Exposing your skin to the Sun may help you live long as people with lower blood levels of vitamin D are twice as likely to die prematurely as compared to people with higher blood levels of vitamin D, research suggests."Three years ago, the Institute of Medicine (IOM) - the health arm of the National Academy of Sciences in the US - concluded that having a too-low blood level of vitamin D was hazardous," said Cedric Garland, a professor at University of California, San Diego.The new study supports that conclusion but goes one step further, Garland added.The 20 nanograms per milliliter (ng/ml) blood level cutoff assumed from the IOM report was based solely on the association of low vitamin D with risk of bone disease.This new finding is based on the association of low vitamin D with risk of premature death from all causes and not just bone diseases, Garland explained.The study included residents of 14 countries, including the United States, and data from 566,583 participants.The average age when the blood was drawn in this study was 55 years; the average length of follow-up was nine years.The blood level amount of vitamin D associated with about half of the death rate was 30 ng/ml, Garland added."This study should give the medical community and public substantial reassurance that vitamin D is safe when used in appropriate doses up to 4,000 International Units (IU) per day," Heather Hofflich, a professor in the UC San Diego School of Medicine, noted.The study appeared in American Journal of Public Health.