vitamin D & B12

The supplement industry is a multi-million dollar business, however many of the supplements are unnecessary when people eat a diet high in vegetables, fruit, whole grains and lean meats. 

If you live in a country that has a functioning food system and can afford to eat, you are unlikely to be deficient. There are still some deficiencies people can suffer from, especially in specific populations. In this post we'll cover two that could be of concern.

Vitamin D
One of the fat-soluble vitamins, vitamin D is made in our skin when exposed to UV light waves. The vitamin D is then transported to the parathyroid where it is activated, and transported to the tissues/structures it has an effect on (bones, kidneys and small intestine).

In foods vitamin D is present in cod liver oil, fatty fish (herring, sardines, salmon), eggs, red meat, liver and fortified foods such as margarine and milk. 

It has roles in maintaining extracellular (outside of cells) calcium concentration, along with parathyroid hormone and calcitonin. Which means it has an important role in osteoporosis prevention. People who are obese have been found to have low vitamin D levels, there is on-going research into the link between vitamin D, calcium, the thyroid and the obesity epidemic. Some suggestions are that those with higher body mass require higher levels of vitamin D as it is stored in fat tissue at a higher rate. This may be why people who are obese or overweight have lower levels (1). Research in this area is very much watch this space.

Who is at risk?
At least 50% of the world’s population could be deficient. Studies in the US and UK have shown at least 19-16% of adults are deficient.
Unsurprisingly, people who live in tropical and sub-tropical regions generally make enough vitamin D, unless they cannot leave their home (the elderly) or traditionally completely cover their skin. 

Those who live in the more northern and southern latitudes with limited sun exposure can be deficient in vitamin D. Those who live in these regions and traditionally cover their skin are at even higher risk of deficiency. 

At some latitudes not enough sunlight during winter months means supplementation is necessary. Vegans are also at higher risk, as the foods naturally high in vitamin D are animal products. Even when eating animal products, less than 5 micrograms (ug) of vitamin D is available per day. 

People with darker skin require longer exposure to UV to have sufficient vitamin D levels, which can be difficult in places with less sun, or with traditional clothing in some cultures.

Are you deficient?
First off establish if you are deficient, a blood test at your local GP will let you know if you are low. 
50 nmol/L and higher is normal. (2)

Safely increasing levels
If you find you are low in vitamin D, there are a couple methods to increase your levels, with varying rates of success

Sun exposure
Is the quickest method of increasing your levels, in Australia and New Zealand this has to be done with caution. Some Doctors recommend getting exposure during the times of the day with the lowest UV without sunscreen on. Sunscreen can prevent your skin absorbing the correct UV. 

Oral supplementation
D3 is the chemical form typically used in oral supplementation. It is important to note that although you cannot get vitamin D toxicity (hypervitaminosis D) from the sun, some people can get it from supplements. Infants are at particular risk, even at 50 micrograms/day (50ug/day). 

Research is suggesting there is a link between body weight and dose, therefore the upper level of 50 ug/day may be overly cautious for those with higher fat levels. 
Oral supplementation is a slower method than UV exposure however may suit certain people better.

Food sources

Fatty fish
Egg yolks
Fortified foods such as margarines, milks etc

One of the water-soluble vitamins, B12 is only found in animal products. B12 is only in animal products as it always has to be bound to protein. Some algae and bacteria can also make B12. (3)

B12 supplies methyl groups (CH3) for DNA synthesis, as well as a providing cofactors (essential parts of chemical equations) that are required for the formation of myelin. Myelin is essential for the myelin sheath, which protects the nerves in the spine and head.

The 2 enzymes that are dependent on B12 supplying enough methyl groups are methionine synthase (myelin formation) and the other is methyl malonyl mutase, (important in energy production).

Who is at risk?
Individuals who struggle to consume animal products or don't consume animal products at all are at risk, these include the elderly, vegans and infants. 
People with atropic gastritis, pernicious anaemia or an autoimmune condition are also likely to be deficient.

Vegans are especially prone to deficiency as B12 is stored in tiny amounts, it takes roughly two years for the pool to be depleted but once it is, people can expect to feel lethargic and tired.

Infants breastfed by strict vegan mothers are also at risk of deficiency which can harm neurological growth.

Poor dietary intake can typically be from gut problems causing poor absorption. This form of deficiency can lead to a form of anaemia called pernicious anaemia. Later stage deficiency causes neurological problems. This may include nerve damage, symptoms will include loss of balance, weakness, dizziness and vision problems

Are you deficient?
As simple blood test will determine if your b12 stores have been depleted. B12 only has a very small store in the body, with eating enough this does not present an issue as we use tiny amounts. As we use such small amounts, it can take up to 2 years for the store to be depleted. 

Normal ranges are 200-900pg/mL.

Safely increasing levels
Oral supplementation
Supplementation is a safe route to increasing b12 stores. Some foods are also fortified with b12. For breastfed vegan infants, supplementation is essential. Large amounts are safe.

Food sources

  • All animal products

  • Some algae and bacteria produce b12 as a by product

  • Be careful of some vegan supplements, spirulina has high quantities of an inactive form of b12 and may not be effective.

Take Away
It is always best to determine deficiency when possible from a blood test before buying and taking supplements. 

Modern lifestyles and diet choices can have an impact on vitamin stores. Getting outdoors, exercising and eating a complete diet helps prevent deficiencies. 


  1. Ekwaru JP, Zwicker JD, Holick MF, Giovannucci E, Veuglelers PJ. The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers. PLOS ONE. 2014 Nov 5; 9(11): e111265

  2. Truswell S. Vitamins D and K. In. Mann J, Truswell S, editors. Essentials of Human Nutrition [Print]. Oxford: Oxford University Press; 2017.

  3. Truswell S. The B Vitamins. In. Mann J, Truswell S, editors. Essentials of Human Nutrition [Print]. Oxford: Oxford University Press; 2017.