Supplements should only be prescribed by doctors and levels should be monitored regularly. The dangers of taking a hormone without the supervision of a doctor let alone from unverified/untested sources should absolutely avoided. 

Vitamin D toxicity is commonly caused by unsupervised doses of vitamin D supplementation — and not by diet or sun exposure. That's because your body is able to regulate the amount of vitamin D produced by sun exposure and from foods. 

Vitamin D is also fat soluble. Unlike water soluble vitamins or hormones, if you take too much it does not get dispelled when you pee. Rather, it accumulates in your fat deposits and stays there. Hence the build up and eventual toxicity. 

Too much vitamin D in the blood causes abnormally high levels of calcium to circulate in the blood. This will damage bones, tissues, and other organs. It can also lead to high blood pressure, bone loss, and kidney damage if not treated. 

As many as 1 billion around the world are feared to have a Vitamin D deficiency. Peer reviewed studies have shown 50% of the world’s population do not produce as much of the vital nutrient necessary to keep teeth, bones and muscles healthy. It’s a problem that can affect anyone at any time, but the issue is more pronounced for people who are unable to get enough sunlight.