Vitamin D – Don’t be D for deficient

A to Z of vitamins and minerals is a guide by Dr Sarah Brewer who is the Medical Director at wellbeing brand Healthspan and Rob Hobson who is a Registered Nutritionist.

Vitamin D

What is it?

Vitamin D, or calciferol, is the collective term for five different, fat-soluble vitamins. The most important for human health are vitamin D2 (ergocalciferol) which is derived from plant foods and vitamin D3 (cholecalciferol) which is obtained from animal foods. These two forms differ in their side chain structure which makes vitamin D3 the better option for maintaining our vitamin D status.

Who’s deficient?

Those most at risk of vitamin D deficiency include:

  • Older adults – skin synthesis of vitamin D reduces with age so you produce at least 4 times less in your 60s compared to your 20s.
  • People who are frail and may have reduced appetite or poor diet.
  • People with limited sun exposure (housebound or those wearing long robes and head covers or using copious amounts of sunblock)
  • People with darker skin – the pigment, melanin, reduces the skin’s ability to synthesis vitamin D by neutralising some of the effects of UV light.
  • People with inflammatory bowel disease or other bowel conditions associated with malabsorption of fat (vitamin D is a fat-soluble vitamin).
  • Pregnant and breast-feeding women, breastfed infants (if their mothers have a low vitamin D status) and children under 5 years of age.
  • Obesity – as vitamin D is fat-soluble, a larger intake of vitamin D is needed to maintain adequate blood and tissue levels.

Lack of vitamin D is associated with significantly reduced bone mineralisation, which can lead to rickets in children and osteomalacia in adults. Bone thinning (osteoporosis) in menopausal women is also partly regulated by vitamin D status

 Signs of deficiency can include:

  • constipation
  • muscle weakness
  • irritability
  • depression
  • Increased susceptibility to infection.
  • poor growth
  • bone pain
  • bone deformities (in rickets)
  • deafness (in osteomalacia)
bone health - vitamin D
Vitamin D is important for maintaining healthy bones and joints.

Why we need it? 

The European Food Safety Authority has authorised health claims that vitamin D contributes to:

Normal absorption/utilisation of calcium and phosphorus

Normal blood calcium levels

The maintenance of normal bones

The maintenance of normal muscle function

The maintenance of normal teeth

The normal function of the immune system

The process of cell division

The normal growth and development of bone in children

A reduced risk of falling associated with postural instability and muscle weakness (a risk factor for bone fractures among men and women aged 60 and older)

And, together with calcium, helps to reduce the loss of bone mineral in post-menopausal women (a risk factor for osteoporotic bone fractures).

How does it work?

Vitamin D is a steroid hormone that interacts with receptors in the nucleus of certain cells to regulate the activity of certain genes. This regulates cell division and growth, as well as stimulating the production of proteins needed involved transporting calcium across the intestinal wall. In immune cells, vitamin D stimulates the production of antibiotic-like proteins and helps to regulate our defences against viruses and bacteria. 

Where do we can get it from?

You can make some vitamin D3 in your skin when exposed to sunlight. This is usually insufficient to meet your needs otherwise it wouldn’t be classed as a vitamin.

Vitamin D3 (cholecalciferol) is obtained from:

  • oily fish (sardine, herring, mackerel, salmon, tuna)
  • fish liver oils
  • liver
  • eggs
  • fortified milk
  • fortified margarine
  • butter
oily fish - vitamin D

How can I include it in my diet?

Rob Hobson Registered Nutritionist

It’s important to get vitamin D from your diet and, it can be found in useful amounts in oily fish, liver products, eggs, butter and fortified food. This can make it difficult for those following certain dietary regimes such as vegetarians and  vegans  who do not eat oily fish which is one of the best sources of vitamin D in the diet. 

Other sources are very limited, but you can get a little from fortified foods, eggs and mushrooms such as those harvested by the UK and Ireland mushrooms producers which have been grown under UV light.  Even though vegans do not eat oily fish this doesn’t necessarily make them more at risk of deficiency than omnivores as most of the population fails to eat oily fish on a regular basis anyway. 

You can also only get about 20% of your vitamin D intake from the diet and vegans can still glean some from fortified foods such as spreads and plant drinks. Everyone, regardless of dietary preference should invest in a vitamin D supplement during the winter months and this should be no less than 10mcg per day.  These supplements are also available in vegan friendly forms also.


The average Western diet supplies just 3mcg vitamin D per day and taking a supplement is widely recommended. The EU nutrient reference value for vitamin D is just 5mcg (200 IU) per day. Government guidelines recommend taking a supplement providing 10mcg (400 IU) per day during cold months of the year. 

These levels are based on the old understanding that vitamin D3 was just about calcium absorption to maintain healthy bones. Many experts now suggest that, in the absence of exposure to sunlight, an intake of 25mcg (1000 IU) to 50 mcg (2000 IU) is more appropriate for optimum immune health. EFSA says intakes of up 100mcg from all sources is upper tolerable level – consensus is that intakes of up to 75mcg per day long-term as supplements is okay. Do not exceed this dose except under medical advice.”

I recommend a supplement supplying 25mcg of Vitamin D for under 50s and 50mcg per day for those aged 50 and over. The upper safe level for long-term intake from both diet and supplements is suggested as 100 mcg (4000 IU) per day.  Vitamin D is sometimes expressed in International Units (IU) rather than micrograms. 1mcg vitamin D = 40 IU.

Vitamin D is included in multivitamin and mineral supplements usually in a relatively low dose of 5mcg to 10mcg per day.  Vitamin D is also available on its own in tablets, capsules, gummies and oral sprays.

What to avoid? 

Do not exceed manufacturer’s recommended dose except under medical supervision. Excess vitamin D can cause disturbances in calcium metabolism leading to headache, loss of appetite, nausea, vomiting, diarrhoea or constipation, palpitations and fatigue.

To find out further information about supplements or if you have any queries about taking supplements you can visit or speak to a qualified nutritionists.

For more instalments of the A-Z of vitamins and minerals see our nutrition channel.

Tags: Last modified: November 15, 2021

Written by 5:11 pm Nutrition