So what is the truth?
Should you take supplements or not, and if so, which ones?
As with so many things when it comes to health, the real answer is...it depends.
Secondly, if you are not deficient in something, then taking a vitamin to correct a deficiency will obviously do nothing for your health. Most studies of multivitamins don't show any effect therefore, because they aren't targeting people that are specifically deficient in something (as a 2012 report by Dr. Moser in the International Journal of Vitamin Research explained, if the studies focused "just on people whose nutritional levels were known to be deficient, they would show a benefit from supplements"). Most grocery store multivitamins also contain the bare minimum (or less) of each vitamin - certainly not a therapeutic dose of anything.
Also, although chronic vitamin deficiencies have been linked to all sorts of diseases, they are not the only risk factor. Many other things come into play as well, such as stress, toxicity, hormone levels, exercise and fitness, diet, and many other issues. Whether or not you are deficient in a certain vitamin, if you take a multivitamin and make no other changes to your lifestyle, vitamins by themselves are unlikely to have much of an effect - unless you are severely deficient in a specific vitamin to the extent where that alone is causing an illness - in which case, therapeutic doses of that specific vitamin would show an obvious effect.
So what is the answer? Should you take vitamins or not? In short, perhaps, but with several caveats.
1. Understand that if you're not deficient in it, you won't benefit from taking a certain vitamin, so a multivitamin may not be all that useful for you.
2. Eat a healthy, balanced, nutritious diet, and after following this for several months, have your doctor check your blood levels of various vitamins and minerals - then take only those in which you are deficient.
3. Lead a healthy lifestyle - don't smoke or drink alcohol or caffeine in excess, avoid sugar, get regular exercise, and follow stress relieving practices.
Understanding and following these practices will help keep you healthy much longer and more effectively than just popping a pill every day. And if you are deficient in several different things, and wish to take a multivitamin, you will need to find a good quality one that has high enough concentrations of the vitamins to actually make a difference in your health. In most cases, these doses will need to be much higher than the RDA. For example, if you are deficient in Vitamin D (which many people in North America are), the paltry 400 IU RDA will do nothing for you - you may need upwards of 5,000 IU per day for an extended period of time to correct the imbalance. Your doctor can run a blood test and tell you if you are deficient. In some cases, he may even recommend a prescription-strength supplement, as Vitamin D is one of the most important for a healthy immune system, and deficiency has been linked to many types of cancers, osteoporosis, and more.
But how do you find a good quality supplement? There are many out there, and I don't claim to know what is best. However, I would suggest looking for those that contain whole foods, which are more balanced and easier for your body to absorb than any synthetic versions. Personally, I like Garden of Life - they do contain whole foods, raw foods, organic ingredients, are made in the US, and the company uses sustainable energy practices - which I like. I've also heard very good things about Standard Process, although they are more expensive. There are other good ones out there as well - look for naturally sourced and whole-food derived vitamins instead of synthetic, and in doses high enough to correct whatever deficiencies you have.
And remember, like anything else when it comes to health, there is no "magic pill," and the vitamins you need to maintain good health may be completely different from the ones your brother, sister, neighbor, or co-worker needs. Find out what you need, and take that.
Hopefully that clears up some of the confusion about supplements for you!