Increased muscle mass and recovery? Stronger bones? Improved immunity? Does any of that interest you? Although widely agreed that sun exposure is the preferred method of obtaining Vitamin D, using even conservative numbers, at least 25% of the U.S. is deficient. Combine that with the fact that those numbers are calculated using a maintenance dose not what you need for the aforementioned, it is probably safe to say you could use more. This, coupled with chances of dosing too high being extremely minimal mean anyone interested in performance should experiment with the D.