I really notice a huge difference with taking this Vitamin D3. I am low on vitamin D - scored 27 and am always tired, moody and get Anxiety and depression. Doesn't help that I live in Washington State. This is one of the most important supplements and one that I can say for sure I notice an immediate difference. My doctor told me to take 4000 IU a day so i just take two soft gels a day, since they don't offer one with 4000 IU - the only downside. But I really recommend Vitamin D3 if you are suffering from any almost anything - especially low energy and mood disorders. It is the #1 supplement and most people are deficient