The ongoing debate about what vitamin D can and cannot do for you makes it hard to know if it's smart to take D3 as a supplement. (It is.)

You've probably heard that studies show it doesn't reduce asthma attacks or statin-induced muscle pain, or prevent fractures associated with osteoporosis.

On the other hand, solid studies do show it helps your body absorb calcium — protecting you from osteoporosis — helps muscle and nerve function, bolsters the immune system, and protects you from autoimmune diseases.

A new study offers yet one more important contribution it can make to the 8 million folks in the U.S. who have psoriasis. Research out of Brown University's medical school found that people who have the most widespread psoriasis have the lowest blood levels of vitamin D, and those with the least amount of psoriasis have the highest levels.

It appears that vitamin D has an impact because it affects the body's immune response and has a direct effect on cells involved in skin repair. 

Everyone's target blood level of vitamin D is 50 nmol/L or higher (but never above 110 nmol/L). Because of indoor lifestyles, use of sunscreen, and less than perfect nutrition, you might consider having a blood test to check your level of vitamin D.

I recommend a basic supplement of 1,000 IU of D3 (under age 65) or 2,000 IU (65+) daily until your doctor determines what you need to attain an optimal level.