Vitamina D / Vitamin D

O termo vitamina D engloba um grupo de moléculas secosteroides derivadas do 7- deidrocolesterol (7-DHC ou provitamina D) interligadas através de uma cascata de reações fotolíticas e enzimáticas que acontecem em células de diferentes tecidos. (CASTRO, 2011). Nos seres humanos, apenas 10% a 20% da vitamina D necessária à adequada função do organismo provém da dieta. (CASTRO, 2011). O restante, cerca de 80%, da vitamina D é produzida na pele após a exposição à radiação ultravioleta B ­ UVB (HOLICK, 2008)

The term vitamin D encompasses a group of secosteroid molecules derived from 7- dehydrocholesterol (7-DHC or provitamin D) interconnected through a cascade of photolytic and enzymatic reactions that occur in cells of different tissues. (CASTRO, 2011). In humans, only 10% to 20% of the vitamin D needed for proper body function comes from the diet. (CASTRO, 2011). The remainder, about 80%, of vitamin D is produced in the skin after exposure to ultraviolet radiation B ­ UVB (HOLICK, 2008)

Importancia de la Vitamina D en la época del COVID-19 / Importance of Vitamin D in the time of COVID-19

"Los coronavirus pertenecen a una gran familia de virus (Coronaviridae) que infectan aves y varios mamíferos. El coronavirus actualmente denominado SARS-CoV-2, fue descubierto en diciembre de 2019 en Wuhan, provincia de Hubei, China, y es el agente causal de la epidemia de neumonía atípica actual" (COVID-19; Coronavirus Disease 2019). Los casos más graves presentan un síndrome de dificultad respiratoria aguda que puede conducir a la muerte. La vitamina D (VD), además del efecto bien conocido y positivo sobre la salud ósea y la homeostasis del calcio, tiene efecto pleiotrópico en varios órganos, con distribución casi universal del receptor de VD y de las enzimas de metabolización de 25 hidroxivitamina D (25OHD) en las células del organismo. Estas acciones extraesqueléticas dependen de la síntesis en dichas células del metabolito activo 1,25 dihidroxivitamina D por regulación paracrina y autocrina, dependiente de niveles circulantes óptimos de 25OHD. Por sus acciones inmunomoduladora, antiinflamatoria, antimicrobiana, reguladora del sistema renina-angiotensina-aldosterona, favorecedora de la indemnidad del epitelio respiratorio y la homeostasis redox celular, la VD podría tener efecto protector en la infección por COVID-19. Entre los grupos de riesgo para COVID-19 figuran los adultos mayores, obesos, diabéticos, hipertensos, con afecciones cardiovasculares, patologías con mayor incidencia en individuos con hipovitaminosis VD. La suplementación con VD, para alcanzar niveles óptimos de 25OHD de 40-60 ng/ml, podría reducir la incidencia, severidad y riesgo de muerte en la actual pandemia por COVID-19, como medida complementaria mientras se desarrollan la vacuna y otras medicaciones específicas. (AU)

Coronaviruses belong to a large family of viruses (Coronaviridae) that infect birds and various mammals. The novel coronavirus currently known as SARS-CoV-2 was discovered in December 2019 in Wuhan, Hubei province, China and is the causal agent of the current atypical pneumonia epidemic (COVID-19: Coronavirus Disease 2019); The most severe cases present with acute respiratory distress syndrome that can lead to death. Vitamin D (VD) has a pleiotropic effect on several organs, in addition to its wellknown and positive effect on bone health and calcium homeostasis, with an almost universal distribution of the VD receptor and the metabolites of 25hydroxyvitamin D (25OHD) in all cells of the body. These extra-skeletal actions depend on the synthesis of the active metabolite 1,25dihydroxyvitamin D in the cells depending on the optimal circulating levels of 25OHD and though paracrine and autocrine regulation. Due to its immunomodulatory, anti-inflammatory, antimicrobial, and regulatory actions on the renin angiotensin aldosterone system, which favors the compensation of the respiratory epithelium and cellular redox homeostasis, the VD could have a protective effect on COVID-19 infection. Among the risk groups for COVID-19 are obese, diabetic, and hypertensive patients, subjects with cardiovascular conditions, and elderly people. All these pathologies show a higher incidence in individuals with VD hypovitaminosis. VD supplementation, to achieve optimal 25OHD levels of 40-60 ng/ml, could reduce the incidence, severity, and risk of death in the current COVID-19 pandemic, as a complementary measure while the vaccine and other specific therapies are being developed. (AU)

Sun exposure, skin lesions and vitamin D production: evaluation in a population of fishermen

Abstract: Background: Exposure to UVR provides benefits related to vitamin D synthesis, but also causes harms, since UVB is considered a complete carcinogen. There is no definition of the level of sun exposure and the proportion of exposed body required for proper synthesis of vitamin D in the skin without causing it damage. Objectives: This study aims to analyze the sun exposure index, vitamin D levels and clinical changes in the skin caused by constant sun exposure in the fishermen population. Methods: It is a cross-sectional, observational and analytical study. The sample consisted of fishermen and was calculated in 174 individuals. The questionnaire was applied, the dermatological examination was carried out and the examinations of calcidiol, parathyroid hormone, calcium and phosphorus were requested. Data were expressed as percentages. The comparative analysis was done through the Chi-square test, and the correlations were established through the Pearson's linear coefficient. Results: We observed that there was vitamin D deficiency in a small part of the cases (11.46%), and the frequency of diagnosis of skin cancer was 2.7% of the cases surveyed. Study Limitations: The difficulty in categorizing the sun exposure index. Conclusion: The fact that fishermen expose themselves to the sun chronically and have been exposed to the sun for more than 15 years, between 21 and 28 hours a week, and without photoprotection, were indicative factors for protection against vitamin D deficiency. Chronic exposure to sun and high vitamin levels D may be indicative of protection of this population against skin cancer.

On the synthesis of vitamin d in the darkness / Sobre la síntesis de vitamina D en la oscuridad

Published evidence reports the existence of two routes for the transformation of 7-dehydrocholecalciferol into previtamin D3: a photochemical route with the participation of UVB photons and another route that occurs in the darkness. Several reports appears to support the presence of these two routes in some mammals, birds, nonvascular plants (e.g.: mosses), vascular plants (e.g.: angiosperms) and lichens. The reviewed evidence suggests that in the darkness, the synthesis of vitamin D3 follows the same scheme of the photochemical pathway, but at a reduced rate respect to the synthesis under UVB radiation. The process of vitamin D synthesis in the dark, then, may be taken as an insurance for survival, at least for mammals and birds. The low rate of the synthesis of vitamin D3 in the absence of light produce low concentrations of vitamin D3 metabolites in plasma. Long term survival under these circumstances might be possible through upregulation of vitamin D receptors (VDRs). In mole rats (South African rodents that live in the dark in underground tunnels), the reduced rate of vitamin D3 synthesis produce low levels of plasma vitamin D3 and their metabolites 25(OH) D3 and 1α,25OH2 D3 . The fact that Kd and ßmax of the complex 1α,25(OH)2 D3 -VDR from the intestinal mucosa, kidneys and the Harderian glands of the mole rat Heterocephalus glaber are significantly different in each one of these tissues, is interpreted as an indicator that the VDRs are, in each tissue, adapted to the maintenance of normal physiological functions. (AU)

Varios trabajos publicados han informado que existen dos mecanismos para la transformación de 7-dehidrocolecalciferol en previtamina D3 : uno iniciado con el auxilio de fotones UVB y un segundo que ocurre en la oscuridad, sin el auxilio de radiación ultravioleta. Una serie de publicaciones contienen información que apoya la presencia de estos dos mecanismos en mamíferos, pájaros, plantas no vasculares (musgos), vasculares (angiospermas) y líquenes. La evidencia revisada sugiere que, en la oscuridad, la síntesis de vitamina D3 sigue el mismo esquema que la ruta fotoquímica y generalmente ocurre a una tasa reducida respecto de la síntesis bajo irradiación ultravioleta. La operación de la síntesis de vitamina D3 en la oscuridad, por lo menos para mamíferos y pájaros, puede tomarse como un reaseguro de sobrevida. La reducida tasa de síntesis de vitamina D en ausencia de luz produce bajas concentraciones en plasma de los metabolitos de la vitamina. La sobrevida saludable en estas condiciones sería posible mediante upregulation de los receptores. En las ratas topo Heterocephalus glaber (roedores sudafricanos que viven en permanente oscuridad, en túneles subterráneos), la reducida tasa de síntesis de vitamina D3 es la causa de los bajos niveles plasmáticos de la vitamina y sus metabolitos: 25(OH)D3 y 1α,25OH2 D3 . El hecho de que el Kd y ßmax del complejo 1α,25(OH)2 D3 -Vitamina-D-Receptor del intestino, riñón y glándulas de Harder de Heterocephalus glaber sean significativamente diferentes entre sí indicaría que los receptores se han modificado para mantener funciones fisiológicas normales en cada tejido. (AU)

Hipovitaminosis D: afectaciones no clásicas / Hypovitaminosis D: non-classical effects

El déficit de vitamina D es una situación prevalente a nivel mundial y afecta a personas de cualquier edad. El rol más importante de la vitamina D es la regulación de la absorción intestinal de calcio y el metabolismo de calcio y fósforo para mantener la homeostasis ósea y muscular. Las enfermedades clásicamente asociadas al déficit de esta hormona son el raquitismo en los niños. En los adultos, el espectro varía desde osteomalacia hasta hiperparatiroidismo secundario, con pérdida de masa ósea, aumento del riesgo de caídas e incremento del riesgo de fractura según el grado de deficiencia. Además de estas acciones clásicas, la vitamina D: regula el crecimiento y la diferenciación de células musculares lisas de los vasos sanguíneos, el sistema renina-angiotensina-aldosterona, favorece la liberación de insulina, regula el crecimiento y estimula la diferenciación de monocitos-macrófagos, células presentadoras de antígenos, células dendríticas y linfocitos. En los últimos años, numerosos autores han vinculado a la hipovitaminosis D con enfermedades autoinmunes, diabetes mellitus tipo 2, enfermedades cardiovasculares, cáncer, etc. Estas afecciones no asociadas clásicamente al déficit de vitamina D serán el objeto de esta revisión.

Vitamin D deficiency is prevalent worlwide and affects people of all ages. Calcium intestinal absorption regulation along with calcium, phosphorous and bone homeostasis are most important vitamin D roles. Raquitism is commonly associated with vitamin D deficiency in children. Vitamin D deficiency related diseases varies from osteomalacia to hyperparathyroidism (with bone loss and increased risks of falls and fractures) in adults. Besides this well known actions, vitamin D regulates the growth and differentiation of smooth muscle cells, regulates the renin-angiotensin-aldosterone system, promotes the release of insulin, regulates cell growth and stimulates the differentiation of monocytes-macrophages, antigen presenting cells, dendritic cells and lymphocytes. In recent years, many authors have linked to hypovitaminosis D with autoimmune diseases, Type2 diabetes mellitus, cardiovascular disease and cancer among others diseases. These not traditionally vitamin D deficiency associated conditions are going to be subjects for this review.

Serum levels of 25-old in infants: Impact of sun exposure and diet

Serum levels of 25-hydroxy-vitamin D [25-OHD], calcium [Ca], phosphorus [P] and albumin were measured cross-sectionally in 3 seasons in infants aged 6 - 22 months: 37 infants were studied in late summer [July and August], 36 infants were studied in early winter [November and December] and 57 infants were studied in spring [March and April] in a village nearby Cairo. All infants came from low socioeconomic background. The aim of this work is to study the relative influence of sunlight exposure, dietary intake and age on serum levels of 25-OHD, calcium and phosphorus serum levels. 25- OHD mean levels showed significant difference between the 3 seasons being highest in summer [31.7 +/- 20 ng/ml] vs. 18.1 +/- 14 ng/ml and 14.8 +/- 9 ng/ml in winter and spring, respectively. Serum calcium did not show significant difference, while serum phosphorus was highest in spring and serum albumin was highest in summer. None of the nutritional elements intake correlated with serum 25-OHD Ca, P or albumin. Age positively correlated with 25-OHD serum levels, but not Ca, P and albumin. Infants above one-year old showed 25-OHD mean level significantly higher than in infants under one year of age