Researchers at the University of California have found that vitamin D3 - available as a supplement - has a protective effect only at levels of 1000 IU (international units) a day. The UK government's recommended safe upper limit dose is just 400 IU/day whereas, in the US, it's set at 2000 IU/day.
The study was based on scientific reports published between 1966 and 2004 regarding cancer and vitamin D, and concluded that thousands of lives could be saved if people had sufficient bodily stores of vitamin D.
Scientists reckon that around one in 10 people in the West are deficient in this vitamin. It is most readily available from the sun itself, but there are concerns that overexposure can lead to skin cancer. This is why it is recommended that people get the vitamin from supplements and from foods such as egg yolk, fish oil and liver (Am J Publ Health, published online, 27 December 2005).
* Further evidence that high-dose vitamins can have a therapeutic effect comes from a new study into age-related macular degeneration (AMD), a disorder of the retina that can lead to near-blindness. In this case, researchers found that regular, high doses of antioxidants - vitamins C and E, beta-carotene and zinc - could "substantially" reduce the risk of developing the problem.
AMD affects around 11 per cent of those aged 80 years and over, and sufferers can lose the ability to read, recognise faces, drive and move freely.
The condition appears to be related to a lack of oxygen - and the retina is made up of oxygen, polyunsaturated fats and photosensitisers. Not surprisingly, earlier studies into antioxidants found that supplements resulted in a 25 per cent reduction in progression of the disease, even in its late stages. The supplements used, however, contained between three and 13 times the RDA.
The new study, carried out by the Erasmus Medical Centre in Rotterdam, confirms the earlier findings. In a study of 5836 people at risk of developing AMD, the researchers found that a combination of vitamins C and E, beta-carotene and zinc resulted in a 35 per cent reduction in AMD risk (JAMA, 2005; 294: 3101-7).