I've never had the D levels checked. I take 5000 iu's a day as it seems to be the recommended median dose from things I've read.
Mike Adams at naturalnews.com has one of the best articles I've seen on astaxanthin. I actually got my endo surgeon, the senior oncologist at my cancer care center, my primary care and my son on astaxanthin, coconut oil & green tea. My son says, at 21, weight lifter, that since he started the above a month ago he has never felt better, slept better or had more energy then he's had with these supplements.
Puritans Pride, iherb.com or Vitacost has the best sales on the herbs, Amazon has the best on the 54 oz. solid virgin Nutiva coconut oil at 25.00 and change + free shipping.
I just found my skin is better with 12 mg. day on the astaxanthin. And be sure to get at least 3 tbsp. day of the oil.....a google on the oil brings up all kinds of benefits. Here's a Dr. Mercola from yesterdays newsletter:
Fatigue, Dry Skin, Gaining Weight? See Why You'd Better Check Your Thyroid! - articles - articles.mercola.com