I try to take enough vitamin D(Need to take blood test to test for what is appropriate level for yourself)-much higher than RDA recommended, not enough to depend on the sun, take a supplement, for strong bones and prevention of cancers. Usana supplements have higher levels of vitamin D added to their supplements and good multiple vitamin set with vitamin D as well. I also make sure I take enough omega 3 oils and calcium. In total, my vitamin D is about 3100 IU daily. Research shows a daily oral intake between 1,000 to 4,000 IU of vitamin D (depending upon your baseline vitamin D blood levels) is ideal. Vitamin D toxicity does not occur until blood levels reach 150 ng/ml or more; which would generally take an oral dose of 50,000 IU per day! Vitamin D status can be assessed by a blood test. Be careful about the lab’s reference ranges, because sometimes they will compare you to the "normal population," which is DEFICIENT...you don't want to be “normal” (or deficient in vitamin D). Optimal levels of vitamin D3 (25-hdroxyvitamin D) should be in the range of 30 – 50 ng/ml (or 75 – 125 nmol/L). What is fascinating, and critical for you to know is that there are well over 89 medical studies showing that high vitamin D blood levels (which can only be obtained by supplementing with more than 400 IU/day) reduce nearly all cancers, including cancers of the colon, rectum, breast, and prostate (some as much as 50%). Furthermore, vitamin D has been shown to suppress inflammation by reducing cytokines (inflammatory modulating molecules). Thus, taking at least 1,000 of vitamin D or more per day helps protect against inflammatory conditions such as rheumatoid arthritis, chronic muscle pain (fibromyalgia), congestive heart failure, diabetes, stroke, and mutliple sclerosis. God bless you all.