Vitamin D

How much do you need daily?

Adults need 10 micrograms (*400 IU) of vitamin D a day.

In spring and summer, most people in the UK get enough vitamin D through the action of sunlight on the skin, but in the winter months a supplement is required.  

*Supplements may be marked in International Units (IU), rather than micrograms. The conversion is 40 IU to one microgram, so 10 micrograms is equal to 400 IU.

Official advice

Previously, the government only recommended daily amounts for babies, pregnant women and the elderly, assuming most people got enough vitamin D from sunshine. However, on realising how low vitamin D levels are in the population, in 2016 Public Health England changed their advice and now say that during autumn and winter, everyone in the UK needs a dietary source of vitamin D. It is hard to get the daily amount needed from food, so for most people, this means taking a supplement.

Are we getting enough?

The 2014 National Diet and Nutrition Survey (NDNS) found that nearly a quarter of adults and one in five children had deficient levels of vitamin D over the whole year, increasing to 40 per cent in winter. In Scotland it was even worse with over half of all adults being deficient in winter, while a staggering 75 per cent of a group of South Asian women living in the South of England were deficient.

In 2016 the NDNS found that around a fifth of adults had low blood levels of vitamin D. In 2018, they found continued evidence of widespread vitamin D deficiency. For children, the situation was even worse, now affecting one in four over the whole year (one in five in 2014).  In the UK, the average daily intake from a ‘normal’ diet is just 2-4 micrograms of vitamin D. Most people don’t get enough from their diet and need more sunshine or a supplement.

Why do we need it?

Vitamin D is necessary for the regulation of calcium levels in the blood and is needed for healthy bones as it helps your body absorb calcium. Vitamin D also regulates phosphate levels. These nutrients are important to keep bones, teeth and muscles healthy. 

It is known as the ‘sunshine vitamin’ because we make vitamin D in our skin in response to exposure to sunlight containing ultraviolet B rays or UVB radiation. In the UK, from around late March or early April to the end of September, we get most of our vitamin D from sunlight exposure. On a sunny day, you can make all the vitamin D you need by exposing your face, arms and legs for five to 30 minutes twice a week. The weaker the sunlight, or the darker your skin, the more exposure you need. Sunscreen blocks vitamin D synthesis, as does glass, and sunbeds are not recommended as alongside UVB, sunbeds emit UVA which can cause skin cancer and does not contribute to vitamin D production. 

There are two types of vitamin D, both can be used by the body, but it's advisable to check the source. Vitamin D2 (ergocalciferol) is always vegan but vitamin D3 (cholecalciferol) can be of animal origin. Most of the vitamin D3 used in supplements and to fortified foods is produced industrially by the ultraviolet irradiation of a substance extracted from lanolin in sheep's wool. It is not suitable for vegans. However, some D3 is now produced from mushrooms and lichen – this is suitable for vegans.

Some vegan foods are fortified with vitamin D2 and labelled so but if not specified, especially on cereal products, the vitamin D tends to be of animal origin. If you choose to supplement your diet, there are quality and affordable vegan supplements made with vitamin D2, or D3 from mushrooms or algae (this is recommended if you need a higher dose). The algae these supplements are made of are not common food ingredients so cannot be recommended as a food source.

Avoid taking too much

Taking too many vitamin D supplements can be harmful as it may cause your body to absorb more calcium than it needs. High calcium levels in the blood (hypercalcaemia) can weaken your bones and damage the kidneys and heart. Government guidelines warn not to take more than 100 micrograms of vitamin D a day as it could be harmful. This applies to adults, including pregnant and breastfeeding women and the elderly and children aged 11-17 years. Children aged 1-10 years shouldn't have more than 50 micrograms a day and infants under 12 months shouldn't have more than 25 micrograms a day.

Do I need a supplement?

Yes, depending on your lifestyle – either over the winter months only (October-March) or throughout the year. Please see the explanation above. When choosing a supplement, 10 micrograms (400 IU) per day is enough and you shouldn’t go above 25 micrograms (1,000 IU).

Overall, 60-70 per cent of the UK population is thought to have low vitamin D levels. Some studies suggest vegans may consume less vitamin D than meat, egg and fish-eaters but this doesn’t seem to make much difference when such a large proportion of the population is deficient, regardless of what they eat. Vitamin D deficiency, it seems, has far more to do with lack of sunshine than diet. The fact is – we all need supplements if we don’t get enough sunshine.

The best plant sources

The best plant sources include vitamin D-fortified plant-based milks, vegetable margarines and breakfast cereals (if labelled suitable for vegans) and vitamin D mushrooms (exposed to sunlight for long enough so vitamin D production is triggered).  

Just like us mushrooms make vitamin D when exposed to sunlight. Most mushrooms you buy don’t have any vitamin D because they’re grown in the dark but some suppliers have started exposing their mushrooms to UV light to produce ‘vitamin D mushrooms’. Analysis shows that vitamin D mushrooms from one supermarket contained 4.07 to 9.37 micrograms of vitamin D per 100 grams. Another supermarket said that a 100 gram serving of their mushrooms contains at least 10 micrograms of vitamin D. 100 grams is equal to approximately: 14 button mushrooms, 4-5 chestnut mushrooms or 1-2 Portobello mushrooms.

Between 1940 and 2013, margarine in the UK had to be fortified and most still is, but on a voluntary basis – as are other foods such as breakfast cereals and some plant-based milk alternatives.  

Vitamin D is found in fatty fish, liver and egg yolks – but only if the chickens have been fed vitamin D. However, all these foods are non-vegan and contain cholesterol, saturated fat and other undesirable substances.

Signs of deficiency

muscle weakness, bone tenderness or pain in the spine, shoulder, ribs or pelvis; vitamin D deficiency in children can lead to rickets – skeletal deformities, anaemia and susceptibility to respiratory infections.