Vitamin D and Fibromyalgia
Vitamin D works to help the body absorb calcium, which is essential for strong bones. Individuals who are deficient in vitamin D for prolonged periods may develop thin, brittle bones. This condition is commonly referred to as rickets in children and osteomalacia in adults. In older adults, vitamin D also helps to protect against the development of osteoporosis, which is the gradual thinning of bone tissue and loss of bone density. In addition to its bone-building properties, vitamin D is also essential to a number of other functions in the body. It aids in muscle movement, transmission of nerve signals between the brain and the rest of the body, and helps support a healthy immune system.
Vitamin D is not naturally abundant in foods. The best sources of vitamin D include fatty fishes such as salmon, tuna, and mackerel. Foods such as beef liver, cheese, and egg yolks contain small amounts, as do mushrooms. The best dietary sources of vitamin D include those foods that have been fortified with the vitamin, such as milk, certain breakfast cereals, orange juices, yogurt, margarine, and soy-based beverages. In addition to dietary sources, the body produces vitamin D when skin is exposed to sunlight; however, filtered sunlight (i.e., that which comes in through a car or other window) will not produce vitamin D. Furthermore, darker skin color also reduces the amount of vitamin D that the skin is able to produce.
Many Americans are deficient in vitamin D. The most accurate measure of one’s vitamin D level is obtained by withdrawing a small sample of blood and measuring the level of 25-hydroxyvitamin D. Levels below 30 nmol/L (nanomoles per liter) are too low for optimal bone or overall health, and levels above 125 nmol/L are too high. Levels above 50 nmol/L are optimal for most individuals. Blood levels of 25-hydroxyvitamin D tend to decrease with age and males generally have higher levels than females. Non-Hispanic whites tend to have the highest vitamin D levels of any race and non-Hispanic blacks the lowest. In addition, other groups of individuals may not have adequate vitamin D, including breastfed infants, older adults, dark skinned individuals, individuals with digestive diseases such as Crohn’s disease or celiac disease, and individuals who are obese.
The safe upper limit for vitamin D intake is 4,000 IU (International Units)/day for adults and pregnant and lactating teens and women. Although toxicity is uncommon, high blood levels of vitamin D can be harmful. Signs of vitamin D-related toxicity include nausea, vomiting, decreased appetite, constipation, weakness, and weight loss, as well as kidney damage in extreme cases. In addition, excess vitamin D can cause confusion, disorientation, and heart rhythm disturbances by raising blood levels of calcium. Vitamin D toxicity almost universally results from overuse of vitamin D supplements.
Individuals who take vitamin supplements should also be aware of potential interactions with several medicines and supplements, including prednisone and other steroid medications, certain weight loss drugs, cholesterol-lowering medications, and certain anti-seizure drugs.
Vitamin D and Fibromyalgia Research
A substantial body of research has examined the presence of vitamin D deficiency among fibromyalgia patients, and little evidence has been found to support an association between the two. (Daniel & Pirotta, 2011).
Huisman et al. (2001) examined the blood levels of 25-hydroxyvitamin D as well as parathyroid hormone in 25 female patients with systemic lupus erythematosus and 25 female patients with fibromyalgia. The researchers found similar levels of 25-hydroxyvitamin D between both groups, although both groups were determined to be deficient in vitamin D. More recent studies have also failed to find differences in vitamin D levels between fibromyalgia patients and health controls, or with other patients who suffer from chronic pain conditions. A 2010 study by Bhatty et al. evaluated the vitamin D levels in 40 female Pakistani fibromyalgia patients. All patients were diagnosed with fibromyalgia according to the American College of Rheumatology (ACR) diagnostic criteria, as well as through the exclusion of other potential diagnoses through physical examination. Blood levels of vitamin D were measured for all participants. The researchers found that 80% (32 out of 40) of the participants had deficient blood levels of vitamin D, whereas the remaining 20% (8 out of 40) had insufficient levels. Despite the small sample size of this study, the authors note the need for future population-based studies that include not only healthy subjects but those without a diagnosis of fibromyalgia who have musculoskeletal pain.
An Iranian study from 2010 evaluated blood levels of 25-hydroxyvitamin D in 276 patients with either nonspecific skeletal pain or fibromyalgia, as well as 202 control subjects. The researchers found that those individuals with nonspecific skeletal pain had significantly lower 25-hydroxyvitamin D levels than controls. In addition, they found a significant positive association between 25-hydroxyvitamin D deficiency and skeletal pain. However, no association was found between 25-hydroxyvitamin D levels and fibromyalgia, however (Heidari et al., 2010).
Another study from 2010 also failed to find any association between blood levels of vitamin D and fibromyalgia. This case-control study examined the blood levels of 25-hydroxyvitamin D in 87 patients with a confirmed diagnosis of fibromyalgia (based on ACR diagnostic criteria), and compared them to blood levels of 25-hydroxyvitamin D in 92 age- and sex-matched control subjects with no history of musculoskeletal pain. Both patients and controls were interviewed to obtain demographic information, as well as to assess comorbidities, occupational exposures, personal characteristics, and medications that could interfere with 25-hydroxyvitamin D levels. In addition, solar exposure was also taken into consideration, and patients were asked about their average time spent in the sun and use of sunscreen. Dietary vitamin D intake was also taken into consideration and assed by means of tailored food frequency questionnaires. Depression and pain intensity were assessed using validated interview and assessment tools, and a tender point examination was performed for each participant. The study found no statistically significant differences in the blood levels of 25-hydroxyvitamin D levels of fibromyalgia patients compared to healthy controls. In addition, no differences were detected with regard to the classification of these levels as deficient, insufficient, or sufficient. Furthermore, no correlation was found between 25-hydroxyvitamin D levels and pain intensity (Pena et al., 2010).