Four year old thread... but...
The RDA is based on what the average person needs to stay "not sick." I don't want to just be "not sick," I want to be in optimal health.
The RDA is based on the average (i,e, sedentary) adult. We, as runners, destroy more muscle tissue, rebuild it, and put our bodies under more extreme physical stress in one week than the average person will do in years. It makes sense that high-level exercisers would need more nutrients than a couch potato, but the RDA doesn't factor that in.
As we get older, the body's ability to utilize nutrients declines as our cells become less efficient. One remedy is to make sure the body always has a surplus of nutrients to do its job.
Overwhelmingly, people do not eat healthy.
It's hard to get even the lowest RDA of some vitamins in a normal diet. Take vitamin D, for example. You'd have to eat 15 egg yolks, 300 glasses of 2% milk, 5 glasses of whole milk,1 serving of wild caught salmon, 3 servings of farmed salmon, or two tins of tuna to get the RDA. Other than the people who drink large amounts of whole milk, who does that!!!??
I take over 2 dozen supplements every day. I tend to avoid hard pills so it's almost all capsules and gels. When I had to go off my supplements for two weeks prior to surgery in April and again in July, I could feel the difference... loss of energy, aches and pains, tiredness.
I suspect that the studies showing increased disease among those who take vitamins would find that many of those people do NOT exercise. Surprise! Supplements aren't magic pills. They work in conjunction with exercise, sleep, lack of stress, good diet, and weight management to promote good health.