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Vitamin D

The NHS recommends that everyone in the UK take a vitamin D supplement between October and March. Recently, lowered levels of this vital vitamin have been A DEEPER implicated as one possible reason why COVID-19 takes a disproportionate toll on the understanding of BAME community. Jordi Mascio of Goldman Laboratories takes an in depth look…

VITAMIN D

ALMOST everyone is familiar with vitamins, either as food supplements or as dietary essential factors. Ever since the discovery that limes prevented scurvy on sailing voyages, we’ve known that some diseases are caused by vitamin deficiency and can be treated by adding these vitamins to our diet. However, a thorough understanding of the mechanism of how vitamins work has sometimes eluded us.

Terminology

The terminology regarding vitamin D may be somewhat confusing, even to trained doctors. Vitamin D is not a single substance. Vitamins occur in a variety of related forms known as vitamers. A vitamer of a particular vitamin is one of several related compounds that exhibit biological activity against a specific vitamin deficiency. Nutrition research has shown that all vitamers exhibit biological activity against their specific vitamin deficiency, although different vitamers exhibit different potencies against those diseases.

When it comes to Vitamin D, the most common forms are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The latter is produced in the skin following exposure to ultraviolet light including sunlight. It is converted in the liver to calcifediol (25-hydroxyvitamin D) which is then converted in the kidney to calcitriol (1,25-dihydroxyvitamin D). Calcifediol is considered to be a non-active form of vitamin D, so only calcitriol can be used by the human body. The biological influence of this hormone is vast as evidenced by the extensive expression of the Vitamin D Receptor (VDR) in many organ tissues.

factors affecting viamin d levels

Vitamin D is produced by the skin from the provitamin D 7-dehydrocholesterol upon exposure to direct sunlight or artificial UVB light. This endogenous way of producing vitamin D is somewhat hampered by recent changes in lifestyle as human spend more time indoors and are less exposed to sunlight. Concerns regarding the adverse effects of exposure to sunlight or UV-B light, such as skin cancer and photo-aging have further increased the prevalence of vitamin D deficiency. Other factors may affect levels of vitamin D, such as race, latitude, season and time of the day exposure to sun, and the use of sun cream.

Those who live further north have reduced levels of vitamin D in their bodies. People with darker skin tone have been shown to have lower levels of vitamin D compared to people with lighter skin tones. Recent research have found that although they have lower levels of vitamin D, they don’t have the associated deficiency diseases such as hyperparathyroidism or hypocalcaemia. The likely explanation is that they have a genetic polymorphism that results in lower levels of vitamin D-binding-protein, so that the bioavailable vitamin D is equivalent to those with lighter skin. The production of circulatory active forms of vitamin D is dependent on good liver and kidney function. Previous studies have shown the increased incidence of vitamin D deficiency in found with many types of liver disease, including Hepatitis C virus (HCV) liver disease, nonalcoholic fatty liver disease (NAFDL), cirrhosis and autoimmune liver disease such as primary biliary cirrhosis (PBC). Vitamin D homeostasis is also affected with people with chronic kidney disease (CKD), and they are more prone to vitamin D deficiency. This has led to the recommendation by many health organisations for vitamin D dietary supplementation in patients with these issues.

vitamin d: the impact on organs systems

After understanding the basic homeostasis of vitamin D, one must understand its effect on different organ systems. Biological influences are mediated by the Vitamin D Receptor which is a present in more than 36 organs. When the membrane VDR binds vitamin D, a cellular cascade is initiated that leads to the down-regulation or up-regulation of different genes. One of the most important roles of vitamin D is in calcium and bone homeostasis. Calcium absorption by the intestine is through a passive paracellular pathway and an active transcellular pathway. Vitamin D is a main regulator of the active transcellular absorption pathway in the intestine. Its effect on bone homeostasis is not limited to its effect on calcium absorption but also in its direct effect on osteoblasts. The Vitamin D Receptor is present in osteoblasts, and vitamin D promotes differentiation and mineralisation of bones. This means that children with low levels of vitamin D are at risk of developing hypocalcaemic rickets, an awful yet preventable disease. In 2017-18, there were 101,136 hospital admissions where vitamin D deficiency was a primary or secondary factor in the admission, a rise of 34 per cent in a year, analysis of NHS Digital data shows. Poor nutrition and food poverty have also led to cases of gout and scurvy jumping by 25% in the same period.

Aside from rickets, low Vitamin D levels leave these children are at risk of developing seizures and cardiomyopathy. Post-menopausal women are at increased risk of osteoporosis and subsequent bone fractures. Vitamin D supplementation reduces that risk by it is negative effect on osteoclasts. Some research studies suggest that vitamin D supplementation might also reduce the risk of early menopause.

Increasingly, scientific data is accumulating that highlights the correlation between vitamin D deficiency and diabetes. Research has shown that Beta-cells in the pancreas express Vitamin D Receptors. Vitamin D treatment had been shown to improve glucose tolerance in insulin resistance.

Vitamin D may have also have an effect on the immune system and the development of autoimmune disease. Its effect has been proven on both B cells and T cells. Treatment with vitamin D inhibits the maturation and differentiation of dendritic cells, resulting in increased tolerance for autoimmune diseases. All the benefits and mechanisms mentioned above are probably only the tip of the iceberg. With the use of more advanced research methods, evidence is accumulating regarding the positive effects of this vitamin. Most recently, vitamin D has grown in public awareness as some research has shown that vitamin D treatment may reduce morbidity and mortality in COVID19 patients. Therefore, there has been increased interest in improving vitamin D status by either recommending vitamin D supplement use or fortifying foods with vitamin D. This objective might be achieved relatively easily, as vitamin D supplements are already available in the market. With all this, one might wonder why the testing and prescription of vitamin D by practitioners is not a routine practice. Should it become one? n

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JORDI MASCIO has more than 14

years’ experience in the Bio Medical

industry both in highly technical positions

and in distribution and managing roles. He

holds an MSc in Bio Medical engineering and

an MSc in Molecular Physics. He provides

courses and seminars on liposomes and

innovative molecules to many practitioners

around Europe. Find out more at

www.goldmanlaboratories.com.

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