May 24, 2016

Vitamin D Deficiency

What causes a vitamin D deficiency? (Continued)


Being overweight or obese may put you at risk for a vitamin D deficiency. A study done on 2,187 overweight and obese subjects found that those with a BMI above 40 had 18% lower serum vitamin D levels than those with a BMI under 40. Another study compared the vitamin D levels of 154 obese subjects to those of 148 nonobese subjects and found that the obese subjects' vitamin D levels were 23% lower. While diet and decreased sun exposure may have some impact on this, there appears to be an increased need that cannot be met without a supplement. One study tested the blood levels of vitamin D after sun exposure in both obese and nonobese subjects. Both saw an initial rise in vitamin D levels after similar exposures, but 24 hours later, there was 57% less vitamin D in the blood of the obese subjects. Both groups had a similar capacity of the skin to produce the vitamin. The difference was seen in the release of vitamin D from the skin into the circulation. It is believed that the fat under the skin holds onto the fat-soluble vitamin instead of releasing it, but more research needs to be done to confirm this. It is also not clear if weight loss causes an increase in vitamin D levels due to the fat cells releasing it into circulation. Some studies have shown small increases and others have not. Those who are losing weight should discuss the impact this may have on vitamin D levels with their health-care provider. For those who wonder if a vitamin D deficiency can contribute to weight gain, so far one study tested this and did not show this to be the case.


People with one of the fat malabsorption syndromes (for example, Crohn's disease, celiac disease) and people who have had bariatric surgery are often unable to absorb enough of the fat-soluble vitamin D.


It has been shown that as we age our body has a decreased ability to synthesize vitamin D from exposure to the sun. There can be as much as 25% reduced production over the age of 70. While this can have an impact, it doesn't cause as much of a deficiency as the other risk factors.

Medications and medical conditions

A wide variety of medications, including antifungal medications, anticonvulsants, glucocorticoids, and medications to treat AIDS/HIV can enhance the breakdown of vitamin D and lead to low levels. There is also a loss of vitamin D for those with chronic kidney disease, primary hyperparathyroidism, chronic granuloma-forming disorders, and some lymphomas. Continue Reading

Reviewed on 2/26/2015