Discount brokerages require a minimum age of 18. However, you can create a sub-account under your dads name (as long as he signs some sort of consent form) and these sub-accounts don't have a minimum age requirement.
Vitamin D deficiency rickets can be caused by a lack of vitamin D in the diet, a lack of exposure to the sun, or malabsorption syndromes in which there is an inability of the intestines to adequately absorb nutrients from foods.
The study also failed to identify other potential causes for vitamin D deficiency. In humans, heart disease is associated the patient fitness and amount of body fat. Vitamin D is fat soluble and can be isolated in body fat and reduce blood levels.