July 26, 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.

Who is at risk for vitamin D deficiency?

Research has begun to focus on who is deficient or insufficient in their vitamin D levels. Finding a deficiency does not mean that vitamin D is the cause of any ongoing symptoms. It simply means that there is a possible relationship, and more studies need to be done to clarify the relationship between vitamin D insufficiency or deficiency and disease processes.


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

Crohn's disease: A recent analysis of 63 studies on Crohn's disease (CD) found that there was a 57.7% prevalence of vitamin D deficiency in CD patients. They also found that the more severe the CD was, the lower the circulating vitamin D levels were.

Bariatric surgery: A review of 30 studies on patients undergoing Roux-en-Y gastric bypass and vertical sleeve gastrectomy found that preoperatively vitamin D deficiency was found in 13%-90% and insufficiency was found in up to 98%. The levels remained the same postoperatively. The research has shown a high level of insufficiency and deficiency levels in pre- and post- bariatric surgery patients, but no consensus has been established for the adequate dosage of vitamin D for prevention and treatment. The only way to know if the treatment is working is continued follow-up with your physician. The baseline vitamin D levels were lower in the African-American group, but all of the patients were able to achieve normal levels with comparable supplementation.


Elderly: 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.

Children: A study done in Ethiopia found that schoolchildren between the ages of 11-18 years were more likely to be overweight or obese when they were deficient in vitamin D. Another study of 301 students aged 11-19 years found that 12% of the students were deficient, and 53% had insufficiency. It also found that as body weight increased (measured by BMI) the level of vitamin D decreased.

Rheumatoid arthritis: A recent analysis of studies done on 1,143 patients with rheumatoid arthritis (RA) found that vitamin D levels were significantly lower in patients with RA compared to those without.

Fibromyalgia: The exact relationship between low vitamin D levels and fibromyalgia (FM) is unknown at this time, but there is an increased deficiency risk in people with FM. In a study of 150 patients with FM, 93% had deficient levels of vitamin D. In another study of 103 patients with FM or muscle pain, 75% had low vitamin D levels. Treating the deficiency resulted in 90% of them having improvements in their pain. The benefit on long-term bone health and muscle strength and the improvement in depression that can be found with treating vitamin D deficiency are all important for patients with FM and make it an important test for anyone with FM.

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 6/9/2016