Vitamin D for a strong immune system

Vitamin D

The UK authorities new recommendation on vitamin D is an intake of 10mcg (400IU) for those over 1 year of age, which in many cases means supplementing as vitamin D and sun exposure are closely linked. But that  might not be high enough…. 

What is Vitamin D?

Vitamin D is a hormone mainly produced by our bodies when we expose our skin to sunlight. At latitudes of around 52 degreees and higher (London’s latitude is 51.55 degrees) people do not produce sufficient vitamin D in the winter and therefore rely on stores from the summer months and, to a lesser extent, dietary sources.

However, levels of vitamin D acquired during the summer may be too low for people with darker skin, those spending a substantial part of the day indoors, especially the elderly and those using high factor sunscreen or covering up their skin when outdoors, including young babies.

The length of time needed to produce sufficient vitamin D has not been established but several UK Health organisations, advise that regularly going outside in the summer for a few minutes around the middle of the day without sunscreen should be enough, although factors like skin tone, overcast and polluted skies and clothing may impact vitamin D production.

Important note: The amount of time you choose to expose your skin to sunlight without sunscreen should always be less than that needed to redden or burn the skin as recommended by Cancer Research UK. At any other times, it is recommended that sunscreen is used. 

Vitamin D and health

Bone health

Vitamin D increases calcium absorption in the gut and reduces urinary calcium loss by increasing re-absorption in the kidneys. Calcium deficiency may lead to rickets, osteomalacia, osteoporosis, tooth decay, brittle nails, numbness and tingling in the hands, muscle cramps and insomnia.


Vitamin D is also important to maintain a healthy immune system and its deficiency has been associated with autoimmune conditions and higher risk of infection.


Sunlight exposure resulting in increased levels of vitamin D are associated with reduced occurrence, and reduced mortality, in certain cancers including skin, prostate, breast, colon, ovary, kidney and bladder as levels of vitamin D may be an important modulator of cancer progression.


Research studies show that vitamin D may help increase cell sensitivity to insulin, which in turn helps regulate blood sugar levels. Additionally, vitamin D is a powerful antioxidant that can help mitigate the harmful oxidative effects associated with high levels of blood glucose in type 2 diabetics.


Vitamin D status can also affect pregnancy outcome and research has linked vitamin D deficiency to gestational diabetes.  


Vitamin D has also been linked to mental health and deficiency could be a causing factor in depression although more research is needed in this area

Dietary sources of Vitamin D

Vitamin D is found in some foods such as oily fish (tuna, salmon, sardines, mackerel) with 5-10μg/100g, fortified cereals and yogurt and to a lesser extent in egg yolk (5μg/100g) and red meat (1μg/100g). Food sources alone do not provide sufficient vitamin D, we still need exposure to sunlight or supplementation.

Vitamin D supplementation

The new advice from the UK Public Health Authority is that adults and children over the age of one should consider taking a daily supplement containing 10mcg (400IU) of vitamin D, particularly during autumn and winter.

This dose, however, is low in comparison to the Vitamin D Council recommendation of 1,000IU for infants, 1,000IU per 25kg body weight for children and 5,000IU for adults.

Vitamin D is fat soluble which means that your body can’t excrete it quite so easily although the European Food Safety Agency (EFSA) have established vitamin D upper limit supplementation at 100 μg/d (4000 IU) for adults and children aged 11-17y, 50 μg/d (2000 IU) for children aged 1-10y and 25 μg/d (1000 IU) for infants.

Vitamin D may be toxic in large doses, so if you think you might be vitamin D deficient please contact your GP or nutrition advisor before taking any supplements. Symptoms of vitamin D toxicity include kidney disorders and renal insufficiency as well as gastrointestinal disorders and high blood pressure. 

Note that babies being fed on formula will get some vitamin D from their milk, so take that into account if supplementing.

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