Health & Wellbeing

Vitamin D3 deficiency & vitamin D health benefits

Vitamin D3 deficiency & vitamin D health benefits

The second we start to notice the days are getting shorter, we begin hearing from every angle that we need vitamin D, and for good reason as a huge 50% of the global population are deficient. It's well known that as we see less of the sun, we need more vitamin D but is it clear why?

Vitamin D was discovered back in 1920 when it was unveiled as a possible cure for rickets, a painful childhood bone disease. We began fortifying foods with vitamin D, for example cow's milk and breakfast cereals, and rickets pretty much became a thing of the past. As a result of this, vitamin D is best known for its role in bone health by increasing intestinal absorption of calcium to 30-40%. Without vitamin D calcium absorption rates lie at around 10-15%. There are also many other areas of health which vitamin D can make a positive impact.

Vitamin D3 (also called Cholecalciferol) is one of five different forms of Vitamin D. Vitamin D3 and D2 are considered essential for human health. We need Vitamin D because it helps us to absorb calcium, magnesium, phosphate, iron and zinc from our foods. However, unlike other vitamins (which cannot be synthesised by the body and must therefore be ingested), Vitamin D can be synthesised by the body, when the skin is exposed to sunlight.

Sources of Vitamin D3

There are two ways of getting Vitamin D3 into the body - through exposure to sunlight or by ingestion.

Exposure to sunlight is our greatest source of Vitamin D3. The UVB radiation in sunlight enables a reaction in the epidermal layer of our skin to convert a compound, 7-Dehydrocholesterol, into Cholecalciferol (Vitamin D3).

Vitamin D3 can also be obtained through diet, but there are only a small number of foods that naturally contain it: alfalfa, lichen, fish liver oils, ‘fatty' fish species (salmon, mackerel, tuna, sardines), and eggs and beef and liver contain small amounts.

However, cholecalciferol is also produced industrially for use as a supplement and many ‘fortified' but processed foods, such as breakfast cereals, contain it.

How can we increase our Vitamin D intake?

Vitamin D exists in two forms, D2 which is naturally found in mushrooms and D3 the form most suitable for the human body. D3 is the form made in the skin when struck by UVB sunlight, it is also found in oily fish. Once we have formed the vitamin D or consumed it in the diet, it must first undergo hydroxylation in the liver, then again in the kidney to produce the biologically active form that stimulated increased absorption.

We're always told to supplement vitamin D in the winter as the days are shorter and we have less exposure to sunlight, however, realistically how often are you exposed to the sun from March to September? Before this year, most of us left the house on Monday-Friday to travel to work, likely spending most of that time in a vehicle or sitting in the office, spending an estimated 37 minutes outdoors.

As well exposure, there are a number of other factors that reduce formation of vitamin D:

  • Wearing sunscreen. Studies have shown that wearing factor 30 reduces vitamin D by 95%. This is by no means a recommendation to stop wearing sunscreen, as we are well aware of the benefits.
  • Skin tone. Individuals with darker skin tones have higher amounts of melanin which protects skin from the harmful effects of UV radiation and therefore reduces vitamin D production.
  • Age. Once in our system, vitamin D needs to be activated so our bodies can make use of it, this is done through the liver and kidneys. As we age, our kidney function naturally declines, therefore reducing the capacity to produce active vitamin D.
  • Breast fed infants. Vitamin D content in breast milk is dependent on the maternal status, therefore if a child is exclusively breast fed there is a risk of vitamin D deficiency.
  • Ability to absorb fat. Vitamin D is fat soluble and requires dietary fat to be absorbed in the gut, some individuals have a reduced ability to absorb fat which will have a direct effect on vitamin D status. Conditions which result in fat malabsorption include Crohn's disease, liver disease, cystic fibrosis, celiac disease and ulcerative colitis.
  • Gastric bypass surgery. This surgery bypasses part of the intestine where vitamin D is absorbed, significantly reducing vitamin D status.
  • Magnesium deficiency. Magnesium has a regulatory role of vitamin D and a deficiency can reduce vitamin D production.
  • Genetics. There may be variants in the gene involved in coding the vitamin D receptor, altering levels from person to person.
  • Obesity. Vitamin D is stored in fat in the body, however large amounts of fat can alter the release rate, resulting in an increased requirement for vitamin D.

Health Benefits of Vitamin D

We've covered bone health and its role in increasing calcium absorption, but there are a number of other benefits being researched. Aside from the obvious benefits of avoiding the health problems caused by Vitamin D deficiency there has, in recent years, been an increased interest in the other potential health benefits of Vitamin D3. There is evidence that Vitamin D could play a role in preventing/relieving a wide range of severe conditions:

Multiple Sclerosis

There some evidence that Vitamin D reduces your risk of developing Multiple Sclerosis (Munger et al., 2006 and Mokry et al., 2015 ), and may also help reduce relapse in those with the disease (Smolders et al., 2008). HeartDisease: studies have indicated that Vitamin D may help in decreasing your chance of developing heart disease (Wang, et al., 2008).

Colds and Flu

Some studies suggest Vitamin D3 can reduce the risks of people developing flu (Urashima et al., 2010). Parkinson's: A 2013 study found that supplementing with Vitamin D3 may reduce deterioration in people with Parkinsons (Suzuki et al., 2013)


A recent study suggests that there is a link between Vitamin D deficiency and cognitive decline (Miller et al., 2015)


Several studies indicate that lower levels of Vitamin D3 are associated with higher risks of various cancers, including colorectal cancer and breast cancer (Freedman et al., 2008; Garland et al., 2007; Giovannucci, 2007; Goreham et al 2007; Yin et al., 2009).

Cardiovascular disease

There is ongoing research into cardiovascular disease and there has been found to be an association between low levels of vitamin D and increased risk of heart disease and hypertension.

Immune system

Vitamin D is important in regulating antimicrobials in the body, these are substances that defend against disease-causing organisms, preventing them from living in the gut. The vitamin can also reduce inflammation caused by these nasty organisms, supporting the immune system. A deficiency in vitamin D can be linked to auto-immune and central nervous system (CNS) problems.


Seasonal affective disorder (SAD) is a type of severe mood disorder rearing its head in the winter, many of the symptoms are similar to depression including fatigue, difficulty concentrating, depressed mood and reduced libido. SAD occurs as a result of reduced sunlight, therefore a common treatment is light therapy and research studies have shown that symptoms may be managed through vitamin D supplementation.

As it is a relatively new area of research, there is still much to learn about any potential benefits of Vitamin D3, and many more studies are needed before the health benefits of supplementing with Vitamin D3 can be confirmed. However, the early indicators are very positive, and there is hope that, with further understanding of the effects of Vitamin D3 on the human body, we will potentially help to prevent deadly diseases and provide relief to millions of people suffering debilitating conditions such as Alzheimer's and Multiple Sclerosis .

Recommended Dosage

The daily recommended dose of vitamin D by the NHS for adults is 10 micrograms (ug), sometimes written as 400 international units (IU), this reduces to 8.5-10 ug for babies up to the age of 1. However, this is the minimum recommended intake assumed for a healthy individual, therefore requirements may vary significantly within a population and the optimal daily intake is considered to be around 25ug (1000 IU).

The upper tolerable limit for vitamin D, meaning the maximum daily intake considered to not cause any ill effects, is 100ug (4000 IU) for adults. Not all vitamins have an upper limit, however vitamin D is fat soluble meaning that excess will be stored in the fat and can build up to toxic levels causing unwanted side effects. Some possibilities with vitamin D toxicity are hypercalcaemia, where the body absorbs too much calcium, leading to nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, and kidney stones. In extreme cases of vitamin D toxicity there can be calcification of soft tissue e.g. coronary vessels, which are associated with cardiovascular complications.

How quickly do we produce Vitamin D?

As mentioned above, there are a number of factors that reduce vitamin D formation, but in a healthy individual the time required in lunchtime sun from March to September in the UK for an individual to stay above the deficiency level is 9-25 minutes depending on skin tone. This assumes that throughout June-August arms and lower legs are exposed, and throughout the other months hands and face are exposed to the sun. This time is just what is required to not be deficient and does not reflect the time required for optimal levels to be reached.

If you are concerned with your dosing or are at risk of deficiency, it is best to consult with your health care professional to check your blood levels.

Vitamin D3 Deficiency

A lack of Vitamin D results in impaired bone mineralization and bone damage which leads to bone-softening diseases such as Osteomalacia, also known as Rickets when it affects children. This condition can cause bending of the spine, bowing of the legs, muscle weakness, increased bone fragility and a higher risk of fractures. Pregnant and breast feeding women, children under the age of 5 years, older people over the age of 65 years, people who have low or no exposure to sunlight (for example, the house-bound) and people who have darker skin tones are more at risk of Vitamin D deficiency. In the UK, pregnant and breast feeding women are recommended to take Vitamin D supplements (0.01mg) daily.

Overdosing on Vitamin D3

It is impossible to overdose on Vitamin D by over-exposure to sunlight (which should always be avoided for other health reasons) as your body naturally stops producing and absorbing Vitamin D once it has reached equilibrium. However, though rare, people with existing medical conditions (such as hyperparathyroidism) can overdose on Vitamin D by ingesting large amounts of supplemental Vitamin D, causing a condition known as hypercalcaemia - where the body absorbs more calcium than can be excreted.

There is a delicate balance between too much and too little calcium in your blood, and therefore supplementation should remain conservative and within acceptable limits at present despite many doctors recommending a very high daily dosage.

Hypercalcemia may also be caused by:

  • Overactive parathyroid glands
  • Cancer.
  • Disease
  • Immobility.
  • Medications
  • Supplements (excessive).
  • Hereditary factors.
  • Dehydration (usually temporary)

Hypercalcemia can cause renal failure and irreversible kidney damage, as well as damaging bone tissue.

Before taking any additional supplements or making any changes to your diet it is always best to discuss it with your doctor first.

Share This