Vitamin D: The Sunshine Vitamin

7-minute read•July 11th, 2018

Calling it ‘the sunshine vitamin’ might sound like a joke. It’s not. Vitamin D is produced in your body when you’re exposed to sunlight. That alone makes it special among vitamins. Involved in regulating important processes around the body, including its own production, vitamin D is one to keep an eye on.

Here’s all you need to know about it.

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What is vitamin D?

Vitamin D, or calcitriol, belongs to the group of fat-soluble vitaminsVitamins can be fat-soluble and water-soluble. Vitamin D is fat-soluble. This means that it is absorbed with the help of lipids (fats) and is less likely than water-soluble vitamins (e.g. like B and C) to leave the body through the kidneys. In foods and supplements it comes in two forms: as D₂, ergocalciferol, and D₃, cholecalciferol. Vitamin D₃ can also be produced by the body when ultraviolet rays from the sun reach the skin.The vitamin D we get from exposure to sun, food or supplements is biologically inert. This practically means that it doesn’t do anything in the body. In order to be activated, it has to undergo two chemical processes, known as hydroxylations. The first takes place in the liver and converts vitamin D to 25-hydroxyvitamin D, or calcidiol. The second hydroxylation is performed in the kidneys and produces the 1,25-dihydroxyvitamin D, or calcitriol. Calcitriol is the form of vitamin D that is physiologically active.

Health benefits of vitamin D

Vitamin D plays an important role in several functions within our body, including:

• Regulating the absorption of calcium and phosphorus.
• Is important for normal muscle function
• Is important for building strong teeth
• Contributes to the normal functioning of the immune system: Vitamin D interacts with cells involved in immune response. Insufficient levels of vitamin D could impair their normal function.

How much vitamin D do you need?

The recommended dietary allowance (RDA)Recommended Dietary Allowance (RDA) is the average daily intake sufficient to meet the nutritional requirements of 97%-98% of healthy individuals. for vitamin D is 15 mcg per day.

Under normal circumstances, about two-thirds of the vitamin D we need can be synthesised by our body following sun exposure. Spending 5-30 minutes in midday sunlight twice a week is considered sufficient. If your access to sunlight is limited or absent, you can use food supplements to get enough vitamin D.

Vitamin D in foods

Overall, few foods naturally contain vitamin D. In some mushrooms, it is present as vitamin D₂. As vitamin D₃ its best sources are fatty fish (salmon, tuna, mackerel), fish liver oils and, to a lesser extent, beef liver, cheese and egg yolks.

Both Vitamin D₂ and vitamin D₃ are considered equivalent. The only difference is observed in doses above the recommended dietary allowance, when vitamin D₂ becomes less potent.

These are the top sources of vitamin D:

* Based on the recommended dietary allowance (RDA) established by EFSA for healthy adults (15 mcg/day)

On food and supplement packaging, vitamin D content can be measured in either micrograms or International Units (IU). 1 IU = 0.025 mcg of vitamin D.

What if you’re not getting enough vitamin D?

Northern latitudes are traditionally associated with a higher risk of vitamin D deficiency due to limited opportunities for sun exposure. However, latitude is not the only factor at play. Although data are not available for all countries and demographic groups, the data that are available already show that Vitamin D deficiency affects people worldwideSource: The Journal of Steroid Biochemistry and Molecular Biology . That includes those residing in countries with year-round sun exposure, like the Middle East. Differences in the levels of vitamin D synthesis can result from factors such as age, extensive skin coverage or little exposure to sunlight.

Typical consequences of vitamin D deficiency are rickets and osteomalacia. These diseases are characterised by softening of the bones and skeletal deformities. Over time, insufficient vitamin D can reduce the absorption of calcium and contribute to osteoporosis.

Groups at highest risk of vitamin D deficiency include:

• Breastfed babies: There is only little vitamin D in breast milk. Although increased vitamin D intake by the mother can improve its content in milk, additional supplements are still advised to meet the infant’s dietary needs.
• The elderly: The skin’s ability to synthesise vitamin D deteriorates with age. An additional risk factor for the elderly is the increased amount of time spent indoors.
• Those with limited sun exposure: This includes people wearing extensive skin coverage and those whose profession or lifestyle limits their exposure to the sun (e.g. mine workers).
• Those with darker skin: Darker skin contains a greater amount of melaninMelanin is the pigment that gives human skin, eyes and hair their colour.. Melanin reduces the skin’s ability to produce vitamin D from sunlight.
• People suffering from health conditions that cause fat malabsorption, like inflammatory bowel disease.
• Obese people: Higher intakes of vitamin D might be required by obese people, due to their higher levels of subcutaneous fatSubcutaneous fat is the layer of fat found under the skin.. Subcutaneous fat affects the release of vitamin D into the blood circulation.

How much vitamin D is too much?

Overconsumption of vitamin D can be harmful to your health. However, a potentially dangerous amount of vitamin D can only ever result from dietary supplement consumption. Neither food, nor sun exposure can lead to a toxic level of vitamin D in the body.

Symptoms of excessive vitamin D consumption include nausea, constipation, appetite and weight loss. Additionally, calcium levels in the blood increase, affecting normal heart rhythm and causing disorientation. Over the long run, vitamin D overconsumption can damage the kidneys.

To stay on the safe side, a tolerable upper intake level (UL) has been established at a maximum of 100 mcg/day for adults. This level is unlikely to have adverse health effects.

Take-aways

The top three facts for you to keep in mind about vitamin D:

• Together with calcium, vitamin D plays a role of skeletal muscle and the normal functioning of the immune system.
• Vitamin D is present in very few foods, including fatty fish like salmon and tuna, as well as fish liver oils. Under normal circumstances, about two-thirds of the vitamin D we need is produced by the skin following sunlight exposure.
• Excessive intake of vitamin D is unlikely to result from food consumption or sun exposure. However, vitamin D supplements exceeding the tolerable upper intake level (UL) can harm your health.

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