While it is safe to take vitamins before bed, most health care experts do not recommend it. According to the New Health Guide, taking vitamins can boost energy and work as a stimulant. This could make it difficult to fall or stay asleep.
The New York Times reported on a study done in 2007 that showed a possible association between taking multivitamins at night and poor sleep, but the results did not conclusively prove a link between the two. Many doctors also recommend taking vitamins with breakfast or lunch because the body is able to absorb them better when they are taken with food.