Understanding Vitamin D and Its Importance

Vitamin D sunshine

Vitamin D is an essential nutrient that is involved in many important functions in the body, including cell growth, neuromuscular and immune function, and reducing inflammation. It is unique among vitamins in that it can be made in the skin from exposure to sunlight or obtained through dietary sources. (1,2)

The Role of Sunlight in Vitamin D Production

Sunlight is a primary source of vitamin D. When the skin is exposed to sunlight, a type of cholesterol in the skin is converted into vitamin D. However, the amount of vitamin D produced depends on various factors, including the time of day, season, and latitude.

  • It is recommended to spend about 20 minutes per day in the sun, avoiding the time when the sun is strongest, to ensure adequate vitamin D absorption.
  • For daily walk inspiration, read here.

Why Many People Are Deficient in Vitamin D

From October until the end of March in the UK, the sun’s strength is not sufficient to produce vitamin D, and unfortunately, most of us cannot obtain enough vitamin D from our diet alone. This puts us at risk of vitamin D deficiency.

  • A supplement can help maintain adequate levels of vitamin D during the colder months.
  • In the summer, we usually use high-factor sunscreen, which blocks UVB rays that stimulate vitamin D production in the skin.
  • People with dark skin require more sunlight exposure to stimulate vitamin D production due to the melanin pigment, which inhibits UV light from penetrating far enough into the skin for vitamin D synthesis.

Supplementing with Vitamin D3

For individuals who are deficient in vitamin D, a supplement of vitamin D3 is recommended. Vitamin D3 is the most effective form of vitamin D, and it is the same form that is produced in the skin.

  • The amount of vitamin D needed varies depending on the individual and their level of deficiency.
  • It is important to consult a doctor before taking vitamin D supplements to ensure proper dosage and avoid any potential harmful effects.

Vitamin D2 and Vitamin D3: Differences and Sources

Vitamin D2 is derived from the UV irradiation of the yeast sterol (ergosterol) and is naturally present in sun-exposed mushrooms. On the other hand, vitamin D3 is synthesized in our bodies when the skin is exposed to UVB rays from the sun.

  • Fish such as salmon, mackerel, and herring are rich in vitamin D3.
  • Due to the lower cost of production, vitamin D2 is more commonly used in fortified foods.

Vitamin D in the Body

Vitamin D is an essential nutrient that plays a crucial role in the absorption of calcium and phosphorus in the body. However, the vitamin D that comes from the skin or diet is biologically inert and requires transformations in the liver and kidneys to form the biologically active form of vitamin D.

  • Without sufficient vitamin D, only a small fraction of dietary calcium and phosphorus are absorbed by the body.
  • In contrast, vitamin D sufficiency can enhance calcium and phosphorus absorption by 30–40% and 80%, respectively. (3)

Deficiency Symptoms

Vitamin D deficiency can lead to various symptoms such as lack of energy and fatigue, headaches, poor immune system, muscle aches, and depression.

Food Sources

Very few foods in nature contain vitamin D. Vitamin D in these foods is primarily in the form of vitamin D3.

  • Fatty fish, such as salmon, tuna, and mackerel, and fish liver oils are among the best sources of vitamin D.
  • Small amounts of vitamin D are also found in beef liver, cheese, and egg yolks.
  • Some mushrooms provide vitamin D2 in variable amounts.
  • Additionally, mushrooms can be exposed to ultraviolet light under controlled conditions to enhance their vitamin D2 content.
  • However, fortified foods represent the primary dietary sources of vitamin D in the modern diet, as very few foods naturally contain significant amounts of vitamin D.


While it can be challenging to obtain sufficient vitamin D from natural food sources alone, many people turn to supplements to meet their daily needs.

  • The amount of vitamin D needed varies according to each person.
  • According to the National Health Service (NHS), 10mcg/400 IU of vitamin D3 a day is sufficient for most people for maintenance. (5)
  • It’s crucial to consult a doctor before taking vitamin D supplements to ensure that the recommended intake is appropriate for your individual needs.

In conclusion, vitamin D is a vital nutrient that plays a significant role in maintaining healthy bones, teeth, and muscles, as well as regulating calcium and phosphate levels in the body. While it can be challenging to obtain sufficient vitamin D from natural food sources alone, sunlight exposure, fortified foods, and supplements can help individuals meet their daily needs. It is essential to maintain adequate levels of vitamin D to prevent various deficiency symptoms and maintain good health. Consultation with a doctor is recommended before taking vitamin D supplements to determine the appropriate dosage and avoid any potential harmful effects.


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