, Yeshiva University.

Around half of Americans use vitamin supplements, spending $20bn (£13.4bn) a year on the pills which are believed to improve health and longevity. In Britain, a Food Standards Agency survey last year found 31 per cent of adults claimed to be taking the supplements, which typically cost £7 for a month's supply. The market in the UK is estimated to be worth over £330m a year.

The researchers recorded around 10,000 cases of cancer, 9,000 heart attacks and 10,000 deaths, and compared the incidence among the women who took supplements with those who did not. Marian Neuhouser of the Fred Hutchinson Cancer Research Centre in Seattle, who led the study published in Archives of Internal Medicine, said: "To our surprise we found that multivitamins did not lower the risk of the most common cancers and also had no impact on heart disease."