I don't have a Vit. D problem, but I hear its very common for women as you get older. If it does turn out you have a deficiency, your doctor will recommend supplements, vitamins or even medications but my gf who is a nutritionist recommends curing it with food.
Here are her suggestions:
The hands-down best way to get vitamin D is from high-vitamin cod liver oil
an old-fashioned supplement considered a "sacred" food by many traditional cultures around the world (or fish liver oil of other kinds as well). The fermented variety is even more packed with nutrients, enzymes, etc. Order from www.GreenPasture.org -- Dave (the owner) uses cod livers from Norway that are going to be discarded, and ferments them the traditional way in large vats. He tests every batch for purity (no mercury, PCBs, etc.) but does not deodorize, water down, or otherwise process the oil in a way that renders it less beneficial. He has done a LOT of research on this and is deeply committed to providing an unusual and extremely high-quality product.
Also, contrary to popular opinion (including medical opinion), it is very
important AND NOT THAT DIFFICULT to get vitamin D from your diet. Unfortunately, it will be next to impossible to get it in a vegan diet, and quite difficult to get in adequate amounts from a vegetarian diet. Of course, I have no idea what your diet is like -- most Americans eating a general American diet also don't get much D. This is because it is formed and stored in the bodies of animals who are --much like us!-- exposed to sunlight, and eating natural diets of grass, bugs, small animals, plankton, etc. (And let's face it: most of the animal products we eat now are from confinement-feeding operations, or fish farms --NOT nutrient-dense sources.) Animals form vitamin D in their fur, feathers, and
skin when exposed to natural amounts of sunlight (so a "free-range" chicken egg from the store won't cut it - the chicken must be on pasture). Vitamin D is also a fat-soluble vitamin, so we have to eat FAT to get it!
It is found in fish liver oil, fish eggs, liver & other organ meats, egg yolks
(from chickens roaming on pasture), butterfat (butter & cream) from milk of cows on pasture (remember, they have to be out in the sun most of the time), small oily fish & shellfish, duck & chicken fat (including the skin!), and -last but not least- fat from pigs on pasture. One tablespoon of lard or bacon fat from a truly pastured pig will give you a whopping 1100 IUs of vitamin D. Now THAT'S not something they talk about in any doctor's office! :)
Since I began eating a diet containing these foods about 1.5 years ago I have watched every health problem I had disappear: hypothyroidism, hypoglycemia, low energy, acne, PMS, joint pain, headaches, mental fogginess, irritability & moodiness...the list goes on. Oh, and I'm back to my teenage weight, about 100-105 lbs. So eating all this fat (paired with lots of vegetables and high-quality protein) has certainly not resulted in weight gain!
Hope that helps! Good luck!