As stated above, most people don't need a multivitamin. Though at a certain age, it is usually recommended to take one for continuing good health. One multivitamin a day will not be enough to get to toxic levels and are very safe. There are two types of vitamins, water-soluble and fat-soluble vitamins. The fat-soluble vitamins are the ones you would be more worried about, as with those there is a possibility of overdosing and having it be toxic. Though with a simple multivitamin you will not reach that level.
The reason to take a multi is that the food we eat in modern times is often lacking nutrients. There are several reasons for this. For one thing, unless you're eating organically grown produce, you're taking in a lot of pesticides, which can affect nutrient absorption, and the soil, treated with petroleum based fertilizer, has had the minerals leached out of it. If the soil lacks minerals, so will your food. For another thing, food is old when we eat it. Thanks to refrigeration, food can be pretty old by the time we eat it, and many of the nutrients will have lost potency by then due to oxidation and age. Third, most of us take medications that interfere with the absorption of nutrients. Fourth, most of us haven't a clue how to eat a diet suited to who we are anymore because we don't know who we are anymore. Different people are suited to different diets. Fifth, we eat a lot of frankenfoods, such as beef and wheat, that were invented by humans, not nature, and don't go down that well. Sixth, we take in so many toxins with each breath and drink and bite now that we need more antioxidants than we would otherwise. Seventh, we've created such an artificial life filled with artificial stress that it leaches out nutrients. Eighth, we've been told to eat so many foods that aren't good for us, such as fast foods and milk, that we no longer get minerals in their proper ratios. I could go on, but that should be enough to show why virtually everyone now recommends a multivitamin and mineral supplement. As to toxic levels, depends on which one you take. What is more likely is you won't absorb enough of the supplement, especially if you take drug store brands like Centrum, because they use the cheapest least absorbable stuff around. That's why there's so much in a multi, they're not as well absorbed as good food. If you want to avoid the need to take one, eat all organic food, find a diet that actually suits who you are, and emphasize colored vegetables for both minerals and antioxidants. Juicing is also great to maximize nutrient levels. This will take study. If you don't want to do this, take a multi.
All of the above is good advice.
One of the problems with a modern lifestyle is that most of us don't get enough exposure to sunlight to produce normal limits of vitamin D. It is produced when the skin surface is exposed to sunlight and is an important vitamin for emotional health and immunity. In this case a vitamin D3 supplement is useful.
Lately I make a habit of getting no less that 45 minutes a day of sunlight exposure, at least fifteen minutes with my shirt off, and it has really improved my outlook.
Paxilid has said most of what I wanted to.
I believe everyone would benefit from a good multi. It's difficult to get the vitamins and minerals from your foods, Paxiled has explained why quite well. The scary thing is that nearly 70% of people in the U.S. have a serious deficiency in 1 or more vitamins or minerals, and deficiencies can cause detrimental effects to people.
Paxiled, I do believe you are a genius...
I have seen your responses to many posts and your answers are always well founded and good. You seriously blow me away.
To everyone else, I would listen to this person, as well as do your own research. It's good to get answers on your own as well.
I wholeheartedly agree with your assessment of Paxiled. I also see you as a highly gifted young person! Keep learning and sharing your knowledge!