First you need to look at this chart. Vitamin D incidence prevention
What you see are some of the problems that Vitamin D is involved in.You also see the level that's needed in your body to get these effects. The level needed is 60. Now the bad part, if you are like most people you are probably around 25. Here's the problem, you get Vit D from the sun and most of us don't get enough good sunlight to get a healthy dosage. The fact is that is we live in a temperate zone on the planet, the angle of the sun striking our skin does not allow us to get enough Vit D. If you're dark skinned, you are seriously screwed.
I live in Michigan and it is known that if you live above Atlanta, Georgia there is no way to get enough sunshine in the winter months. Fair skin helps here. Sunlight hitting fair skin rapidly creates Vit D. Fair skin is a necessity in the north or south temperate regions. This is because the colder temps force people to cover up to preserve body temperature. This means the sun has less surface on which Vit D can be created. Being pale is an advantage here. Being dark, however, means that you will almost never get the needed Vit D, if you live in a cold climate.
This isn't a problem. You can go out and buy Vitamin D at your local drug store and make sure it's Vitamin D3 and not D2. Get the 2000 IU version, take two little pills a day and you should at least get up to 30 or 40. If you're, like me, dark skinned then taking 4 pills a day would get you up to 70 or 80. Who knows, this could change your luck.
PS If you continue to eat wheat, you might need a lot more since wheat, for whatever reason, tends to be antagonistic to Vitamin D.