Ayurveda believes you should get your daily nutrients out of food as much as possible, and you can do this by eating plenty of fresh vegetables, fruits, grains, beans and legumes, nuts and seeds, healthy meats and seaweeds. That said, there are cases in which it makes sense to supplement your diet with vitamins. Vegetarians should take vitamin B12 and possibly vitamin D, since they are missing out on these nutrients by not eating meat. Pregnant women should take extra folic acid. Those with osteoporosis will need to take extra calcium, magnesium, trace minerals like boron, and other supplements that specifically support their bone health. People recovering from a long illness may need to take certain immune-boostig supplements.
Its important to keep in mind that the American soil from which most of our food derives from is significantly depleted of nutrients, and as a result, our food is not as nutritious as it once was, which begs the question of what if we are even getting enough nutrients by eating a wide variety of foods. If this is of concern to you, you may consider taking a general mineral supplement or daily multivitamin. Whenever possible, ingest supplements that are extracted from a whole foods source like fruits, vegetables and grains. These will have the best bioavailability, meaning the highest absorption rate by your digestive system. The best way to take vitamins and minerals in is powdered from, liquid concentrate or as a oil. Avoid taking mega- doses or and dose larger than recommended dietary reference intakes, no matter how good you think they may be for your health.
Supplementing your diet with vitamins should be the exception, not the rule, they are, after all, called supplements. Nutrients are much more accessible and easily processed by your body when they are consumed in food forms versus supplement form. Also, there is the danger that a person taking vitamins will then rationalize that there is no need to focus on balanced nutrition from food, but there is no magic bullet and no replacement for a diet of healthy, whole foods.