The ten most important things you need to know about Vitamin D, with AITD or not:

Vitamin D is not really a vitamin. Vitamin D is a fat-soluble steroid hormone precursor that you get primarily from either sun exposure or supplementation. A very small amount comes from a few foods we eat.
Vitamin D has been known for its contribution to the maintenance of normal levels of calcium and phosphorus in the bloodstream. Current research has discovered that vitamin D levels can also impact a wide range of health issues, such as:
Cancer (Breast, Ovarian, Colon, Non-Hodgkins Lymphoma, Kidney, Endometrial, Prostate)
Type 1 Diabetes
Fractures/Osteoporosis
Pregnancy Complications
Multiple Sclerosis
Cardiovascular disease
High Blood Pressure
Asthma
The vitamin D that you take into your body is changed by your liver into a substance called 25(OH)D. Vitamin D (25 (OH)D) is usually measured on a scale of 30 – 100 ng/ml. Below 30 is commonly considered deficient.
To determine whether you need to supplement vitamin D, you should test your vitamin D level by doing the 25-hydroxy D lab test, which measures 25(OH)D. The Vitamin D Council recommends testing every 3-6 months when you’re trying different regimens to figure out how much vitamin D you need to maintain your optimal level.
The optimal level of vitamin D is a matter for debate. The Vitamin D Council suggests that “a level of 50 ng/ml is the ideal level to aim for, with a range of 40 – 80 ng/ml.” And there used to be mention that ideal is 60 – 80.

The Vitamin D Council recommends taking vitamin D3 rather than vitamin D2. Vitamin D3 is the type of vitamin D naturally produced by your body in response to sun exposure, while vitamin D2 is not. In the United States, most over-the-counter vitamin D supplements are D3. Other than that, it doesn’t matter what form of vitamin D you take, whether it’s in a capsule, tablet or liquid. For most people, vitamin D is easily absorbed in the body and you don’t need to worry about what time of day you take it or whether you take it with meals.
Vitamin D is fat-soluble, which means your body has a hard time getting rid of it if you take too much. The Vitam