Do anyone take vitamin D3 and could tell me why? What effects it have for you?

It is critical for your bone health:

http://www.webmd.com/diet/vitamin-d-deficiency

I take 3000 units a day, but I also have blood work every six months. D3 is stored in fatty tissue, and as you lose weight the amount of D3 units you require may decrease. Too much D3 can be toxic, but I think we're talking in the 100,000 unit range. Your doctor is the best to advise how much you should be taking.

I am currently on 5000 IU a day, due to mine being VERY low. My weight loss has plateaued for the last couple of months and he said this could be the reason. According to research our bodies need Vit D to tell our fat cells to release fat instead of store fat.

Low D can also effect everything from our heart to our bones due to Vit D being needed to absorb Calcium. Both our bones and muscles need Calcium to function properly.

So I am on this high dose for 3 months and then I go back in to have it checked and will go from there.

OK I started a small dose myself 400iu because I felt my getting to tired quick I felt aches and my body I tried vitamin b12 it didn't work I felt drained too

Don't take this as medical advice, but my doctor told me to take the D3 supplements based on my blood tests prior to surgery. He advised that 400 units wouldn't touch the low numbers, and that I should take at least 2000 units a day. I wouldn't advise you to take the supplement in larger doses unless a doctor tells you to--but that is what I had to based on my tests.

My calcium has D3 included. D3 is needed to help the body absorb calcium.