Upon receiving the SOLGAR Vitamin D3 5000 IU, I start taking one capsule daily as suggested. three weeks later I can feel my teeth are getting much stronger. I don't know if my bones and teeth are really getting stronger, but I feel like I will chew any food that feed in my mouth. However, here are the side effect I am experiencing. After three weeks of continuously taking one capsule each day. I felt I was stressed out for no reason even thought I didn't get any addition stress from work or my surrounding, but I felt like I lost interest in doing anything. I lost my appetite for food. I felt very tire all the time. I couldn't wait to hit the bed every night. that went on for two weeks. I start realized that something is wrong because I consider myself a very healthy person. I am 41 years old. I workout twice a day, five days a week . I out run most people half of my age. I love to eat and I had been in very stressful situation before, but don't I remember when was the last time I lost my appetite for food or felt tired for two weeks in a row ever. After doing some research on the internet for Vitamin D side effect. I stopped taking this product. within a few days, all the symptoms clear away. I start to enjoy doing whatever I did, the food taste delicious and I start feeling energetic again. just to be sure that it was the vitamin D that cause all these side effect. I retake this product after two weeks of discontinued. the same side effect coming back within a few days after taking this product