I've been "down" for some time, sometimes badly so. I went to see a doctor about it, and she had a blood test done for vitamin D levels. She called today and my vitamin D level was 18.6 out of a minimum of 30. I'm taking 1,000 IU of vitamin D3 twice a day and it might be helping already. The doc told me that most people in the US and Canada don't get enough vitamin D from either sunlight or food. Others might ask their doc for such a blood test.