Concerning particle size and heart disease, while I have not reached any personal conclusions, Niaspan will alter the particle size towards a favorable pattern. However Niaspan does nothing to prevent heart disease, heart attacks or strokes.View Thread
While I do not consider myself an "expert", I have studied vitamin D for a basic understanding. I can shed some light on the basic principles.
The primary source for vitamin D is from sunlight. The sun shines on a cholesterol component within the skin layers which triggers the process of making vitamin D. The angle of the sun is important. Mostly between 10am and 2pm produces the most vitamin D. Also your latitude is important. You want your shadow to be no more than half your height to achieve the best results.
The natural pigment of your skin will also be a factor. Lighter skin makes D faster, while darker skin makes D slower.
Foods that provide vitamin D are oily fish like salmon, and Dairy products.View Thread
For those who follow particle size, there are some things you can do with diet to change particle size to the large fluffy ones. Its been a while since I read the data from, I believe it was the American Journal of Clinical Nutrition, or something like that. I want to say it was eliminating wheat would go a long way in changing particle size. My memory is foggy on this one, but I do remember they proved it can be done with diet.
Although I have given up on cholesterol levels themselves causing atherosclerosis, I am still open minded on the particle size theory, but not conclusive.