Vitamin D3 is not only helpful with your mood but it also supports your immune system and have other benefits.
The best way to obtain the vitamin D (which is a steroid hormone by the way) is from the sun. This is why you see many people getting what we call seasonal depression during the winter when sun exposure is reduced which means vitamin D levels are reduced.
Personally I take 2,000UI a day and when it's sunny outside and i get sun exposure I just skip. Anyway Vitamin D got a long half-life and is supposed to stay in your system for a while. Some people like to take huge amount once a week, some other take small amount once per day.
1,000UI is a good starting dose and I'm sure it will help you. 2,000UI is the dose you should take during the winter. Anyway don't take it when you go at the beach for example since it would be useless.
Balacing your D levels should happen really fast. I would say 1 month until you can see a difference.
For more info you can google luminitherapy too.
I have been dealing with depression it seems like from birth. At 16 I was tested and diagnosed with depression and was put on Zoloft. Sure it helped.
When I got married and decided to have children I didn't want to be taking medication during my pregnancies. I informed my doctor that my depression was at it's worst during winter months and she informed me it could be due to lack of vitamin D. So I decided to take vitamin D3 1000 iu and it really has been helping me. I would really recommend it to anyone dealing with depression.