Vitamin D is a very interesting, unique and important fat soluble vitamin. It is important because of the role that it plays especially in having healthy strong bones and teeth. It does so by helping the body absorb calcium, one of the main building blocks of bone.

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Vitamin D is fat soluble

Recently, we have been hearing a lot about vitamin D being the miracle vitamin. It has become the nutrient of the year. Across the media, there has been much mention of vitamin D and some really good and interesting news about it.

In truth, vitamin D is not a vitamin, rather it is a hormone with a similar structure to steroid hormones like oestrogen and testosterone. The healthy and natural way to get it is from sunlight, which is why it is also known as the “sunshine vitamin”. We can get 90% of our vitamin D from exposure to ultraviolet B (UVB) rays. Vitamin D is synthesised in the human skin upon exposure to sunlight and then gets metabolised in the liver and kidneys into its active form. However, many of us are not getting enough of this essential vitamin. It is worth noting that approximately 2 in 5 of the UK population have low vitamin D levels, defined as serum levels below 30 nano-moles per litre (nmol/L). When vitamin D3 in the skin is inadequate due to insufficient exposure to UVB radiation, oral intake of vitamin D is necessary to meet vitamin D requirements.

Sources of vitamin D:

How vitamin D is made in our bodies:

Most of the world relies on exposure to the sun for their vitamin D synthesis and that is first step needed to maintain adequate levels. The synthesis of active vitamin D in our body is a pretty complicated process. It has to start with sun, and if you have to have good liver and good kidney functions, you end up with the active form of vitamin D. Our skin contains a certain type of cholesterol which, when stimulated by UVB rays from the sun, forms vitamin D3 in the skin. This is the first form of vitamin D, which is biologically inactive, but then goes through further processes in the body. The next step is conversion in the liver where a form is produced which is a little bit active. Finally it reaches the kidneys where it gets converted to its most active form, 25?hydroxyvitamin D3 (25?OHcholecalciferol), which is most beneficial for the body.

However, this process can be inhibited many ways. Where you live, the season, and the time of day affect how much sunlight reaches your skin. The farther you live from the equator, the less UVB radiation you receive, and it is UVB that initiates the production of vitamin D in your body. During the winter months, the earth tilts away from the sun, increasing the angle at which the sun’s light reaches the earth’s surface, and when this happens, it lowers or eliminates the amount of rays that can reach a person’s skin. People who live at latitudes greater than around 37 degrees north or 37 degrees south can not make vitamin D from sunlight during the winter because of the angle of the sun. In between these latitudes, whether north or south, our bodies can make it all year round as the sun shines directly overhead for much of the year.

Apart from environmental conditions, age, skin colour, how much skin is exposed, and use of sunscreen all influence the production of vitamin D in one’s skin. All of these factors mean that some of us may be getting less vitamin D than our bodies need. For example, application of sunscreen with an SPF factor of 10 reduces production of vitamin D by 90%.

Food sources:

Dietary sources of vitamin D are limited. Fortunately, most people do not have to rely on their diets for vitamin D. Its primary natural source is sunlight, not food. While oily fish is the main food source of vitamin D, other good sources D are:

• Fish (per 100 g serving) such as salmon (687 IU), tuna (544 IU), sardines (222 IU), halibut (162 IU) and mackerel (340 IU);
• Fortified milk provides 100 IU of vitamin D per 237ml. However, dairy products made from milk are not always fortified with vitamin D and typically contain only small amounts;
• Fortified breakfast cereals, bread and some juices (e.g. a cup of orange juice provides 137 IU), yogurt, margarine, and soy beverages;
• One tablespoon of cod liver oil provides 1360 IU;
• One large egg yolk (41 IU);
• Beef, liver, kidney, and cheese also provide small amounts;
• Mushrooms exposed to sunlight or UV light provide some vitamin D. You can do this yourself by popping a punnet of mushrooms underside up on a windowsill for 1-2 hours between 10 am-3 pm on a sunny day.



The active form of vitamin D can directly or indirectly regulate 100-1250 genes involved in skeletal or other biological functions. As a hormone, vitamin D’s most dramatic effect is to facilitate intestinal absorption of calcium, but it also stimulates absorption of phosphate and magnesium ions. It has an important role in regulating calcium and phosphorus metabolism and their body levels, and thereby mineralisation of bone. Vitamin D is also essential for many non-skeletal effects, particularly on neuromuscular functions. Muscles need vitamin D to move and nerves need it to carry messages between the brain and the rest of the body. It is also necessary for the immune, endocrine and cardiovascular systems. Vitamin D can also regulate cell differentiation and growth.


Current UK guidelines for vitamin D supplementation came in an advisory in July 2016 from Public Health England (PHE) to the government, stating that to protect bone and muscle health, everyone—all adults and children over one year—needs a vitamin D equivalent to an average daily intake of supplement containing 400 IU (10 micrograms), particularly in autumn and winter as daylight hours are reduced.


Vitamin D Deficiency:

It is currently estimated that about a billion people worldwide are probably vitamin D deficient, which is going to have health implications because there is a long list of things that vitamin D may be good for. Maintenance of serum concentrations within a narrow range is vital for normal functioning of the nervous system, as well as for bone growth and maintenance of bone density. In vitamin D deficiency, calcium absorption can not be high enough to meet the body’s calcium requirement.

People can become deficient in vitamin D because they do not consume enough or absorb enough from food, their exposure to sunlight is limited, or their kidneys cannot convert vitamin D to its active form in the body. Deficiency can result in rickets, soft bones, and seizures or heart failure as a result of a lack of calcium (low calcium heart failure). In these cases, calcium is mobilised from the bones to maintain normal serum calcium levels. Vitamin D deficiency can present differently in adults and children.

In children:

Vitamin D deficiency causes bone deformities and rickets, a condition in which the bones become soft and bend. It is a rare disease, but still occurs, for instance among black, Asian and minority ethnic group (BAME) infants and children. Rickets was eradicated from the UK during the second world war, but has returned to England and other western countries through immigration by high risk populations.

In adults:

Vitamin D deficiency leads to a condition called osteomalacia (soft, brittle bones) causing bone pain and muscle weakness and increased risk of osteoporosis and greater risk of fractures. For adults with low or suboptimal levels of vitamin D, there may be no symptoms at first; it is therefore important to know your risk status and take measures to prevent deficiency developing. The body needs calcium for many functions, from nerve signal transmission to blood vessel health and building and strengthening bones. This function is especially critical after the menopause. Vitamin D is essential for the efficient use of calcium by the body. In other words, vitamin D and calcium are another natural duo, working together, therefore, they should be taken together. It is recommended that individuals obtain calcium from their diet, getting only the necessary amount and not taking excess calcium.

Factors that may contribute to vitamin D deficiency:

Obesity: a BMI of over 30 increases the risk of vitamin D deficiency because the vitamin D gets stored in the body fats, which prevents it from getting into the blood.
Magnesium deficiency: recent findings suggest that high magnesium intakes may reduce the risk of vitamin D deficiency. Magnesium helps activate the vitamin so the body can put it into use, which would explain how magnesium deficiency negatively affects vitamin D status. Therefore magnesium rich foods are important in your diet.
The elderly: the elderly have a reduced capacity to synthesise vitamin D in their skin when exposed to sunshine and are more likely to stay indoors or use sunscreen, which prevents vitamin D synthesis. It has been estimated that across Canada, the US, and Europe, the prevalence of vitamin D deficiency ranges between 20%-100% in free-living elderly people. Furthermore, institutionalised adults who are not given vitamin D supplements are at extremely high risk of vitamin D deficiency. Daily supplementation of vitamin D is especially important for older adults. People aged 71 and over should get 800 IU (20 mcg) daily. But many experts believe that is too low, and are now recommending 2000 IU/day for those with low blood levels.
Other groups: all babies and pregnant women, people who practice whole body clothing, people with restricted diets lacking in calcium, as well as people with chronic kidney disease or inflammatory bowel disease may all carry a risk of vitamin D deficiency.

Points to note:

When possible, get your vitamin D from foods and from modest sun exposure, making sure to avoid sunburn. Recommendations suggest having five to ten minutes of sun exposure, enough to cause slight pinkness of the skin, maybe two to three days of the week to the face, arms, legs, or back without sunscreen. This will enable you to make enough of the vitamin in the middle part of the day (10 a.m. to 3 p.m.). This is because the sun’s rays are most direct between these hours. The Department of Health (DoH) reveals that in the UK the sun rays are only strong enough to make vitamin D via exposed skin in our hands, face and arms and legs from April to September.

Vitamin D deficiency is most common in people with dark skin (i.e. BAME groups). People with dark skin need to spend longer time in the sun to produce the same amount of vitamin D as those with lighter skin, because their skin has less ability to produce vitamin D from the sun.

Forms of vitamin D and supplements:

The best way to be sure of a healthy vitamin D status is to take a supplement. Vitamin D comes in two forms: D3 (cholecalciferol) and D2 (ergocalciferol). Vitamin D3 is the form made naturally in the body, in the human skin from cholesterol in response to sunlight. It is also the form most often used to fortify milk and other foods, such as breakfast cereals. Vitamin D2 is another form of vitamin D photosynthesised in plants, mushrooms and yeasts.

When vitamin D3 in the skin is inadequate due to insufficient exposure to UVB radiation, oral intake of vitamin D is necessary to meet vitamin D requirements. Vitamin supplements contain either D3 or D2. If one wants to take supplements, some experts recommend choosing one that contains D3. However, a number of recent reports conclude that D2 is just as effective as D3 at the recommended dosage levels. Both forms increase vitamin D in the blood. Most vitamin D supplements available without prescription contain vitamin D3.

Average daily recommended amounts for different ages—from a group of experts—are generally given in international units (IU). For adults it is 600 IU/day. Multivitamin supplements generally provide 400–1000 IU (10–25 micrograms/mcg/?g) of vitamin D2 or vitamin D3. The most commonly available dose of separate/single-vitamin D supplement provides 400 IU/day.

The best measure of one’s vitamin D status is having a simple blood test. The results come back as in either nano-moles per litre (nmol/L) or nano-grams per millilitre (ng/mL), where 1 nmol/L = 0.4 ng/mL.

In general, if your serum 25?hydroxyvitamin D (25 OHD) level is below 30 nmol/L (12 ng/mL), you have a deficiency; levels above 125 nmol/L (50 ng/mL) are probably too high. Readings of 50 nmol/L or above (20 ng/mL or above) are sufficient for most people. The amount of vitamin D you need depends on your age. When your levels fall below 50 nmol/L, your doctor will advise you to bring these levels to the required concentrations by including more vitamin D rich foods in your diet and by taking daily supplements. It could take days, weeks or even a few months to bring your levels back up.

When choosing supplements, it is important to buy a reputable brand and to stick to recommended doses. Also, remember to add calcium to your diet, but you should get most of it, if not all, from your kitchen.


If you cannot get enough vitamin D from sunshine and/or food, over use of supplements can cause vitamin D overdose. Excessive sun exposure does not cause vitamin D poisoning because the body limits the amount of this vitamin it produces. When amounts of vitamin D in the blood become too high, it can be toxic. The signs of toxicity may include nausea, vomiting, poor appetite, constipation, weakness, and weight loss. And also by raising the calcium levels in the blood, too much vitamin D can cause confusion, disorientation, and damage to the heart and kidneys.

The "upper limit" for vitamin D is 1000 to 1500 IU daily for infants, 2500 to 3000 IU daily for children of 1-8 years, and 4000 IU daily for children of 9 years and older, adults, and pregnant and lactating teens and women.

If you do take more than 1000 IU daily, be sure to stay well below the safe upper limit of 4000 IU/day (100 mcg/day). It has been suggested that vitamin D has a wide range of benefits on health outcomes, and yet the potential benefits of higher amounts remain controversial. Randomised clinical trials have not yet produced definitive results.

Interactions — medications affecting vitamin D status:

Vitamin D may interact or interfere with other medicines or supplements you might be taking. For example:

Corticosteroid, prednisone and anti-inflammatory medicines all impair how the body handles vitamin D, which leads to lower calcium absorption and subsequent associated problems as highlighted above,
Cholestyramine, the cholesterol-lowering drug can reduce the absorption of vitamin D and the other fat-soluble vitamins A, E, and K.
• Anticonvulsants, both phenobarbital and phenytoin, used to prevent and control epileptic seizures, increase the breakdown of vitamin D and reduce calcium absorption.
• The TB drug rifampin and some HIV medications should not be taken at the same time as vitamin D because they can either decrease the absorption of vitamin D or increase its metabolism, either of which may lower vitamin D blood levels.


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