My Dr. told me to start taking vitamin D every day a few months ago. He gave me a shot of Vitamin D first. I didn't feel bad before but I have a much better feeling good feeling now. And I have noticed I sleep better. I take 20,000 units a day sometimes more if I'm not out in the sun for any length of time. I buy the 5,000 unit gel caps. I've been reading about Vitamin D studies and it's really amazing. Kids who don't play outside in the sun for a few hours every day need lots of vitamin D. Teens need a lot of it along with calcium. No adverse reactions to Vitamin D has ever been reported. It's cheap so ask your Dr. if it will benefit you to take Vitamin D.