If you live in the North, above 40 degrees latitude, you should consider adding this product to your regimen during the winter months or times when you have not been able to get any sun on your skin for several days. Being a raw, vegan source of Vitamin D3, I feel the effects of this product almost immediately when I am deficient. We all know that feeling... sometime in December or January when we haven't seen the sun in weeks... it is responsible for Seasonal Effective Disorder (SAD), feelings or lethargy or tiredness, etc. I find that 1-2 capsules of this Vitamin D relieves some of that lethargy within minutes after ingestion. According to traditional practices, the other main source of Vitamin D during the Cold northern winter months is fatty Cold water fish, such as salmon or haddock. If you are vegan, or simply lack the fish to provide this Vitamin D, this supplement can be a lifesaver. Highly recommended