Hi Lulu,
I, too, am very deficient in Vitamin D.
The upwards limit is listed as approx 3,4000 IU/day. However, Vitamin D is a hormone and not really a vitamin, so any supplementation will be determined by
- what your levels are presently/when it was measured - your age and state of health (any fat absorption issues, autoimmune disease, past calcification issues, do you take blood pressure meds etc.) - the latitude of your residence - the shade of your skin and so on. I personally would not recommend going ahead with supplements until the need and particular amount is determined. That's just my opinion.
For now, I'd say get yourself some unscreened sun for 12-15 minutes a day after 12:15 pm (this long with not accelerate photoaging, skin cancer etc.) and include whole foods (more bioavailable Vitamin D) in your diet that either help with the absorption of Vitamin D (mushrooms, especially shitake) and ones that are rich in Vitamin D like ghee/clarified butter (if you are not veg. This is also rich in Vitamin K which will help absorb magnesium. Magnesium also helps with Vitamin D deficiencies. It is all connected.
), egg yolks, dairy - especially cultured things like grass fed kefir, oily seafood like sardines. Some folks like to go ahead and take cod/halibut liver oil or krill oil as a whole food Vitamin D source. I would not recommend this as these substances are also
very high in Vitamin A. Too much in a healthy individual without the need for Vitamin A supplementation will interfere with the absorption of other vital minerals (not advised for Vitamin D imbalances) and be too taxing on the liver.
I, myself, am considering trying transdermal Vitamin D as I am eating plenty & supplementing (by direction of an endo) and it is still a little low. It has only increased minutely as of late. In my case it is due to other autoimmune conditions in my body. Transdermal/topical magnesium has helped me quite a bit with sleep cycles, so I am thinking I may respond well to Vitamin D this way as well. For winter mood disorders like SAD, there are some ladies here in the forums who have been doing quite well with special lamps.
http://cathe.com/forum/threads/sad-light-therapy-box.301229/