Guide to vitamin D

Vitamin D, the so-called sunshine vitamin, is found in small amounts in food, but the majority (90 per cent) is made by the body on exposure to UVB sunlight. It's produced in the skin and is vital for healthy bones, teeth, and muscles, and is increasingly believed to play a role in immune function.

The big problem in the UK is that we can only make vitamin D when the sun’s UV index is greater than three, and our sunlight just isn’t that strong in the autumn and winter. The National Diet and Nutrition Survey published in 2016 found one in five people aged 19 to 64, one in six aged 65 and over, and children aged 11 to 18 had low vitamin D status throughout the year. Supplements are regarded as a useful top-up.

Dr Sarah Brewer says: 'Public Health England recommends that everyone over the age of one year should take a daily supplement providing 10mcg vitamin D during autumn and winter. This is very much a minimum to prevent deficiency diseases. Choose a vitamin D3 (cholecalciferol) supplement which is the same form made by the body on exposure to sunlight, and is more effective in maintaining blood vitamin D levels than the vitamin D2 (ergocalciferol) form, which comes from plant sources.’

What does vitamin D do?

Vitamin D regulates levels of calcium and phosphorous, which are needed for healthy bones and teeth. It also activates macrophages; hunter-killer white blood cells in the body’s immune defence system.

What’s the difference between vitamin D2 and D3?

Vitamin D2 is made synthetically from fungus and plant matter. Vitamin D3 (also known as cholecalciferol) is the same type as made by the body via exposure to sunlight. Vitamin D3 is more effective at maintaining blood levels than vitamin D2.

Bone health

Vitamin D deficiency can lead to bone deformities including rickets in children and joint pain and tenderness, muscle weakness and pain in the spine, ribs, shoulder or pelvis in adults, due to a condition called osteomalacia (soft bones).


Vitamin D may also play a role in immunity. A 2016 study found older people in long term care given high doses of vitamin D3 monthly were 40 per cent less likely to suffer from acute respiratory illnesses.

A review of studies in 2016 concluded that people with mild to moderate asthma who took vitamin D3 supplements had fewer severe attacks overall.

A study published in 2017 in the British Medical Journal found daily or weekly vitamin D supplements halved the risk of respiratory infections in people with the lowest levels of the vitamin. In people who had higher vitamin D levels, supplements cut their risk of an infection by 10 per cent.

Muscle strength

Research suggests many athletes are vitamin D deficient; a 2016 survey of elite National Basketball Association (NBA) basketball players in the United States, found 79.3 per cent were either vitamin D deficient or insufficient.

Impaired muscle function, reduced immune function, poor bone health and cardiovascular conditions have all been associated with vitamin D deficient athletes. All these factors can affect performance, so making sure you have a daily source of vitamin D is essential.

Getting vitamin D from your diet

Vitamin D is found in many foods, including: egg yolks; oily fish (salmon, mackerel, herring and sardines); dairy products and fortified margarines; and meat (liver and kidney). Sunshine, not food, is the main source though.


The UK’s Expert Group on Vitamins and Minerals advise a level of 25mcg a day would not be expected to cause adverse effects in the general population.

Excessive doses of vitamin D supplements can lead to side effects associated with high calcium levels, such as: kidney stones; hypercalcaemia (where calcium is deposited in soft tissue); demineralisation of bones; headaches; and weakness.

It’s not possible to overdose on vitamin D from the sun, but prolonged sun exposure without suncream is dangerous because of the risk of skin cancer.

Correct dosage

Public Health England (PHE) now recommends all adults and children aged one and over need 10mcg of vitamin D a day and advises some people may want to take a supplement, particularly during autumn and winter.

PHE also recommend those aged over 65; pregnant or breastfeeding women; people with inadequate exposure to sunlight (including those who cover their bodies with clothing for cultural reasons or live in residential care homes); and people of African, Afro-Caribbean or south Asian origin may want to take a supplement all year round.

The safe daily intake recommended for infants (under one) is 8.5mcg to 10mcg, but those drinking 500ml or more of infant formula do not need supplements as formula milk is fortified with vitamin D.

Public Health England recommends that everyone over the age of one year should take a daily supplement providing 10mcg vitamin D during autumn and winter. This is very much a minimum to prevent deficiency diseases.

Dr Sarah Brewer


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