Vitamin D

Vitamin D, also known as the “sunshine vitamin,” is a fat-soluble vitamin that plays a crucial role in maintaining bone health, immune function, and other physiological processes. There are two main forms of vitamin D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is synthesized in the skin upon exposure to sunlight, while both forms can be obtained through diet and supplements.


The history of vitamin D dates back to the early 20th century when researchers were trying to find a cure for rickets, a bone disease in children characterised by weak, soft bones and skeletal deformities. The disease was prevalent in industrialised cities, where children had limited exposure to sunlight.

In 1918, Sir Edward Mellanby, an English physician, conducted experiments on dogs and demonstrated that rickets could be cured by including cod liver oil in their diet. In 1922, American researcher Elmer McCollum discovered that the “antirachitic” substance in cod liver oil was not vitamin A, as initially thought, but a new vitamin, which he named vitamin D.

In the 1930s, the process of irradiating certain foods with ultraviolet light to increase their vitamin D content began. This led to the fortification of milk and other dairy products, which significantly reduced the incidence of rickets in children.

Further research into vitamin D revealed its essential role in calcium and phosphorus metabolism, as well as its impact on immune function and overall health. The discovery of vitamin D receptors in various tissues and organs highlights its diverse functions throughout the body.

Functions Of Vitamin D

Vitamin D plays a crucial role in various physiological processes in the body. Some of the primary functions of vitamin D include:

  • Bone health: Vitamin D is essential for maintaining healthy bones and teeth. It helps regulate the absorption of calcium and phosphorus in the body, which are critical minerals for bone strength and density.
  • Calcium homeostasis: Vitamin D plays a vital role in maintaining the balance of calcium in the body. It helps increase the absorption of calcium from the intestines and works with parathyroid hormone (PTH) to regulate calcium levels in the blood.
  • Immune function: Vitamin D is involved in the regulation of the immune system, modulating both innate and adaptive immune responses. It helps in the activation and proper functioning of immune cells, including T cells and macrophages.
  • Anti-inflammatory properties: Vitamin D has been shown to exhibit anti-inflammatory effects, reducing inflammation in the body, and potentially lowering the risk of chronic inflammatory diseases.
  • Cell growth and differentiation: Vitamin D is involved in the regulation of cell growth, proliferation, and differentiation. It plays a role in maintaining the health of various tissues and organs, including skin, hair follicles, and the lining of the digestive tract.
  • Neuromuscular function: Vitamin D is essential for proper neuromuscular functioning, supporting muscle strength, and coordination.
  • Mood regulation: There is evidence suggesting that vitamin D may play a role in mood regulation and the prevention of depression, although further research is needed to confirm these findings.
  • Heart health: Some studies have suggested that adequate vitamin D levels may help maintain cardiovascular health, although more research is needed to establish a clear link between vitamin D and heart health.

Given the diverse functions of vitamin D, it is important to maintain adequate levels through a combination of sun exposure, diet, and supplementation, if necessary, to support overall health and well-being.

Good Sources Of Vitamin D

Vitamin D is unique in that the body can produce it when the skin is exposed to sunlight. However, it can also be obtained through certain foods and supplements. Good sources of vitamin D include:

  • Sunlight: Ultraviolet B (UVB) radiation from the sun stimulates the production of vitamin D3 in the skin. However, factors like geography, time of year, skin pigmentation, and sunscreen use can affect the amount of vitamin D produced.
  • Fatty fish: Fish such as salmon, mackerel, sardines, and trout are good sources of vitamin D3.
  • Cod liver oil: This oil is one of the richest natural sources of vitamin D. However, it is also high in vitamin A, which can be toxic in large amounts, so it’s essential to use it in moderation.
  • Fortified foods: Some foods are fortified with vitamin D to help people meet their dietary needs. These may include milk, orange juice, yogurt, and breakfast cereals.
  • Egg yolks: Eggs contain small amounts of vitamin D, primarily in the yolk.
  • Cheese: Some types of cheese, like Swiss and cheddar, contain small amounts of vitamin D.
  • Beef liver: Though not a popular food choice for many, beef liver is a good source of vitamin D.
  • Mushrooms: Some types of mushrooms, particularly those exposed to UV light, can provide vitamin D2. However, the amount of vitamin D in mushrooms is variable and typically lower than animal-based sources.

Since there are limited natural food sources of vitamin D, and factors like limited sun exposure can affect its production in the body, many people may need to consider taking vitamin D supplements to maintain adequate levels. It is essential to consult with a healthcare professional before starting any supplementation to determine the appropriate dosage based on individual needs and health conditions.

How Much Vitamin D Do We Need?

The National Institutes of Health (NIH) provides reliable information on nutrient recommendations. According to the NIH, the Recommended Dietary Allowance (RDA) for vitamin D varies based on age, sex, and life stage. Here are the general guidelines:

  • Infants (0-12 months)*: 400 International Units (IU) or 10 micrograms (mcg) per day
  • Children (1-18 years): 600 IU or 15 mcg per day
  • Adults (19-70 years): 600 IU or 15 mcg per day
  • Adults (71 years and older): 800 IU or 20 mcg per day
  • Pregnant and breastfeeding women: 600 IU or 15 mcg per day

*For infants, the values provided are Adequate Intakes (AI) rather than DRIs, as there is not enough data to establish DRIs for this age group.

These values are general guidelines, and individual needs may vary depending on factors such as overall health, lifestyle, and sun exposure. It is essential to consume adequate amounts of vitamin D through a combination of sun exposure, diet, and supplementation if necessary. If you are concerned about your vitamin D intake, consult with a healthcare professional for personalised advice.

What Are The Signs Of Vitamin D Deficiency?

Vitamin D deficiency can lead to various symptoms and health issues. Some of the signs and symptoms of vitamin D deficiency include:

  • Bone pain and weakness: Vitamin D is essential for calcium absorption and maintaining strong bones. A deficiency can lead to bone pain, weakness, and an increased risk of fractures.
  • Muscle weakness and pain: Low vitamin D levels can cause muscle weakness, pain, and overall discomfort, particularly in the legs, pelvis, and lower back.
  • Fatigue: Vitamin D deficiency is often associated with chronic fatigue and low energy levels.
  • Frequent infections: Vitamin D plays a crucial role in immune function. A deficiency can result in a weakened immune system, making you more susceptible to infections and illnesses.
  • Depression or mood changes: Some studies have linked vitamin D deficiency to depression and mood disorders, although more research is needed to confirm these findings.
  • Slow wound healing: Inadequate levels of vitamin D can impair the body’s ability to heal wounds and fight infections.
  • Hair loss: Severe vitamin D deficiency has been associated with hair loss, particularly in conditions like alopecia areata, an autoimmune disease that results in hair loss.
  • Softening or weakening of bones: In children, severe vitamin D deficiency can cause rickets, a condition characterised by soft, weak bones and skeletal deformities. In adults, it can lead to osteomalacia, which results in bone pain and increased susceptibility to fractures.

If you suspect you have a vitamin D deficiency, it is important to consult with a healthcare professional for proper diagnosis and treatment. Adequate sun exposure, a balanced diet, and supplementation when necessary, can help maintain optimal vitamin D levels and support overall health.

What Happens If I Take Too Much Vitamin D?

Vitamin D is a fat-soluble vitamin, which means that excessive amounts can be stored in the body and potentially lead to toxicity. Taking too much vitamin D, particularly in supplement form, can cause a range of symptoms and health issues. Some of the consequences of vitamin D toxicity include:

  • Hypercalcemia: High levels of vitamin D can lead to an increase in calcium levels in the blood (hypercalcemia), which can cause symptoms such as nausea, vomiting, constipation, abdominal pain, and loss of appetite.
  • Kidney stones: Elevated calcium levels due to vitamin D toxicity can increase the risk of developing kidney stones, particularly calcium-based stones.
  • Kidney damage: Excessive vitamin D intake can cause kidney damage over time due to the build-up of calcium deposits in the kidneys and other organs.
  • Heart problems: Hypercalcemia resulting from vitamin D toxicity can lead to an irregular heartbeat, high blood pressure, and other cardiovascular issues.
  • Bone pain and weakness: Paradoxically, too much vitamin D can cause bone pain and weakness, as well as increase the risk of fractures.
  • Neurological symptoms: Vitamin D toxicity may cause confusion, disorientation, dizziness, and in severe cases, seizures, or coma.

It is important to remember that vitamin D toxicity is usually caused by excessive supplementation rather than dietary sources or sun exposure. To avoid toxicity, adhere to the Recommended Dietary Allowance (RDA) for vitamin D and consult with a healthcare professional before taking supplements, especially if you are considering doses higher than the RDA.