Most nutritionists agree that it is usually not necessary to take supplements if you are a healthy person. If you maintain a well-balanced diet, you are probably meeting most of your needs. However, taking a multi-vitamin is not a bad idea just for the purpose of a giving you a simple "insurance policy".
First, determine if you need to take a multi-vitamin. Use an online software program that allows you to analyze what you eat, in terms of daily nutrient intakes. You can use MyPyramid.gov and select My Pyramid Tracker. Record everything you eat for three to five days and take a look at each day to determine if you are falling short on some of your vitamins, minerals and/or nutrients. Common shortages include Vitamin E, Vitamin D, Calcium, and Fiber (among others).
If you notice some deficiencies, don't just jump into taking vitamins. First look to see how you can increase your vitamin intake through food. Getting your nutrients from food is the ideal way to get them because it is how the nutrients are chemically combined in the foods that gives them optimal bioavalability (meaning the efficiency of absorption). Another factor to consider, is that there are many benefits we get from foods that we can not get from a multi-vitamin, such as energy (which vitamins do not provide), natural fiber, protein and natural fats. There are also factors that have not yet been clarified by science, but we do know that certain nutrients, such as fish oils, are more effective when they come from fish rather than fish supplements. It is believed this is because there may be other factors involved in the chemistry of the fish itself and how essential fats are chemically bound to these other factors.
But if you decide that you prefer to take a multi-vitamin as an insurance policy, don't be fooled into thinking that you need to mega-dose or spend a lot of money. First, look at the % Daily Value. Try to stay at around 100% or less for each nutrient (a little bit over is fine, however, you don't need 500% of anything). Secondly, buy the most basic and cheap vitamin you can find. There is nothing superior in the $40 bottle vs. the $8 bottle. Third, look for artificial ingredients, colors, preservatives. If they are in the bottle, pass. Finally, go for a non-iron version. Men do not need near the amount of iron that women (pre-menopause) need and should not supplement with iron unless prescribed by a doctor. Some argue that women should take a multi-vitamin with iron because of menstruation, but I personally do not think this is necessary unless you show signs of anemia. Iron is one mineral that you can overdose on and you need to be careful with intake. Iron supplementation should really only be done when prescribed by a doctor. It is easy to get your daily dose of iron from foods such as chicken (especially dark meat), turkey, beef, halibut, crab, pork shrimp, spinach, beans, oatmeal, and fortified breads.
And if you find you are low in some of the common deficiency areas, here are some good sources of Vitamins E, D, and Calcium.
Vitamin E: Vegetable oils, Wheat Germ, Sunflower, Hazelnuts, Peanuts, Broccoli and Spinach.
Vitamin D: Salmon, Mackerel, Tuna, Milk, Margarine, Cereal, Egg, Cheese
Calcium: Milk, Yogurt, Cheese, Tofu, Leafy Greens, Cottage Cheese, Bony Fish, Salmon, Calcium-Fortified Cereals and Orange Juice