Re: What are underlying causes that contribute to low Vitamin D?
I also am fair-skinned and avoid the sun as much as possible. When I lived in sunny central California, I used to get depressed every winter. Then I moved to grey cloudy northern Germany, and the winter depression got more intense every winter and lasted longer each year until I became suicidal. I finally doscovered Vitamin D3 supplements (cholecalciferol), and no longer have suicidal depression in the winter.
In addition to the lack of sunlight on the skin, as aussiejono says, there are a few other possible causes for low Vitamn D.
It is a fat-soluble vitamin, so obesity can take up any vitamin D into the fat cells and make it unavailable for active use by the body.
There may be insufficient fat in the diet, so that even though one is getting plenty of sunshine or getting Vitamin D in supplement form, it cannot be utilized.
As we get older, it means that the skin and kidneys are not as able to convert Vitamin D to its active hormone form for use by the body.
There are diseases of the parathyroid gland, liver, and kidney that can affect the body's use of the vitamin.
Other medical conditions that affect vitamin D utilization include pancreatic enzyme deficiency, Crohn's disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease.
Some medications can affect the absorption or utilization of Vitamin D. Some of these are anticonvulsant meds, some cholesterol lowering meds, meds that reduce hydrocloric acid release in the stomach, corticosteroid drugs that treat autoimmune and inflammatory diseases such as asthma, rheumatoid arthritis, and ulcerative colitis, and Heparin used as an anticoagulant med.
There are some theories that too little iron in the diet can result in a deficiency of Vitamin D.
I hope that you are able to increase your Vitamin D level. It affects so many functions in the body, not just depression as it did with me. If you take supplements, it appears that the form D3 (cholecalciferol) is more easily utilized by the body than the form D2 (ergocalciferol).
I hope this helps.