A claim that vitamin D can increase longevity reminds me of the enthusiasm some folks had concerning the marvelous powers of vitamin E.
There is a very favorable ( almost glowing) report in Internal Medicine News (Feb 13,2008) (ww.internalmedicinenews.com) that outlines some of the more favorable evidence regarding D.
A meta-analysis from AIRC analyzing 18 RCTS with over 57,000 subjects indicated a 8% mortality reductions in those subjects in trials that lasted 3 or more years.
A telomere length analysis in 2,160 female twin pairs found that those with the higher Vitamin D levels versus those with the lowest Vitamin D had longer white blood cell telomere lengths. This difference was said to be the "equivalent" of five years of aging. Telemeres are the ends of chromosomes ( likened to the little plastic tips on shoe laces) that are known to shorten with each cell division and have gained some reputation as a type of surrogate maker for aging. Here is a good explanation of how that shortening occurs.
Dr. Robert Vogel of University of Maryland spoke highly of the potential benefits of Vitamin D and made the point that from the results of the Harvard Alumni Study being thin as you age and have a moderately vigorous exercise program as you get older seemed to increase longevity by about 6 months each. Well, taking a pill or two a day is easier than that, right.
Claims of anything being a fountain of youth pill deserve a very high level of scrutiny but I'll bet sales of D are going up. I'll admit I was surprised and then later accepting of the studies that demonstrated fewer falls in the elderly on D supplementation which seem to work by increasing strength. To say that you can increase your life by five years is over the top and too enthusiastic an extrapolation but I'll have to say that I have increased my Vit D dose from the previously generally recommended 400 u to 1000.