According to Dr. David Williams, a multivitamin should generally be taken just before a meal. The Vermont Department of Health also recommends mealtime for vitamins, as the food will buffer the supplement and prevent stomach upset. Taking vitamins at mealtime also helps establish a regular schedule and prevents missed doses.
Dr. Andrew Weil explains that mealtimes are best for multivitamins due to the fact that several vitamins, such as A, D, E and K, are fat-soluble. This means they are absorbed more readily when consumed with food containing fat. Taking these supplements on an empty stomach could significantly reduce their effectiveness.