Should I take a multi-vitamin everyday?

Ah, vitamins and supplements.  They are a huge money-making industry. Your local supermarket, GNC store, or Vitamin Cottage literally has shelves upon shelves of them. Calciuim, vitamins D, E, A, K, C, B, iron, glucosamine chondroitin, omega-3 fish oil, multi-vitamins, etc. etc. Vitamins have been studied extensively for their ability to prevent or improve outcomes in cancer, diabetes, heart disease, and so on.  The largest well-controlled scientific studies have actually found very little benefit in taking multi-vitamins or individual vitamins in preventing cancer, heart disease, dementia, diabetes, and other chronic diseases. In fact, some studies have shown that taking vitamins during cancer chemotherapy or afterward can increase the chances of the cancer reoccurring or metastasizing!  Apparently, cancer needs vitamins to grow, too.  For a long time it was thought that taking vitamin D helped to prevent breast cancer, but new studies show that taking vitamin D does not measurably decrease the risk of breast cancer.  Comparing rates of cancer, heart disease, diabetes, arthritis, stroke, dementia, etc. in large numbers of people who take vitamins to people who don't take vitamins shows almost no long-term benefits in vitamin-takers.  Conclusion: stop wasting your money buying vitamins and popping pills.  The exceptions: calcium/vitamin D supplements do prevent bone loss in women, and daily small doses of aspirin or ibuprofen help prevent heart attacks, stroke, and even lowers the risk of cancer.  
So what to do?  What has been found to help is eating a variety of fruits, vegetables, whole grains, lean meats, limiting processed meats, exercising regularly, sleeping enough each night, reducing stress, staying social and active even after retirement, and maintaining a healthy weight lowers your risk for developing cancer, diabetes, heart disease, arthritis, Alzheimer's disease, dementia, and on and on.  Sound daunting?  Work on one of the above first, and then start on the next one once you have that down pat.  Why do fruits, vegetables, grains, etc. help prevent disease and vitamins don't?  Well, for one thing our bodies absorb nutrients better from food rather than a pill.   A lot of the vitamins in a pill just go right through the other end. Also, it is possible that the combinations of different vitamins, fiber, water, antioxidants, and carbohydrates in fruits and vegetables work together in ways we just don't understand yet (it's called synergistic effects).  We cannot duplicate a healthy diet in convenient pill form! Plus, vitamins don't fill you up with healthy calories.  Eating a bunch of junk food and popping a vitamin just doesn't cut it.  So be wary when you read about the next vitamin or supplement craze, and stick with a healthy balanced diet, exercising regularly, getting enough sleep, and socializing with your friends.