Comprehensive Guide To Vitamin D

Vitamin D is perhaps the most well-known vitamin because of our incredible ability to produce vitamin D upon sun exposure to the skin, hence otherwise known as the 'sunshine vitamin'. But vitamin D is not actually a vitamin at all, rather a prohormone.

During Covid-19, while we are all indoors, it is vital to ensure you are getting enough vitamin D from your diet and adequate sun exposure at a safe distance from other people.

What Is Vitamin D?

Vitamin D, also known as calciferol collectively, is a group of five forms of fat-soluble vitamins, the most important of which are vitamin D2 (ergocalciferol), derived from plants and vitamin D3 (cholecalciferol), derived from animals. We can produce some vitamin D3 in our skin from a reaction between 7-dehydrocholesterol and UVB ultra-violet sunlight. However, this only occurs when the UV index is greater than 3, which, in the UK is an unlikely phenomenon. Jokes aside, this can be achieved during the summer and spring. But during autumn and winter, we cannot produce enough vitamin D to meet our needs so our vitamin D levels tend to fall.

After vitamin D is consumed, or absorbed through the skin, it enters the blood circulation and is then converted into the active hormone, calcitriol, within the kidneys. Some of the conversion also occurs within the prostate, colon, skin and bone cells.

Calcitriol has several important functions within the body including:

• Regulates absorption of calcium and phosphate within the small intestines

• Promotes reabsorption of calcium in the kidneys, meaning less is lost in the urine

• Reduces secretion of the parathyroid hormone (reduces the release of calcium from the bones)

• Helps balance the production and breakdown of collagen and elastin

• Stimulates new cartilage production

• Bolsters white blood cells

• Important for brain health

• Important for cardiovascular health

To balance vitamin D production and the development of skin cancer, it is recommended to get 10 to 15 minutes of sun exposure two to three times a week without sunscreen. Long exposure to the sun does not provide any benefit as the vitamin D production deteriorates rapidly from the excess UV radiation.

Lack of vitamin D reduces bone mineralization. This can lead to developing rickets in children and osteomalacia in adults. When vitamin D supply is low, less calcium is absorbed, therefore calcium must be leached from the bones to maintain adequate levels. Four out of five people with hip fractures have been associated with vitamin D deficiency. Other conditions associated with vitamin D deficiency include muscle weakness, poor growth, constipation, increased susceptibility to infections, irritability, bone deformity and deafness.

History Of Vitamin D

In 1840, a Polish physician named Sniadecki discovered that rickets occurred in children living in industrial areas of Warsaw, but the children outside, living in the country did not have cases of rickets. He pointed to the lack of exposure to sunlight in the narrow, crowded industrialised city and pollution from burning coal and wood, caused rickets. The people did not take the thought seriously as at that time the idea of the sun having any benefit upon the skeleton.

As industrialisation increased by the end of the 19th-century rickets was estimated to affect over 90% of children living in polluted urban areas in Europe. Similarly, the same happened in Boston and New York City in the late 1800s, until 1900 over 80% of children were reportedly affected by rickets.

In 1918, a British man named Sir Edward Mellanby discovered that beagles housed indoors only and fed a diet of oatmeal, developed rickets but once cod liver oil was added to the food the disease subsided. In 1921 he noted, "The action of fats in rickets is due to a vitamin or accessory food factor which they contain, probably identical with the fat-soluble vitamin".

Various other experiments in the 1920s followed this in which pieces of rat skin were exposed to UV radiation or rat food was UV irradiated. Both treated rickets.

Sir Edward Mellanby, 1943

Benefits Of Vitamin D


Vitamin D is important for those with osteoarthritis. Studies have found up to a 400% higher risk of osteoarthritis progression in those with low vitamin D levels compared to those with high levels.


Vitamin D is vital for calcium deposition in bone and maintaining bone density. A meta-analysis from 29 clinical studies involving over 60,000 senior individuals suggests that calcium supplements reduce the risk of bone fracture. This is boosted when calcium is supplemented at 1.2g, along with 20mcg of vitamin D or more.

Doses higher than 10mcg of vitamin D per day could possibly reduce non-vertebral fractures by at least 20%. The lead observer commented that everyone over the age of 65 should take 20mcg of vitamin D3 each day for bone health benefits.


Calciferol is believed to bind to receptors in cancer cells and improve gene expression and reduce abnormal cell division. By improving signal responses between cells it has the ability to stop prolific cancer growth.

Vitamin D has been shown to reduce proliferation and growth of cancer cells in over 25,000 laboratory studies and may reduce the risk of certain cancers, especially prostate, colon and breast.

Genetic predisposition of vitamin D receptors may have an impact on the likelihood of developing cancer.

Heart Disease

Vitamin D seems to be just as important for cardiovascular health as it is for healthy bones. It is essential for calcium metabolisation and may reduce the amount of calcium deposited in the artery walls as part of the hardening and furring process.

It may also help control blood pressure through the hormone system renin-angiotensin-aldosterone, or possibly through the effects on the parathyroid hormone. In a study on 15,000 American adults those with the lowest vitamin D levels were 30% more likely to have high blood pressure and nearly 100% more likely to have diabetes.

Other studies suggest low vitamin D intake is a risk factor for heart attack, heart failure and Type 1 and Type 2 diabetes.

Common Cold

Like vitamin C, vitamin D also has an effect on the prevention of common colds. A study on 19,000 adults and adolescents found that those with the lowest vitamin D intake were 40% more likely to develop a cold.


Children with lower levels of vitamin D are more likely to develop asthma and a higher chance of having an asthma attack.


Vitamin D may reduce the damage to the teeth from excess fluoride (fluorosis).


Vitamin D receptors are distributed throughout the brain, which appears to be involved in learning, memory snd mood. It may possibly protect against dementia, Parkinson's disease and multiple sclerosis. Low levels of vitamin D have been associated with the development of chronic pain.


Calciferol is important for skin health and may also be an effective treatment for some forms of psoriasis.

Vitamin D Deficiency

If you do not get much sun often, are vegan or don't eat fish then you may be at risk of vitamin D deficiency. This can be resolved by taking vitamin D supplements or multi-vitamins. Symptoms of vitamin D deficiency include:

• Susceptible to infections

• Fatigue

• Bone pain

• Depression

• Slowed wound healing

• Bone loss

• Hair loss

• Muscle pain

More severe symptoms of vitamin D deficiency include:

• Higher risk of death from cardiovascular disease

• Brain impairment in senior individuals

• Asthma development and severe asthma attacks

• Cancer

Vitamin D Dosage

The upper safe level of long-term use of vitamin D supplementation recommended by the Europian Food Safety Authority is 50mcg. Note: 5mcg is equivalent to 200IU (international units.)

0-12 months: 10mcg

1-13 years: 15mcg

14-18 years: 15mcg

19-50 years: 15mcg

51-70 years: 15mcg

70+ years: 20mcg

Pregnancy: 15mcg

Breast-feeding: 15mcg

Vitamin D Overdose

Toxic effects occur at doses exceeding 500mcg (0.5mg) per day. These symptoms include:

• Headache

• Loss of appetite

• Nausea

• Vomiting

• Diarrhoea

• Constipation

• Palpitations

• Fatigue

Sources Of Vitamin D

• Sun exposure

• Oily fish

• Red meat

• Liver

• Egg yolk

• Mushrooms

• Whole milk

• Fortified foods

Should You Supplement Vitamin D?

A healthy, balanced diet along with regular exposure to the sun will provide all the vitamin D you need. If you are vegan, you should supplement vitamin D. Small dose supplements may be beneficial during autumn and winter otherwise, it is likely unnecessary to supplement vitamin D.

Supplementing during Covid-19 may be beneficial as we are encouraged to stay inside and social distance from others.