A once daily dose reduced PSA level an indicator of severity of disease by as much as half in 20% of patients.
There has been much interest in vitamin D in prostate cancer after studies linking risk of the disease to sunlight exposure, the researchers said.
One expert agreed the findings were encouraging but said it needed to be tested in a bigger population.
The trial results of which are due to be published in the journal BJU International was set up after one patient got better when his wife bought him some vitamin D tablets.
Professor Jonathan Waxman, said the example had prompted him to assess the effects in a wider group of patients.
April 28, 2009