Are there any dietary supplement to help with psoriasis?!

Are there any dietary supplement to help with psoriasis?

I have severe psoriasis of the scalp and regularly use a coal tar based shampoo but it doesnt seem to be working lately. I have used it for years and it usually keeps the psoriasis pretty much under control. I dont know why I seem to only have it in my scalp with just a few spots on other parts of my body.

I have suffered with psoriasis on my knees and elbows for the last 17 years, the patches have always primarily contained themselves to my knees and elbows. However, I was working a job next store to a Mcdonalds restraunt for a while, after eating the food there 5-7x a week (lunch, whatever....) My psoriasis *exploded* I began developing patches everywhere, hands, feet, face, torso, legs, back of knees (painful!). I cut the Mcdonalds out, and within a week the outbreak recessed, and dissipated except for the patches on my knees and elbows Ive always had. Needless to say Ive eliminated Mcdonalds from my diet.

I don't know what they put into the food there, but it acted as "super-growth fertilizer" to mine, I had severe patches places where I never had before, and my existing patches were unreal.
I don't know anyone else with psoriasis, so I am unsure if the food there affects others this way, it may be something to consider however if you have eaten at McDonalds lately....

Good Luck