Studies link Vitamin D deficiency to nonskeletal disorders. To date, deficiency is difficult to assess. UVB therapy might benefit certain individuals.
Vitamin D deficiency is a worldwide epidemic. In the United States, close to 36% of young adults without apparent health conditions and 57% of adult, hospitalized patients are vitamin D deficient, according to Mayo Clinic Proceedings and Nutrition Journal.
In the United Kingdom, an estimated 60% of middle-aged adults suffer from vitamin D deficiency. Recent studies suggest that vitamin D supplementation could benefit medical conditions other than diseases of the bone. Researchers face the problem that measurements of vitamin D levels do not reliably correlate with the risk of deficiency-related medical conditions. In addition, treatment involving the use of an artificial source of ultraviolet B light could potentially benefit certain vitamin D deficient individuals.
Vitamin D, a fat-soluble vitamin, is derived from sun exposure, dietary sources and supplements. Few foods are naturally rich in vitamin D, but certain dairy products, juices and cereals are fortified with vitamin D. The bone diseases classically associated with vitamin D deficiency are rickets in children and osteomalacia in adults.
Exposure to ultraviolet B light from the sun results in the formation of vitamin D in the skin. Vitamin D is transported in the bloodstream to the liver, where it is converted to 25-hydroxyvitamin D or 25(OH)D. Measurement of serum 25(OH)D levels is used to assess vitamin D deficiency. Besides individuals with insufficient intake of vitamin D, those with certain medical conditions, such as Crohn’s disease, which is associated with impaired intestinal absorption of vitamin D, are at risk of Vitamin D deficiency.
Strong evidence generated by randomized clinical trials links vitamin D supplementation to a reduced risk of falls and bone fractures in the elderly, as reported in Mayo Clinic Proceedings and Nutrition Journal. Only doses of vitamin D above 400IU per day decreased the risk of fractures, while doses of 700IU or higher per day were needed to decrease the risk of falls.
To date, numerous studies suggest that vitamin D supplementation can reduce the risk of a multitude of nonskeletal medical conditions, including heart disease, diabetes, cancer, multiple sclerosis, asthma, infection, mental illnesses, myalgias, and renal disease. However, most of these studies are observational, and considered unconvincing because they are not based on the gold standard of a randomized clinical trial.
The term “vitamin D deficiency,” defined as 25(OH)D serum levels below 10ng/ml, is associated with bone disease, while the term “insufficiency,” defined as 25(OH)D levels of 11 to 20ng/ml, applies to nonskeletal disorders, according to Mayo Clinic Proceedings. However, these definitions are controversial, since significant numbers of individuals classified as “deficient,” or “insufficient,” based on measured 25(OH)D levels, do not have symptoms or signs of deficiency. Furthermore, studies showed that the same dose of vitamn D, or an equivalent exposure to sunlight, resulted in highly variable 25(OH)D levels, ranging from 11 to as high as 71ng/ml in one sun exposure study. The health outcome in relation to a measured level of 25(OH)D likely depends on multiple factors, including calcium intake, age, physical activity and fat stores, as well as individual genetic variation.
A recent review in Nutrition Journal proposes the use of an artificial source of ultraviolet B (UVB) light in the treatment of Vitamin D deficiency. Unlike vitamin D supplementation, UVB light does not carry the risk of vitamin D toxicity. However, optimal duration of exposure varies between individuals and must be established to prevent erythema (redness of the skin resulting from injury to small blood vessels). In addition, a device that generates the optimal wavelength of UVB light must be used. UVB irradiation is not suitable for individuals taking certain medications, such as insulin, or those with medical conditions, such as pulmonary tuberculosis or dermatitis.