Valuable verities on vitamin D

Normal bone metabolism clearly requires vitamin D, it is undisputed for its classic role in bone metabolism, calcium and phosphorus homeostasis. Recently, a worldwide focus has been directed on the extra-skeletal effects of this vitamin. The New York Times even called it the “wonder drug”. Vitamin D is obtained by synthesis in the skin after ultraviolet B exposure or through food consumption. A shortage of vitamin D may cause osteomalacia, with muscle weakness and fatigue in children (rickets) as well as in adults. It is often an underestimated problem, especially in people with dark skin and in those lacking sun exposure. It is one of the causes of osteoporosis. But vitamin D plays a role in many other disorders. Studies have shown associations between low 25hydroxyvitamin D (25-[OH]D) levels and risk for fractures, falls, cardiovascular disease, colorectal cancer, diabetes, depressed mood, cognitive decline and even death. The potential extra-skeletal wonderful effects of vitamin D have revived further interest into particularly cardiovascular effects, antitumor properties, and last but not least, effects on the immune system. In many rheumatic diseases a low level of vitamin D appears to be associated with disease severity, including systemic lupus erythematosus, fibromyalgia syndrome, especially in those with anxiety and depression, but also in osteoarthritis, rheumatoid arthritis (RA) and systemic sclerosis. Vitamin D deficiency is determined by measuring total serum 25-(OH)D concentrations. Measuring 25(OH)D levels is complicated by the presence of multiple assays, evidence of inter-method and inter-laboratory variability in measurement and the lack of an internationally recognized, commutable vitamin D reference standard. Efforts to increase standardization are in progress. There is also no consensus on optimal 25-(OH)D concentrations. Although experts generally agree that levels lower than 50 nmol/L (20 ng/mL) are associated with worse bone health, disagreement exists about the optimal 25-(OH)D levels and exact thresholds. According to NHANES (National Health and Nutrition Examination Survey) data from 2001 to 2006, 33% of the US population was at risk for 25-(OH)D levels below 50 nmol/L (20 ng/mL) and 77% had 25-(OH)D levels below 75 nmol/L (30 ng/mL). Risk factors for low vitamin D levels include: darker skin pigmentation, low vitamin D intake, little or no ultraviolet B exposure and obesity. Older age, female sex, low physical activity, low education attainment and low health status were factors also associated with vitamin D deficiency in some studies.