Vitamin D
Vitamin D is one of my four foundational supplements for optimum health (the others include a multi vitamin, omega-3 and vitamin K2). Vitamin D is critical for the immune system. Low levels of vitamin D have been associated with 22 different forms of cancer (especially colon cancer), depression, multiple sclerosis, gum disease, muscle weakness and more. I generally recommend Vitamin D3 (from fish or lanolin). Vitamin D2 is synthetic, and may not be as well absorbed. - Nathan Zassman
Related Reading (particularly for vegans): Info on Vitamin D from Non-Dairy Sources
