vitamin D & B12

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

However there are some deficiencies, especially in certain populations. In this post I'll cover two that can be of concern.



Vitamin D
One of the fat soluble vitamins, it is made in our skin when it is exposed to UV light and then transported in our blood to organs it effects. In foods it is present in cod liver oil, fatty fish (herring,sardine, 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 and that may be why those with metabolic syndrome have lower levels (1). Watch this space!

Who is at risk?
At least 50% of the worlds 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 risk, even with eating animal products, less than 5 micrograms (ug) of vitaminn D is available per day. 

Those with darker skin pigmentation require longer exposure to UV to have sufficient vitamin D levels, which can be difficult in places with less sun. 

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
First off there are different methods to increase your levels, with varying rates of success

Sun exposure
Is the quickest method of increasing your levels, in Australia this has to be done with caution. Some Doctors recommend getting exposure during times of the day with low 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 vtamin D toxicity (hypervitaminosis D) from the sun, you 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 adiposity. 
Oral supplementation is a slower method than UV exposure however may suit certain people better.

Food sources
Fatty fish

  • Egg yolks

  • Fortified margarines, milks etc



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

B12 supplies methyl (CH3) groups for DNA synthesis, as well as a providing essential cofactors which are required for the formation of myelin. Myelin is essential for your myelin sheath which protects peripheral, spinal and cranial nerves.

Your body has 2 enzymes that are dependent on there being available B12 to provide methyl groups for chemical reactions. One of these is involved in the formation of myelin
(methionine synthase) and the other is important in one of the bodies energy production cycles the the citric acid cycle (methyl malonyl mutase).

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 babies. 
People who have 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.

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

Poor dietary intake is typically from gut problems causing poor absorption. This form can lead to a form of anaemia called pernicious anaemia. Later stage deficiency causes neurological problems. 

Are you deficient?
As simple blood test will determine if your b12 stores have been depleted. B12 is a very small store in the body, however we use such minute amounts that it can take up to 2 years for the store to be depleted. 

Normal ranges are 200-900pg/mL.

Once it is depleted, it can cause serious health problems. 

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 byproduct

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



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. 

Stay tuned for more info on other vitamins and minerals and the risk of deficiency. Next vitamin E and C. 


  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.