Vitamin D - A Novel Therapy for Chronic Diseases? E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Ratgeber
- Sprache: Englisch
Vitamin D – A Novel Therapy for Chronic Diseases? This comprehensive book explores the vital role of vitamin D in human health, with a focus on its potential impact on various chronic diseases. Starting with the history and general information of vitamin D, the book covers various topics, including its effects on immunity, gut health, insulin resistance, cardiovascular disease, irritable bowel syndrome, depression, melanoma, and pregnancy. It provides clear and evidence-based insights into how vitamin D influences the body and its role in preventing or managing specific conditions.
This book is a valuable resource for dietitians, healthcare professionals, and anyone seeking to enhance their understanding of vitamin D and its therapeutic potential.
Key Features:
- Covers the role of vitamin D in chronic diseases
- Explores vitamin D’s impact on immunity, gut health, and insulin resistance
- Provides evidence-based recommendations for healthcare professionals
- Accessible explanations for non-expert readers
Readership: Dietitians, doctors, nurses, healthcare professionals, and general readers interested in health and wellness.
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Seitenzahl: 250
Veröffentlichungsjahr: 2024
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FOREWORD
In today's swiftly evolving world, where information is abundant and choices are vast, the quest for nutritional wisdom can seem overwhelming. Amid the myriad of dietary trends and the maze of conflicting advice, certain essentials of nutrition emerge as pillars of human health. Prominent among these is vitamin D, a nutrient that has captured the fascination of scientists and the public alike for its critical role in our well-being.
It is my distinct pleasure to present to you a comprehensive exploration of one of the most pivotal vitamins for human health: vitamin D. This book invites you on a journey through the complex world of this remarkable nutrient, shedding light on its crucial functions in the body, its varied sources, and its profound influence on health, with a particular focus on its impact on certain diseases.
The relationship between vitamin D and bone health is widely recognized, yet the scope of its benefits stretches far beyond its role in calcium metabolism. Vitamin D is instrumental in supporting immune function, enhancing mood, and potentially lowering the risk of chronic diseases, captivating researchers, and health professionals with its multifaceted effects. The evolving narrative of vitamin D is one versatility and discovery, with each chapter of research enriching our understanding of its significance.
This book is designed not only as a collection of the latest knowledge but also as a practical guide for those aiming to improve their vitamin D levels. Through clear, evidence-based recommendations and accessible explanations, it equips readers with the tools to make informed health decisions. Whether you are a healthcare professional, a nutrition aficionado, or simply someone interested in the pivotal role of nutrition in health, this book provides valuable insights that can have a lasting impact on your life.
As we venture into the following chapters, let us seize the opportunity to deepen our appreciation for vitamin D, exploring its potential to bolster our health and vitality. May this book illuminate your path to optimal health, serving as a beacon in your pursuit of well-being.
With warm regards
PREFACE
The health of the musculoskeletal system depends on vitamin D since it controls the metabolism of calcium and phosphorus. For most people, sunlight with enough ultraviolet B (UVB) radiation is the primary source of it, as it is synthesized in the skin upon exposure. Foods and dietary supplements can also provide it. When exposure to sunlight containing UVB radiation is restricted or limited (as in the winter months), dietary sources become crucial (e.g., due to lack of time spent outdoors or little skin exposure).
Vitamin D is acquired by humans through their food and exposure to sunshine. Vitamin D is found naturally in very few foods. Vitamin D3 is abundant in oily fish, including sardines, salmon, and mackerel. Vitamin D is said to be present in egg yolks, yet the concentrations are somewhat varied. Moreover, egg yolks are a poor source of vitamin D due to their high cholesterol content. Additionally, a few foods—like milk, orange juice, and some bread and cereals—are fortified with vitamin D.
In two hydroxylation steps, vitamin D is transformed into its active metabolite, 1,25-dihydroxyvitamin D (1,25(OH)2D). The primary circulating metabolite of vitamin D, 25(OH)D, is produced in the liver during the first hydroxylation of vitamin D. It is frequently utilized as a biomarker of vitamin D status. In the kidney, 25(OH)D is converted into 1,25(OH)2D during the second hydroxylation. A deficiency of vitamin D is characterized by most specialists as a level of under 20 ng for each milliliter. In 1997, the Institute of Medicine of the US National Academy of Sciences recommended new adequate intakes for vitamin D as 200 IU for children and adults up to 50 years of age, 400 IU for adults 51 to 70 years of age, and 600 IU for adults 71 years of age or older. Vitamin D deficiency can be divided based on UBV, dark skin, being old, and latitude, season, and time of the day of UBV. The other category includes medical/physical conditions or any deficiency, such as fat malabsorption, obesity, chronic kidney disease, and use of medication (e.g. anticonvulsant).
The chapters below discuss the most updated research data available on Vitamin D and its relation to several chronic diseases.
List of Contributors
History and General Information of Vitamin D
Amina Afrin1,*,Anam Shakil Kalsekar1,Khawla Jalal1,Rahab Sohail1,Sharfa Khaleel1,Shaima T. Saleh1,Dimitrios Papandreou1Abstract
The historical background of vitamin D for well-being dates to the beginning of the twentieth century. There are two types of vitamin D; ergocalciferol (D2) and cholecalciferol (D3). While D3 is mostly produced in the skin when exposed to sunshine, vitamin D2 is sourced from plant sources and is frequently utilized in fortified meals and supplements. The recommended form of vitamin D for supplementation is D3 since it has a greater potency in elevating and sustaining blood levels of the nutrient. The biochemistry of vitamin D is centered on how it becomes activated in the kidneys and liver to become its active form, which controls the metabolism of phosphorus and calcium. Although ideal serum levels might vary based on personal health considerations, recommended values generally lie between 20 and 50 ng/mL. Egg yolks, fortified dairy products, and fatty fish are good dietary sources of vitamin D; nevertheless, obtaining a sufficient intake only through food may be difficult, necessitating supplementation. However, overindulgence can result in toxicity, which is defined by hypercalcemia and associated symptoms including nausea and weakness. This emphasizes the significance of moderation in supplementing. Because vitamin D is fat-soluble, the body will keep excess rather than quickly excrete it, therefore taking too many supplements can be harmful. While vitamin D is essential for many body processes, getting the right amount of it without running the risk of negative side effects is crucial.
INTRODUCTION
Vitamin D is indeed a crucial nutrient for human health, playing a significant role in various physiological processes beyond just bone health. The primary natural source of vitamin D is through the synthesis of cholecalciferol (vitamin D3) in the skin upon exposure to UV-B radiation from sunlight. Vitamin D can also be obtained from dietary sources such as fatty fish (e.g., salmon, mackerel, tuna),
fortified foods (e.g., milk, orange juice, cereals), and supplements. Vitamin D plays a crucial role in enhancing the absorption of calcium from the intestines, thereby aiding in maintaining bone health. It regulates calcium and phosphate metabolism, which is essential for bone mineralization and growth. It may also play a role in muscle function and reducing the risk of falls, especially in older adults. Vitamin D also has immunomodulatory effects, influencing both innate and adaptive immune responses. Severe vitamin D deficiency can lead to rickets in children, characterized by skeletal deformities due to impaired mineralization of bones. In adults, severe deficiency can result in osteomalacia, causing weak, soft bones and muscle weakness. Dietary recommendations for vitamin D intake vary by age, sex, and other factors. In the absence of sufficient sunlight exposure, obtaining vitamin D from diet and supplements becomes crucial. While sunlight is a natural source of vitamin D, recommendations regarding sun exposure should balance the benefits of vitamin D synthesis with the risks of skin cancer. Sunscreen use, clothing coverage, time of day, latitude, and skin type all affect the synthesis of vitamin D from sunlight. Overall, maintaining adequate levels of vitamin D is essential for overall health and well-being, and a balanced approach that includes a combination of sunlight exposure, dietary sources, and supplementation when necessary, is recommended.
History of Vitamin D
The story of the discovery of Vitamin D is an interesting one since it was far from a straightforward path. Several lines of research taking place between the 1700s to the 1900s led to its eventual recognition. Since the 1600s, rickets also known as the “English disease”, was rampant in different parts of the world, most notably Europe [1, 2]. This time period was marked by the advent of the Industrial revolution bringing in large amounts of air pollution from the burning of fossil fuels and mills, greatly reducing the amount of sunlight available at the ground level. Furthermore, large populations of people migrated into these crowded, air-polluted areas with little to no sunlight exposure. Concurrent to this large-scale migration, was the spread of a new, bone-softening disorder known as ‘childhood rickets’ when presenting in young children and ‘osteomalacia’ in adults [3]. Daniel Whistler from the Netherlands was first reported to have described rickets and osteomalacia in 1645 as a condition characterised by a poorly mineralized and deformed skeletal system [1]. Around that time, Franklin Glisson documented lithographic records in his book titled De Rachitide in 1650 featuring children with common symptoms such as bowing of the legs, skeletal deformities, growth retardation, enlargement of the rib cage, head, and muscle weakness [4]. The number of rachitic cases continued to rise till the 1900s. By the 20th century, between 80-90% of the children living in the US and Europe were afflicted with this bone-deforming disorder [5].
A conclusive cure for rickets remained elusive until 19th century when Sniadecki, a Polish physician scientist in 1822 [6], observed that the incidence of rickets differed between children in rural areas exposed to sunlight versus those in cities, suggesting that perhaps sunlight might be involved in the etiology of rickets [7]. The 20th century gave rise to much debate surrounding the possible causal factors of rickets which was proposed to be either environmental (in the form of sunlight) or dietary in nature. In 1919, Kurt Huldshinsky [8] made significant contributions to the sunlight-rickets debate by exposing children to UV radiation from a sun quartz lamp. Much to the interest of the scientific community, the X-rays of the children exposed to UV radiation showed marked increases in the mineralization of long bones [9]. It was speculated that the skin exposure to UV rays either from the sun or lamps simulating sunlight, led to a photochemical reaction producing specific products that exerted positive effects on the skeleton. Later many others such as Hess and Weinstock in 1924 experimentally tested the impact of UV irradiation on various inert foods such as lettuce and wheat successfully imparting anti-rachitic properties [10]. In the meantime, some scientists were hypothesizing a dietary etiologic factor for rickets. In 1919, Edward Mellanby, a British biochemist and nutritionist made a landmark observation, that rickets could be induced in dogs by restricting their diet to oatmeal and then reversing the rachitic symptoms by the addition of cod liver oil [11]. This observation indicated that a nutritional deficiency is a probably contributing factor in rickets. The search for the active nutrient responsible for the therapeutic activity of cod liver oil ensued and it was presumed that Vitamin A was responsible.
In Edward Mellanby’s words, “Rickets is a deficiency disease which develops in consequence of the absence of some accessory food factor or factors. It, therefore, seems probable that the cause of rickets is a diminished intake of an anti-rachitic factor, which is either [McCollum's] fat-soluble factor A, or has a similar distribution to it” [12]. However, Elmer McCollum refuted that the antirachitic factor was Vitamin A. To test his theory, Elmer and his team conducted an experiment in 1922 wherein cod liver was aerated to oxidise fat-soluble factor A and subsequently heated. Since Vitamin A is highly sensitive to oxidation and heat, it was consequently destroyed in the tested sample of cod liver oil. When fed to rats with xerophthalmia and rickets, findings revealed that cod liver oil maintained its anti-rachitic properties although it lacked Vitamin A’s therapeutic impact on xeropthalmia [13]. This phenomenal observation led to the discovery and naming of a new vitamin, Vitamin D. This dichotomy between the separate etiologic factors, namely UV radiation, and diet, served as an impetus to scientifically trace the common denominator. The quandary was settled independently by Harriet Chick [14] and Harry Steenbock [15] at the University of Wisconsin. Steenbock, prompted by this dichotomy, ran a series of experiments, irradiating rats with UV light. He found that the consumption of special foods such as cod liver oil coupled with UV radiation showed an interesting potency to cure rickets [15]. Furthermore, he explained that the anti-rachitic activity was found in the non-saponifiable lipid portion of Vitamin D. The lipid fraction was discovered to be present in diet and skin in the inactive form that can be activated by exposure to UV light [7, 16]. This discovery led to the rapid eradication of rickets as food companies began to fortify foods rich in fats like milk to enhance its anti-rachitic characteristics through irradiation. At this time, however, the chemical makeup of vitamin D was still unknown. Researchers in the 1930s were studying the various members of the cholesterol family in hopes of identifying the chemical structure of Vitamin D [17]. Eventually, Adolf Windaus who was working extensively in clarifying the structures of various sterols, elucidated that 7-dehydrocholestrol is the precursor of vitamin D in the skin [18]. Windaus named the newly found form of vitamin D vitamin D3. In 1928, he received the Nobel Prize for his work on sterols and the vitamins associated with them. By 1930s, chemically synthesized forms of vitamin D, such as vitamin D3 was available. This opened the door for research to shed light on the various active forms of vitamin D, its metabolism, biological roles, serum levels, recommended amounts for optimal health and sources of vitamin D.
Types of Vitamin D
Vitamin D, or calciferol, constitutes a group of fat-soluble seco-sterols. Vitamin D analogs encompass both natural and synthetic forms of the vitamin, each with distinct chemical compositions and origins, with the two primary variants being vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) [19]. The natural analogs, or vitamins, include Vitamin D1, D2, D3, D4, and D5. Vitamin D1 is a molecular compound of ergocalciferol (D2) and lumisterol in a 1:1 ratio [20].
Vitamin D2 primarily derives from plant-based sources such as mushrooms and fortified foods. It is largely synthesized commercially by irradiating ergosterol, a sterol in certain fungi and yeast, with ultraviolet light. Following ingestion, vitamin D2 undergoes hydroxylation processes in the liver and kidneys to produce calcitriol, the biologically active form of vitamin D2, albeit with lower efficiency than the other common form of vitamin D, vitamin D3 [21].
Contrary to vitamin D2, vitamin D3 is predominantly sourced from animal products and synthesized endogenously in the skin upon exposure to ultraviolet B radiation. The synthesis begins with converting 7-dehydrocholesterol in the skin to pre-vitamin D3, subsequently transforming into vitamin D3. This endogenous production mechanism is highly efficient and serves as the primary source of vitamin D3 for human populations [22].
Both vitamin D3 and D2 are commercially synthesized and can be found in supplements or fortified foods. Despite differences in their side chain structures, the metabolic pathways of D2 and D3 remain unaffected, with both forms serving as prohormones upon activation [19]. Moreover, both variants exhibit efficient absorption within the small intestine, achieved through straightforward passive diffusion and a mechanism mediated by carrier proteins in the intestinal membrane [23].
A recent systematic review of randomized and non-randomized controlled studies involving a total of 1,277 healthy human participants from 24 studies investigated the comparative effectiveness of vitamin D2 and D3 in increasing the concentrations of vitamin D metabolites in the bloodstream and influencing various functional indicators, such as serum parathyroid hormone (PTH) levels, isometric muscle strength, hand grip strength, and bone mineral density. The results indicated a notable difference in efficacy between cholecalciferol and ergocalciferol. Cholecalciferol demonstrated higher effectiveness in improving total 25-hydroxyvitamin D (25(OH)D) levels and reducing PTH levels compared to ergocalciferol. Further analysis through meta-regression revealed that the difference in efficacy between cholecalciferol and ergocalciferol was less pronounced at lower doses. Interestingly, the average daily dose emerged as a significant predictor of effect size, suggesting that dosage plays a crucial role in determining the magnitude of the intervention's impact [24].
In addition to vitamin D2 and D3, there are less studied forms, such as vitamin D4 (22-dihydroergocalciferol) and vitamin D5 (sitocalciferol). Vitamin D4 is structurally similar to D2 and D3 and is found in fish liver oils and certain mushrooms. However, its physiological significance is less researched. Similarly, vitamin D5 is found in specific plant sources, but its biological activity and metabolism are poorly understood compared to D2 and D3. Alongside natural forms, synthetic analogs of vitamin D, including Maxacalcitol, Calcipotriol, Dihydrotachysterol (DHT), Paricalcitol, Tacalcitol, Doxercalciferol, and Falecalcitriol, offer various therapeutic potentials and applications, expanding the utilization of vitamin D in healthcare [20].
Biology of Vitamin D
Vitamin D is comprised of an active form, calcitriol, which binds to the vitamin D receptor (VDR), which is a specialized protein that is commonly found in some specific cells within their nuclei. The VDR operates as a transcription factor due to the binding interaction, which prompts the expression of numerous genes that play a key role in crucial processes such as calcium absorption, which occurs in the intestines [25]. The VDR is expressed in a range of organs across the body, considering the fact that it is a member of the nuclear receptor superfamily, which is indicative of the active role that vitamin D plays in physiological functions [26]. In order for the body to maintain and optimize calcium and phosphorus levels within the bloodstream, VDR is usually activated in crucial cells in the bones, parathyroid gland, and intestines, together with other crucial hormones such as calcitonin and parathyroid hormone.
Bone density and integrity regulation in addition to overall skeletal health, are optimized through VDR activation, even though its impact also facilitates crucial functions in immune functioning and cellular proliferation. The impact of vitamin D on bone health and well-being is associated with the occurrence of conditions like rickets in situations where there is a deficiency of the vital nutrients, especially during the formative years of early childhood. The role of vitamin D in immune regulation is evident considering the fact that monocytes and T lymphocytes in addition to some other white blood cells, express VDR [25]. Bone metabolism is also a crucial process that is attributable to VDR, even though the vitamin also impacts crucial physiological processes such as tyrosine hydroxylase gene expression within adrenal medullary cells [27]. Vitamin D also facilitates the synthesis of neurotrophic factors and hence highlighting the extensive role it plays in both homeostasis and cellular function.
The influence of vitamin D on vascular function and its regularization of blood pressure enhances cardiovascular health [26]. The biological activation of vitamin D is initiated by hydroxylation in the liver to convert it to 25-hydroxyvitamin D, and a second hydroxylation occurs in the kidneys to further convert it into its active form, which is crucial for exerting the effects of vitamin D receptors after binding with them [28]. The stimulation of calcium-binding proteins to facilitate the transportation of the vital mineral into the bloodstream from intestinal epithelial cells is enhanced by vitamin D, which is crucial for facilitating calcium homeostasis [29]. VDR is also vital for enhancing cell growth and differentiation in the body by regulating gene expression that is vital for cell cycle control and cellular differentiation, which may lead to benefits such as the exertion of anti-cancer effects.
While the parathyroid hormone and blood phosphate levels play a key role in regulating the conversion of vitamin D to its active form, the synthesis of the vital nutrient is regulated by numerous factors which include latitude, skin pigmentation, and seasons. Vitamin D status is best assessed by the evaluation of serum levels with sufficient levels typically being above 30ng/mL, while inadequate levels being anything that is below 20ng/mL [30].
Recommendations on Serum Levels of Vitamin D
Depending on factors like age, sex and others, different authorities have different recommendations for appropriate serum levels of 25(OH)D [48]. Many vitamin D specialists believe that blood 25(OH)D concentrations above 100 nmol/L are ideal for all health outcomes, including bone [31]. According to an analysis published in 2014, blood levels of 25(OH)D that were most beneficial for all outcomes seemed to be around 30 ng/mL (75 nmol/L) [32]. For age group 1- 70 years, World Health Organization (WHO) recommends an intake of 200 IU/d, and European Food Safety Authority (EFA) recommends 600 IU/d [33]. According to the Endocrine Society, adults may require around 1,500–2,000 IU of vitamin D per day, while children and adolescents may require at least 1,000 IU per day in order to maintain blood 25(OH)D levels above 75 nmol/L (30 ng/mL) [34]. On the other hand, the government of the United Kingdom advises its residents who are four years of age and older to consume 10 mcg (400 IU) daily [47]. The Endocrine Society deemed a level of up to 250 nmol/L to be safe and suggested a preferable range of 100–150 nmol/L for 25(OH)D [34]. Additionally, the Endocrine Society determined that vitamin D intoxication is a very uncommon condition that is typically not noticed until blood levels of 25(OH)D exceed 375 nmol/L [35].
During pregnancy, IOM (a), EFSA (b), SACN (c), and WHO (d) recommended an intake of 600 IU/d (a &b), 400 IU/d (c), and 200 IU/d (d) of vitamin D, respectively [33, 47
