Vitamin D

This article is written by Beyda Beteri ANutr.

Vitamin D (also known as “calciferol”) is a fat-soluble vitamin found naturally in certain foods, as a dietary supplement, and produced from ultraviolet (UV) rays when exposed to sunlight. The fat-soluble vitamin means that Vitamin D needs the presence of fat in the gut to be well absorbed.

What does Vitamin D do?

Vitamin D is needed for cell growth, bone health, normal neuromuscular and immune function, prevention of inflammation and glucose metabolism.

Vitamin D supports the absorption of calcium in the gut and thus supports bone health, reducing the risk of diseases in which bones become brittle and weak, such as osteoporosis in adults and rickets in children.

In addition, Vitamin D maintains an adequate concentration of serum phosphate, which ensures normal bone mineralization and prevents muscle contractions, cramps and spasms [1,2].

Furthermore, Vitamin D acts as a barrier on skin and mucosal surfaces, destroying bacteria and viruses, and protecting the body against infections by stimulating the cellular immune response [1,3].

Vitamin D2 and D3: What is the difference?

Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are the two main forms of vitamin D. Vitamin D2 is obtained through diet. D3 is produced in the skin by UVB radiation when bare skin is exposed to sunlight. D3 can also be obtained in very small amounts from certain animal foods [3].

How much vitamin D do I need?

From the age of 1, the daily need for vitamin D is 10 (400 IU) micrograms. This also applies to pregnant women, breastfeeding women and individuals with the risk of vitamin D deficiency [7].

From approximately the beginning of April to the end of September, most people should be able to meet their vitamin D needs from sunlight. It is recommended to take vitamin D supplementation from the end of September to the beginning of April including pregnant and breastfeeding women.

The Ministry of Health and Social Care also recommends that people who are not outdoors and not regularly exposed to sunlight take a daily vitamin D supplement throughout the year. The Tolerable Upper Intake Level for Vitamin D supplementation in adults is 100 micrograms (4000 IU) [2,7].

Sources of Vitamin D

“People should aim to meet their nutritional needs primarily from food, and for vitamin D, if possible, from the sun and food. Supplements should be supported with a healthy diet.’’

Vitamin D from the sun:

Vitamin D3 is produced in the skin by UVB radiation when bare skin is exposed to sunlight [3].  

Vitamin D-rich foods:

Besides sunlight, you can also get vitamin D by consuming plenty of vitamin D-rich foods. Also, “vitamin D-fortified” food options have been increasing in recent years.

Herring, grilled119g19.2 micrograms
Salmon, grilled or canned170g13.3-13.6 micrograms
Kipper fillet, grilled130g 13.1 micrograms
Mackerel, smoked150g12.3 micrograms
Malted hot drinks, fortified powder 25g – 1 mug4.6 micrograms
Eggs, scrambled or boiled2 eggs3.3 micrograms
Soya milk, fortified200 ml1.6 micrograms
Cornflakes and bran flakes, fortified30g1.4 micrograms
Margarine5g- 1 teaspoon0.4 microgram
Pork sausages, grilled or fried40g0.4 micrograms
Table1. Vitamin D content of selected foods per average portion [4].

UV-treated mushroom powder dietary supplement:

It has also been approved by the Food and Drug Administration (FDA) that UV-treated mushroom powder can be used as a dietary supplement source of vitamin D2 [2]. The New Foods and Food Allergens (NDA) also provided an opinion on the safety of Vitamin D2 mushroom powder supplementation at the European Food Safety Authority (EFSA) Panel on Nutrition. The panel concluded that the use of mushroom powder containing vitamin D2 in the range of 125–375μg/g is safe under the recommended conditions of use [5].

Vitamin D supplementation:

As mentioned, it is recommended to take a dietary supplement of at least 10 micrograms (400IU) of vitamin D daily from October to March. Vitamin D supplements are available in tablet, capsule and spray forms, and can be bought from pharmacies and supermarkets. Please do not take more than 100 micrograms (4,000 IU) of vitamin D per day as it can be harmful, causing toxicity.

Effects of Vitamin D on various health conditions

  • Heart diseases

Vitamin D helps regulate the renin-angiotensin-aldosterone system (RAAS), a hormone system that regulates blood pressure. Therefore, vitamin D deficiency is associated with vascular dysfunction, arterial stiffness and hyperlipidemia, which increases the risk of heart disease and cardiovascular disease [2].

  • Depression

Vitamin D receptors are located in neurons and glial cells of the brain thought to be involved in the pathophysiology of depression. Some systematic reviews and meta-analyses have found associations between low vitamin D levels (25(OH)D) and depression. But clinical studies have not found an association. Therefore, more clinical studies are needed [2].

  • Cancer

Some observational studies and systematic reviews have shown that increased levels of vitamin D (serum 25(OH)D) reduce cancer risk and cancer death rates [8,9].

  • Diabetes

Vitamin D stimulates insulin secretion through vitamin D receptors in the pancreas and reduces peripheral insulin resistance(impaired glucose uptake)through vitamin D receptors in the muscles and liver. Therefore, vitamin D is involved in the pathophysiology of type 2 diabetes through its effects on glucose metabolism [10].


  7. Vitamin D – NHS (

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