Category: Vitamin D

Vitamin D, or calciferol, is a vitamin present naturally both in some sources of food and produced endogenously in the skin, and is a key component in many different biological pathways in the body. Foods rich in vitamin D include fish, red meats and egg yolks. Since its discovery, through the work of Mellanby and separately McCollum, there have been many studies on vitamin D and its potential applications in medicine, with over 50000 studies and articles being published since 1922. There is currently great scientific interest surrounding this vitamin, there have been reports of using it to assist in the treatment of Covid-19. However, other studies dispute the efficacy in combatting Covid-19. This short essay will explore the physiological effects of vitamin D, whilst also examining what can happen in those with serious vitamin D deficiency, and how individuals with a deficiency may be treated.

Production and Physiological Effects of Vitamin D

Vitamin D is technically not a vitamin, due to the body’s ability to produce it when ultraviolet light penetrates the skin. Instead, it is better described as a type of fat-soluble steroid hormone. When ultraviolet (B, wavelengths 290-315nm) radiation is absorbed by the skin a molecule called 7-DHC, which is mostly concentrated in the lowest layers of the epidermis, is synthesized into an isomer of vitamin D3 (also called cholecalciferol) named preD3. Next, a protein called VDBP will carry D3 into the bloodstream through capillaries, after isomerization of preD3 into D3. This reaction requires a body temperature of around 37C and will last for around three days even if there is no exposure to the sun again during that time. D3 is then transported to the liver, where it is hydroxylated into 25(OH)D3, which in turn can either be stored or circulated in blood plasma. This intermediary metabolite acts as a type of reservoir, in which a second hydroxylation reaction can occur in the kidneys forming 1,25(OH)2D3, the active form of D3. Individuals with higher skin melanin content, those who are obese and those who are older produce less vitamin D via sunlight exposure, in addition to numerous other factors also lowering its production.

As mentioned previously, vitamin D can also be found in a small number of foods. The main source of dietary vitamin D is in fish, however there are vast differences in vitamin D content across different types of fish, with oily fishes such as salmon containing higher concentrations. A second type of vitamin D, vitamin D2, is present in some other foods, namely plants and mushrooms. They produce D2 (also called ergocalciferol) via the irradiation of ergosterol, a sterol comparable to mammalian cholesterol in that it helps to maintain the structure of the cell membrane. A clinical trial, performed by Trang et al. (1998, pp.854-856), examined the differences in the effect of D2 and D3 on increasing 25(OH)D. The trial was carried out between February and May, when 25(OH)D levels were deemed to be at the lowest concentrations during the year. 34 volunteers were assigned to a double-blind group, where they would take either D2 or D3. Remaining volunteers were assigned D3 or to no vitamin at all. The results shown, despite the small sample (n=89), are reasonably reliable as p = 0.03. We can conclude from these results that while both D2 and D3 showed a dramatic increase in 25(OH)D levels, D3 showed the larger increase.

Vitamin D has two major effects, which have different functions in the body. Firstly, it regulates calcium metabolism. The main way it achieves this is by raising the amount of calcium absorption in the intestine. Enterocytes are a form of simple columnar epithelial cell in the intestine which are stimulated by the hormonally active 1,25(OH)2D3, to further increase the rate of calcium transportation along the cell. Calcium metabolism is also regulated through bone resorption. The second major effect that vitamin D has on the body is through the binding of 1,25(OH)2D3 to the VDR, a transcription factor, where it acts as a ligand. VDR is present on the surface of most immune cells. An example of how 1,25(OH)2D3 can help with the immune system is in B-lymphocytes, where apoptosis of activated B-lymphocytes is increased and T-lymphocyte activation is decreased. We can therefore deduce that 1,25(OH)2D3 plays a pivotal role in regulating the immune system which may help in cases of autoimmune. VDRs also help to increase and maintain muscle strength. There have been multiple studies in which the VDR gene in mice is blocked, causing atrophy in the muscles. The way in which VDR affects muscular function is not entirely clear and more research needs to be done.

Effects of Vitamin D Surplus or Deficiency

In the recommended daily intake of vitamin D is 400IU, equivalent to 10mcg. This dosage is recommended during the fall and winter months, as less vitamin D will be synthesized from sunlight during this time. A safe level is around ten times the recommended intake (4000IU), but ingesting any more of this would put an individual at risk of hypercalcemia, meaning calcium levels in the blood are above a safe level. Side effects of this can weaken bones, cause issues with the kidneys, and in more serious cases damage the heart and brain, causing a threat to life.

A diet consisting of less than 400IU of vitamin D a day can result in deficiency. The main disorders caused by vitamin D deficiency are generally seen in the bones. Two examples of disorders are rickets, which mainly affects children, and osteomalacia which is a similar condition, but generally found in adults. Rickets can usually be observed by the presence of bowlegs, a bending outward of the legs. Due to many foods being fortified and better nutrition, rickets has mainly become a thing of the past in the Western world. Children with rickets also have growth problems and an increased diameter of the wrists, all caused by the weakening of epiphyseal growth plates. In a small number of cases, rickets can be inherited via any form of genetic conditions, such as a kidney disorder, that affect vitamin D content in the body. Osteomalacia is caused by a lack of mineralization in the bones, following the closing of growth plates. Both osteomalacia and rickets can cause painful bone sensations and individuals with said conditions may experience more bone fractures.

In a large proportion of individuals (around 60-70%) are considered to have insufficient vitamin D intake, meanwhile around a sixth are vitamin D deficient. If you are considered to have vitamin D levels in the insufficient or deficient range, then treatment is required.

Conclusion

Vitamin D is a vital component of many different biological pathways. It helps with bone and muscle maintenance as well as regulation of calcium levels and the immune system. The consumption of vitamin D has greatly increased over the past hundred years, leading to a decrease in those with a deficiency. There are still risks of vitamin D deficiencies due to a multitude of factors, including diet, environment and age. The associated complications are often painful and can cause serious issues if not attended to. In many people do not ingest the 400IU of vitamin D recommended as a minimum level by the NHS in the winter months. It is important that an individual maintains a healthy level of vitamin D in their body, and more people are now taking supplements to achieve the required amount. It is still a topic many are unaware of, and more public campaigns would be useful.

The method of applying nutrients or non-nutrient bioactive ingredients to edible items is known as fortification. By using current distribution systems for industry-manufactured goods, food fortification raises micronutrient availability to minimize nutritional shortages in the population. Fortification is the best opportunity to increase vitamin D supply to the public. Food fortification offers the greatest way to improve the population’s vitamin D intake. Around the time of the World Wars, fortification of many micronutrients became popular to avoid micronutrient malnutrition and to fix nutritional shortages during food production.

Vitamin D, also known as calciferol, is a fat-soluble vitamin that is not naturally present in many foods, but is fortified in many foods and available as a dietary additive. When UV rays from the sun penetrate the skin, they induce vitamin D synthesis, which is the primary way our bodies receive it. The small intestine is where it is utilized. Vitamin D must be hydroxylated twice before it can be absorbed and used by the body. The first hydroxylation occurs in the liver. Vitamin D is transformed into hydroxyvitamin D. The resulting hydroxylation, which occurs mostly in the kidney, yields the physiologically active ‘calcitriol’ (Institute of Medicine, 2010). Vitamin D aids calcium synthesis in the intestines. Individuals who have insufficient sun exposure, reduced oral consumption, or poor intestinal absorption are generally at risk for vitamin D deficiency (Holick, Chen, Lu and Sauter, 2007). The easiest way to assess vitamin D sufficiency is to calculate the 25-hydroxyvitamin D content in the blood. Average daily vitamin D consumption in the general population and existing dietary reference intake values are often insufficient to sustain optimum vitamin D levels (Kennel, Drake and Hurley, 2010). Vitamin D is also well-known for its interaction with calcium. Calcium is critical for preserving healthy bones and avoiding the development of osteoporosis. It allows the intestine to absorb the calcium we ingest. Osteoporosis is a debilitating condition caused by a lack of calcium. The bones of the body grow fragile and porous. It is known as ‘the invisible disease’ and there are no signs or symptoms until anyone threatens to break bones. This disease, on the other hand, is far from invisible. The effects of undiagnosed and untreated osteoporosis are catastrophic. Bone is a living tissue that is constantly removed and substituted. Bones include natural sex hormones, calcium, vitamin D, enough calories, proteins, and weight-bearing strengthening activity to remain healthy (Sahota, 2000).

It is recommended that babies from birth to the age of 1, if breastfed, should be given a vitamin D supplement of 5 mcg daily. This is recommended due to their rapid growth during this short period of time. Babies from birth to the age of 1 who are formula fed do not need any supplementation as formula is usually fortified with vitamin D. These recommendations are for healthy term babies (INDI, 2020). The current minimum dietary daily amount of vitamin D is 5 mcg. Food, including supplements, need to provide 10 mcg of vitamin D daily for everyone over the age of 5 years. In older adults, aged 65 and over, supplementation is needed. For healthy older adults who get sunlight outdoors each day, should take a 10 mcg supplement from October to March. People with naturally darker skin should be taking 10 mcg all year round as their dark complexion makes it harder to absorb vitamin D. Housebound older adults should be taking 15 mcg all year round, as they are not exposed to UV rays. The FSAI is intended to discuss the vitamin D needs of other ‘at-risk’ populations, such as pregnant women and children aged 12 months to five years, at a later date (FSAI, 1999). Last reviewed in 2020.

Since 2007, many widely consumed foods have been supplemented with vitamin D on a voluntary basis. Milks, yoghurts, and breakfast cereals are examples of these foods. However, only people who eat fortified forms of these items get more vitamin D and the fortified forms are limited to a few brands. Avonmore Super Milk is the most well-known and is advertised regularly. A 250ml glass of Avonmore Whole and Low Fat Super Milk contains 100% of the recommended daily intake of vitamin D, as well as many other micronutrients. Vitamin D fortification projects introduced in the United States and Canada have strengthened these countries’ vitamin D status. In February 1927, Quaker Oats obtained the first license to produce vitamin D-enriched oats. Pharmaceutical firms were awarded licenses to produce a therapeutic vitamin D medication. This method had been expanded by 1934 to manufacture vitamin D fortified milk. Soon, vitamin D fortification was accomplished at a low cost by directly applying vitamin D to milk. In Australia, margarine, as well as milk and yoghurts, are now fortified with vitamin D. In New Zealand, fortification of margarine is not required, but voluntary fortification of fats and products has been allowed since 1996. Margarine and margarine-like spreads are the only items in the UK that are allowed by law to contain vitamin D.

The cost of doing nothing is huge. In infants and children, rickets is a huge risk. Rickets in children are caused by a deficiency of vitamin D and a lack of exposure to sunlight. Vitamin D deficiency is also a problem in older children and teenagers (Wagner and Greer, 2008). Rickets, long believed to be extinct, is reappearing. Bone growth in children is affected by rickets. Bone pain, slow growth and fragile bones contribute to bone distortions. Children may be born in rare circumstances of inherited ricket types. It may also occur if another disease inhibits the body’s absorption of vitamins and minerals, like coeliac disease. Rickets can be treated effectively for most children by consuming foods containing calcium and vitamin D, or vitamin supplements. A diet that includes vitamin D and calcium, spending some time under the sun and, if necessary, taking vitamin D supplements, can easily prevent rickets (Chick et al., 1922). Symptoms include pains in bones, dental problems, fragile bones prone to fractures, and stunted growth.

Adults can experience a similar condition, which is known as osteomalacia or soft bones. Osteomalacia is a bone weakening condition. Osteomalacia is a bone condition caused by a lack of mineralization in the skeleton. Types that require vitamin D must be differentiated from hypophosphatemic types. Bone pain, muscle fatigue, and fragility fractures are common signs and symptoms. Serious fragility fractures in the pelvis, sacrum, lower arms, and legs are strong signs of osteomalacia (Tiefenbach, Scheel and Maier, 2018).

Adults can also develop a condition called osteoporosis. Osteoporosis is similar to osteomalacia. Osteomalacia is a problem with bones that do not harden, whereas osteoporosis is a problem with bone weakness. Osteoporosis is caused by a decrease in bone density, and osteomalacia caused by impaired mineralization. Because of the secondary complications of a bone fracture, 20% of people aged 60 and over who break their hip will die within 6 to 12 months. When an individual over the age of 60 breaks their hip, half of them lose their rights and independence. They would be unable to bathe, shave, or simply walk about the room without help. Only 15% of people in Ireland suffer from bone loss, leaving 280,000 people without a diagnosis and at risk of losing their freedom. These statistics emphasize the importance of people taking care of their bone health and determining whether they are at risk. It is estimated that up to 300,000 Irish people have osteoporosis. While it is more frequent in menopausal females, it may also affect men.

This puts a huge impact on our health system, as well as the citizens of Ireland. In order to improve the situation educating the population is critical. Education is key from a young age as individuals reach their peak bone mass before aged 30. Education in primary schools and post primary schools is essential to make children and teenagers aware of the situation and how to rectify it. Third level students should also be educated on the topic. TV adverts or public health leaflets can be used as a means to educate the older population.

Studies in Ireland have shown that low vitamin D intake and vitamin D deficiency are widespread in the population of Ireland. Due to our geographic location, and multiple combinations of factors that adversely affect vitamin D intake in the population, most of us should be taking vitamin d supplements. People of every age at risk of developing bone disorders due to vitamin D deficiency. Education is the best and most effective way of improving the situation. This problem does not just put a burden on our health system, but also on the people of Ireland.