While a balanced diet provides adequate nutrition for most healthy people, dietary supplements may be helpful for individuals who restrict calories for weight loss or follow a vegan diet. Others that may benefit include older adults and those with conditions that inhibit nutrient absorption. The vitamins you need for healthy function include vitamins A, C, E, D, K and the B vitamins. Multivitamins often include most or all of the 13 vitamins essential to optimum health. However, in certain circumstances, some vitamins may impact the effectiveness of others when taken together.
In terms of meeting basic nutritional needs, taking a multivitamin that includes niacin, or vitamin B-3, is safe in combination with other nutrients. However, if you take niacin supplements to help control your cholesterol, certain combinations should be avoided. Vitamin A as beta-carotene, and vitamins C and E may reduce niacin's ability to improve good cholesterol levels, according to MedlinePlus.
One of the B vitamins, folate may be included in B complex vitamins and in multivitamins containing vitamin B-12. While taking folate and vitamin B-12 at the same time is not problematic in general, folate can mask a B-12 deficiency. Older adults, strict vegetarians and people with gastrointestinal disorders are at increased risk of vitamin B-12 deficiency. Low levels of vitamin B-12 can lead to anemia, a condition that folate may help correct. However, if the underlying B-12 deficiency is not addressed and corrected, permanent nerve damage can still result. If you are at risk of B-12 deficiency, seek your doctor's advice regarding proper supplementation.
Vitamin K plays a central role in your body's ability to properly form blood clots. If your doctor recommends a vitamin K supplement, avoid taking high dosages of vitamin E or vitamin A, which may counteract the effects of vitamin K. Additionally, if your blood clots too easily or quickly, your doctor may recommend avoiding vitamin K supplements and keeping food sources of vitamin K at a consistent level. Follow your doctor's advice about supplementation if you take blood thinning medication.
Dietary supplements vary in the nutrients they provide, as well as in the dosage of included nutrients. If you opt to take multivitamins, MayoClinic.com recommends choosing one that provides no more than 100 percent of the daily value of each nutrient. If your doctor prescribes a dosage higher than the daily value of a particular nutrient, disclose any other vitamin and herbal supplements that you take so that problematic combinations can be avoided.