If you need to take a multivitamin, you'll want to take it in a way that maximizes absorption of its nutrients (i.e., essential vitamins and minerals) but is convenient enough so that you don't skip taking it. For many people, breakfast is the most convenient time to take a multivitamin, but if your breakfast does not include significant amounts of fats or oils, you won't get the best absorption of vitamin D and other fat soluble vitamins -- A, E, and K. In that case, take your multivitamin with whichever meal contains the most fats and oils. Taking your multivitamin with a meal may also reduce stomach upset or nausea that can occur with these supplements.
If you take separate supplements providing large amounts of vitamins or minerals, be aware that these can compete with the generally smaller amounts of similar nutrients in your multivitamin. For example, if you take a separate calcium supplement, take it at a different time of day than your multivitamin because the large amount of calcium will reduce absorption of minerals in your multivitamin, such as magnesium, iron, copper and zinc. Similarly, if you take a separate supplement with vitamin D, A, E, or K, take it at a different time of day than your multivitamin because it may reduce absorption of other fat-soluble vitamins in your multivitamin.
If you take a separate supplement with vitamin B12 (which 10 to 30% of older adults don't absorb well from foods), take it at least 6 hours apart from your multivitamin, because you can only absorb a small amount (about 1.5 mcg of B12) at a time. Taking small amounts of B12 twice daily is a good strategy to boost B-12 levels if needed and may be better than taking a large dose once a day.
Be aware that the calcium and/or magnesium in multivitamins may interfere with the absorption of certain medications, such as antibiotics, statins, and thyroid hormones. So, take them at a different time of day than your multivitamin.
When choosing a multivitamin, it's generally best to go with one that provides up to the daily requirement of each nutrient. Many multivitamins provide much more than you need, and this can potentially have negative effects. Check our Top Picks in our Multivitamin Supplements Review.