As far as I am concerned Vitamin D3 is essential to life. Vitamin D3 is essential to our metabolization of calcium. Our bones benefit, our nervous system benefits and our mood benefits. Don't be deceived by anyone who says D2 is a phyto-analog to D3. It is not. Natrol does a good job with this D3 supplement. I good high dose at a good price. I feel much better when I remember to take my D3 and so do many of my friends. It is important to be consistent or your results will not be as good. *If you are Kosher then find a vegetarian form of D3. D2 only mimics D3. Research has shown that D2 stops working half way through the metabolization of Calcium. A person can ingest D2, thinking that it is Kosher, and still end up with osteoporosis, rheumatoid arthritis, depression, Kidney stones and other calcium deposits all over the body. I don't think Divine Being wishes us to be so crippled, depressed or otherwise impaired so I stick with D3 exclusively and avoid D2 like the plague