I don't spend much time outdoors (I work from home and mostly at nights to deal with our offshore team - I work for pharmaceutical company) and my vitamin D levels have been very low for several years. I tried prescription for vitamin D (D3) but that did not help even after costing a lot in co-pays. I finally did thorough research on this and bought this product. I have been on it for almost 3 weeks now. I started feeling better in about 4 days after I started taking it. I have chronic Insomnia for about 15 years now. I went to specialists, tried sleep medications, had two overnight sleep studies, used varieties of devices, nothing helped. I also take multiple medications which add to the problem. As I work at night which compounds the problem, it has been more severe in recent years. Four years back, I could not sleep even 10 seconds for 8 continuous days and nights and had a seizure and was hospitalized. I had many severe health issues because of this problem. However, I sleep somewhat better now (about 3-4 hours a night) . It needs to be even more better and I hope it will be, after taking regularly for some more time. I will check my vitamin D levels in my next blood test. I also feel better as I am less anxious. I am thinking of taking melatonin supplements too to improve my sleep further. I tried these in the past but they did not help at that time. I am hoping that they will work now with the combination of this product. These are easy to swallow softgels. There is no after taste. Small size. After reviewing many products, I found doctor's best to be having excellent dosage per serving and is also sold at extremely reasonable price. 5000IU has been good dosage for me