Four times current vitamin D doses needed for winter levels:

Maintaining adequate levels of vitamin D during winter months requires a daily dose of 20 micrograms, four times the current recommended dose, says a new study. The study, led by Susan Sullivan from the University of Maine, has important implications for ongoing consultations on vitamin D recommendations, with the current level of five micrograms (200 International Units) seen by many as insufficient.
Read article at nutraingredients.com