Ultraviolet light

About: Ultraviolet light is a research topic. Over the lifetime, 49494 publications have been published within this topic receiving 843151 citations.

Association of Low Vitamin D Levels With the Frailty Syndrome in Men and Women

Abstract: FRAILTY has been described as “a biologic syndrome of decreased reserve and resistance to stressors, resulting from cumulative declines across multiple physiologic systems and causing vulnerability to adverse outcomes” (1) The syndrome is associated with incident falls, functional limitation, disability, and mortality (1,2); thus, preventing frailty may help slow progression of the disablement process in older persons Low 25-hydroxyvitamin D [25(OH)D] levels are common in older adults (3,4) and have been linked to falls (5,6), fractures (5), pain (3,5,7), sarcopenia (4), poor physical function (8,9), disability (3), and frailty (10) Further, vitamin D supplementation has been shown to improve physical function (11,12) The importance of vitamin D in maintaining calcium homeostasis is well known Cholecalciferol is synthesized in the skin in response to ultraviolet light or is ingested through food (eg, fatty fish, eggs, fortified dairy products) and hydroxylated into 25(OH)D in the liver Older persons often have low 25(OH)D levels owing to age-related decreased efficiency of hydroxylation and reduced sunlight exposure (3,13) When 25(OH)D levels are low, active metabolite 1,25-dihydroxyvitamin D [1,25-(OH)2D] and calcium absorption decrease The reduced serum calcium causes parathyroid hormone (PTH) levels to rise to stimulate 1,25-(OH)2D production, resulting in increased bone turnover and hip fracture risk (3,13) Emerging research suggests that vitamin D affects muscle strength and function (4,8), both directly and indirectly through PTH regulation and inflammation (3,4,9,14,15) Many sequelae of low 25(OH)D (3,4,8–10) are considered dimensions of the frailty syndrome (1,2); thus, low 25(OH)D may be a reversible cause of frailty Also, low vitamin D may affect men and women differently Age-related levels of 25(OH)D decline earlier and faster in women than in men (16), which may explain the greater prevalence of frailty in women versus men Whether the pathway to frailty differs by sex is unknown In this study, we examined sex-specific associations between low 25(OH)D and prevalent frailty in community-dwelling men and women aged 65 years and older We also explored PTH as a potential mediator in the pathway between low 25(OH)D and frailty

Non-racemic amino acid production by ultraviolet irradiation of achiral interstellar ice analogs with circularly polarized light

Abstract: The delivery of organic matter to the primitive Earth via comets and meteorites has long been hypothesized to be an important source for prebiotic compounds such as amino acids or their chemical precursors that contributed to the development of prebiotic chemistry leading, on Earth, to the emergence of life. Photochemistry of inter/circumstellar ices around protostellar objects is a potential process leading to complex organic species, although difficult to establish from limited infrared observations only. Here we report the first abiotic cosmic ice simulation experiments that produce species with enantiomeric excesses (e.e.'s). Circularly polarized ultraviolet light (UV-CPL) from a synchrotron source induces asymmetric photochemistry on initially achiral inter/circumstellar ice analogs. Enantioselective multidimensional gas chromatography measurements show significant e.e.'s of up to 1.34% for (13C)-alanine, for which the signs and absolute values are related to the helicity and number of CPL photons per deposited molecule. This result, directly comparable with some L excesses measured in meteorites, supports a scenario in which exogenous delivery of organics displaying a slight L excess, produced in an extraterrestrial environment by an asymmetric astrophysical process, is at the origin of biomolecular asymmetry on Earth. As a consequence, a fraction of the meteoritic organic material consisting of non-racemic compounds may well have been formed outside the solar system. Finally, following this hypothesis, we support the idea that the protosolar nebula has indeed been formed in a region of massive star formation, regions where UV-CPL of the same helicity is actually observed over large spatial areas.

Effects of Nanoanatase TiO2 on photosynthesis of spinach chloroplasts under different light illumination.

Abstract: With a photocatalyzed characteristic, nanoanatase TiO2 under light could cause an oxidation-reduction reaction. Our studies had proved that nano-TiO2 could promote photosynthesis and greatly improve spinach growth. However, the mechanism of nano-TiO2 on promoting conversion from light energy to electron energy and from electron energy to active chemistry energy remains largely unclear. In this study, we report that the electron transfer, oxygen evolution, and photophosphorylation of chloroplast (Chl) from nanoanatase-TiO2-treated spinach were greatly increased under visible light and ultraviolet light illumination. It was demonstrated that nanoanatase TiO2 could greatly improve whole chain electron transport, photoreduction activity of photosystem II, O2-evolving and photophosphorylation activity of spinach Chl not only under visible light, but also energy-enriched electron from nanoanatase TiO2, which entered Chl under ultraviolet light and was transferred in photosynthetic electron transport chain and made NADP+ be reduced into NADPH, and coupled to photophosphorylation and made electron energy be transformed to ATP. Moreover, nanoanatase h+, which photogenerated electron holes, captured an electron from water, which accelerated water photolysis and O2 evolution.