A recent meta-study (a study of a number of existing studies) finds that certain vitamin supplements appear to shorten the lifespan of those taking them (specifically beta-carotene and vitamins E and A.)
Assuming the findings are accurate, and assuming that we are in a fortunate enough situation to have access to sufficient food (which large portions of us are not), then this is another reminder eat a balanced and varied diet of fresh food rather than relying on supplements.
It is usually not a good idea to provide the body with substances it did not evolve to handle, and dietary supplements mostly fall into this category. A balanced diet does provide whatever nutrients the body needs, and a modern balanced diet is nutritionally far beyond what our ancestors - in most cases, had access to, and their bodies still did quite well - as we are living evidence for.
As with health related issues in general, the answers are often quite simple - and found when we look at the lives of our ancestors. They ate a varied (omnivorous) diet when possible, ate in moderate amounts... often by necessity, the food was organic and local, and they engaged in a variety of physical activities throughout the day. The closer we are to this, the more physically healthy we are likely to be.
It is very simple. Yet, if there is something about it we don't like we look for shortcuts, such as dietary supplements, which may not work or have unforeseen effects.
More about the study on BBC: Vitamins 'could shorten lifespan'