Is vitamin D the fountain of youth?

Calcium and vitamin D in human health: Hype or real?

The incidence and prevalence of vitamin D deficiency are increasing worldwide. It is estimated that over 50% of the world's population have low vitamin D (i.e., hypovitaminosis D; serum levels below 30 ng/mL). In vitamin D inadequacy, human physiological systems work inefficiently. In humans, 80% of the vitamin D is synthesized in the presence of ultraviolet rays from sunlight; for the rest, we rely on diet and nowadays, supplements. The latter becomes important when one is exposed to less than optimal amounts of sunlight, inability to generate vitamin D in the skin efficiently, and/or having conditions that lead to decreased intestinal absorption or increased catabolism of vitamin D. The normal serum 25-hydroxyvitamin D [25(OH)D] level is around 30 ng/mL (75 nmol/L) and the optimal range is between 30 and 60 ng/mL (75-150 nmol/L). In 2011, the Institute of Medicine (IOM) suggested that 600IU of vitamin D is adequate for people below age 71 who are not exposed to sunshine. Although this might be relevant to the ambulatory healthy white Caucasians to achieve serum 25(OH)D level of 20 ng/mL, but it is insufficient for other ethnic groups. Moreover, the IOM recommendations are not suitable for those who live outside North America. Vitamin D requirements are higher during adolescence, pregnancy and lactation, and in many other disease conditions. Most clinicians consider 30 ng/mL as the minimum serum level of 25(OH)D necessary to maintain good health. In the absence of sunlight exposure and with daily oral intake of 600IU vitamin D, very few people would reach serum 25(OH)D level above 30 ng/mL. While an additional daily intake of 1000IU of vitamin D are required for people with lighter-skin color, those with darker complexion and the elderly, require a minimum of 2000IU/day to maintain serum 25(OH)D levels over 30 ng/mL; 5000 IU/day supplement is considered as the safe daily upper limit of supplementation. Vulnerable groups such as the disabled and/or house-bound, obese, with gastrointestinal abnormalities and/or malabsorption syndromes, institutionalized people (e.g., nursing homes, prisons, etc.), and pregnant and lactating women need approximately 4000IU per day for optimal physiological activity. Vitamin D is essential for gastrointestinal calcium absorption, mineralization of osteoid tissue and maintenance of serum ionized calcium level. It is also important for other physiological functions, such as muscle strength, neuromuscular coordination, hormone release, subduing autoimmunity, and curtailing the development of certain cancers.

Non-musculoskeletal benefits of vitamin D

The aim of this study is to determine and critically evaluate the plausible relationships of vitamin D with extra-skeletal tissues in humans. Severe vitamin D deficiency results in rickets in children and osteomalacia in adults; these beneficial effects in the musculoskeletal system and certain physiological functions are well understood. Nevertheless, mounting reports support additional beneficial effects of vitamin D, outside the musculoskeletal system. This review explores the recent advances in knowledge about the non-skeletal effects of vitamin D. Peer-reviewed papers were extracted from research databases using key words, to assess correlations between vitamin D and extra-skeletal diseases and conditions. As per the guidelines of the Preferred Reporting Items for Systematic Reviews (PRISMA); general interpretations of results are included; taking into consideration the broader evidence and implications. This review summarizes current knowledge of the effects of vitamin D status on extra-skeletal tissues with special attention given to relationships between vitamin D status and various diseases commonly affecting adults; the effects of intervention with vitamin D and exposure to sunlight. Evidence suggests that vitamin D facilitates the regulation of blood pressure; and cardiac; endothelial; and smooth muscle cell functions; playing an important role in cardiovascular protection. In addition; 1,25(OH)₂D improves immunity; subdues inflammation; and reduces the incidence and severity of common cancers; autoimmune diseases and infectious diseases. Almost all adequately powered; epidemiological and biological studies that use; adequate doses of vitamin D supplementation in D-deficient populations have reported favorable outcomes. These studies have concluded that optimizing 25(OH)D status improves the functionality of bodily systems; reduces comorbidities; improves the quality of life; and increases survival. Although accumulating evidence supports biological associations of vitamin D sufficiency with improved physical and mental functions; no definitive evidence exists from well-designed; statistically powered; randomized controlled clinical trials. Nevertheless, most studies point to significant protective effects of vitamin D in humans when the minimum 25(OH)D serum level exceeds 30ng/mL and is maintained throughout the year.

Vitamin D deficiency and its role in muscle-bone interactions in the elderly

In this commentary, we focus on common 'downstream' links of vitamin D between muscle and bone health. Both direct and indirect effects of 1,25 dihydroxyvitamin D (1,25(OH)D) link the mutual age-related decline in muscle function and bone density, independent of physical activity. Changes in calcium absorption associated with vitamin D deficiency affect both muscle and bone mass. The age-related decline in vitamin D receptor expression and 1,25(OH)D activity impact on proinflammatory cytokines such as tumor necrosis factor -α and interleukin-6 in skeletal muscle and vitamin D deficiency appears to enhance both bone marrow adipogenesis and intramuscular adipose tissue impacting as reduced functionality in both skeletal tissues. Controversial findings on the role of 1,25(OH)D on skeletal muscle may relate to differences in vitamin D receptor expression throughout different stages of muscle cell differentiation. Prolonged vitamin D insufficiency in the elderly is associated with reductions in both bone mineral density and type 2 muscle fibers with the outcomes of skeletal fragility in combination with reduced muscle power, leading to increased risk of falls and fracture.

Vitamin D insufficiency and chronic diseases: hype and reality

In recent years an increasing number of observational studies have suggested that a low vitamin D status contributes to the development of all sorts of chronic diseases. In reality, however, studies that had been adequately controlled for confounding factors ruled out any link between vitamin D insufficiency and, for example, metabolic disorders, arterial hypertension, multiple sclerosis or cognitive dysfunction. Furthermore, a role of vitamin D insufficiency in autoimmune diseases is evident only in animal models but has not yet been established in humans. In respect to many malignancies, vitamin D insufficiency is only one out of many risk factors and its specific impact on disease incidence has never been assessed. There is convincing evidence, however, that vitamin D insufficiency is a major risk factor for osteoporosis, colorectal and breast cancer as well as for cardiovascular disease and mortality. However, it is debatable that circulating 25-hydroxyvitamin D concentrations of 100-150 nmol l(-1) are required for optimal health outcomes. These are overestimates which would afford to raise vitamin D intake to 4000 IU day(-1). In reality, high doses of vitamin D can cause serious health problems because of the U-shaped dose-response relationships that exist in some cases. Data from large cohort studies clearly indicate that serum 25-(OH)D concentrations around 50 nmol l(-1) are sufficient to minimize the risk of osteoporotic fractures, colorectal and breast cancer, and cardiovascular mortality. The fact that the risk-reducing potential of vitamin D depends on adequate calcium nutrition is widely ignored. I here summarize the evidence that efficient disease prevention does not require intake of more vitamin D and calcium than currently recommended for maintaining optimal bone health.

Vitamin D in the new millennium

The incidence of vitamin D deficiency is rising worldwide, yet in the vast majority of patients, the condition remains undiagnosed and untreated. Current evidence overwhelmingly indicates that supplemental doses greater than 800 IU/day have beneficial effects on the musculoskeletal system, improving skeletal homeostasis, thus leading to fewer falls and fractures. Evidence is also accumulating on the beneficial effects of vitamin D on extraskeletal systems, such as improving immune health, autoimmune disorders, cancer, neuromodulation, diabetes, and metabolic syndrome. The cause-effect relationship of vitamin D deficiency with increasing incidences of nonskeletal disorders is being investigated. Published reports support the definition of sufficiency, serum levels of 25-hydroxyvitamin D [25(OH)D] greater than 30 ng/mL (75 nmol/L). To achieve this, most people need vitamin D supplementation ranging from 600 to 2000 IU/day; consumption up to of 5000 international units (IU) per day of vitamin D is reported as safe. Although light-skinned individuals need 1000 IU/day of vitamin D, elderly and dark-skinned individuals are likely to need approximately 2000 IU/day to maintain serum 25(OH)D levels greater than 30 ng/mL. Other vulnerable patients, such as the obese, those who have undergone bariatric surgery, and those with gastrointestinal malabsorption syndromes, may require higher doses of vitamin D to maintain normal serum levels and be healthy.

Advances in the understanding of mineral and bone metabolism in inflammatory bowel diseases

Chronic inflammatory disorders such as inflammatory bowel diseases (IBDs) affect bone metabolism and are frequently associated with the presence of osteopenia, osteoporosis, and increased risk of fractures. Although several mechanisms may contribute to skeletal abnormalities in IBD patients, inflammation and inflammatory mediators such as TNF, IL-1β, and IL-6 may be the most critical. It is not clear whether the changes in bone metabolism leading to decreased mineral density are the result of decreased bone formation, increased bone resorption, or both, with varying results reported in experimental models of IBD and in pediatric and adult IBD patients. New data, including our own, challenge the conventional views, and contributes to the unraveling of an increasingly complex network of interactions leading to the inflammation-associated bone loss. Since nutritional interventions (dietary calcium and vitamin D supplementation) are of limited efficacy in IBD patients, understanding the pathophysiology of osteopenia and osteoporosis in Crohn's disease and ulcerative colitis is critical for the correct choice of available treatments or the development of new targeted therapies. In this review, we discuss current concepts explaining the effects of inflammation, inflammatory mediators and their signaling effectors on calcium and phosphate homeostasis, osteoblast and osteoclast function, and the potential limitations of vitamin D used as an immunomodulator and anabolic hormone in IBD.

Updates on osteonecrosis of the jaw

PURPOSE OF REVIEW

Osteonecrosis of the jaw (ONJ) is an uncommon condition noted to occur in patients with cancer who are receiving intravenous bisphosphonates. The cause of ONJ remains unknown. The leading hypotheses addressing the mechanism of ONJ are reviewed here.

RECENT FINDINGS

The present clinical data suggest that ONJ may occur in approximately 5% of patients with metastatic bone disease. The ability to predict an individual's risk of developing ONJ remains elusive. It is likely that an altered bone microenvironment and/or host defense mechanisms effected by medications used to treat patients with metastatic bone disease contributes to the development of ONJ. Medications that significantly reduce osteoclastic activity are associated with ONJ. Preclinical models of ONJ are being developed but to establish such an intricate systemic condition in animals is challenging.

SUMMARY

The ONJ field has progressed via knowledge gained by case reports, population-based studies, and emerging animal models. Still, there are myths that need to be resolved and important clues that need to be investigated. Understanding the pathophysiology of this condition will be critical to improve patient care. Communications between oncologists, dentists, basic scientists, and patients are central to effective treatment and research for this condition.

Is hypovitaminosis D one of the environmental risk factors for multiple sclerosis?

The role of hypovitaminosis D as a possible risk factor for multiple sclerosis is reviewed. First, it is emphasized that hypovitaminosis D could be only one of the risk factors for multiple sclerosis and that numerous other environmental and genetic risk factors appear to interact and combine to trigger the disease. Secondly, the classical physiological notions about vitamin D have recently been challenged and the main new findings are summarized. This vitamin could have an important immunological role involving a number of organs and pathologies, including autoimmune diseases and multiple sclerosis. Furthermore, human requirements for this vitamin are much higher than previously thought, and in medium- or high-latitude countries, they might not be met in the majority of the general population due to a lack of sunshine and an increasingly urbanized lifestyle. Thereafter, the different types of studies that have helped to implicate hypovitaminosis D as a risk factor for multiple sclerosis are reviewed. In experimental autoimmune encephalomyelitis, vitamin D has been shown to play a significant immunological role. Diverse epidemiological studies suggest that a direct chain of causality exists in the general population between latitude, exposure to the sun, vitamin D status and the risk of multiple sclerosis. New epidemiological analyses from France support the existence of this chain of links. Recently reported immunological findings in patients with multiple sclerosis have consistently shown that vitamin D significantly influences regulatory T lymphocyte cells, whose role is well known in the pathogenesis of the disease. Lastly, in a number of studies on serum levels of vitamin D in multiple sclerosis, an insufficiency was observed in the great majority of patients, including at the earliest stages of the disease. The questionable specificity and significance of such results is detailed here. Based on a final global analysis of the cumulative significance of these different types of findings, it would appear likely that hypovitaminosis D is one of the risk factors for multiple sclerosis.