from my research, i consider 1000 mg dy a bare minimum. i take that everyday when i'm out in the sun with my shirt off,as my skin tolerates the sun well (the incidence of melanoma in the Scottish islands(cold) is 10x higher than the mela. rate in the south coast of france- the sun worship capitol of europe).i take 4000mg when it's cloudy and i have my leukemia buddy on 10,000 mg day as recommended by dr. Rowen and also Life Extension Foundation. if you are one of those mainstream media believers that hide from the sun, you're going to get sick.