Vitamin D

The Vitamin D Dilemma

Vitamin D – cholecalciferol (D3), ergocalciferol (D2)

Vitamin D is hormone like in its action, and is not considered to be a true vitamin. Despite it not being a true vitamin, it is still classed as a fat soluble vitamin – this means it is insoluble in digestive juices and requires bile for absorption, where it travels through the lymphatic system with chylomicrons (a lipoprotein/carrier protein) before entering the bloodstream. Vitamin D is stored in the liver and adipose tissue and is not readily excreted, increasing the risk of toxicity.  

Vitamin D and Bone Growth  

Vitamin D maintains blood concentration of calcium and phosphorus, the 2 minerals essential to bone mineralisation i.e these minerals help bone become stronger & denser. Vitamin D assists this in 3 ways:

1. 1. enhances absorption of calcium and phosphorus from the GIT
   2. enhances reabsorption of calcium and phosphorus by the kidneys
   3. mobilise of calcium and phosphorus from bones to blood through parathyroid directed regulation.  

Other functions of vitamin D 

Vitamin D is also involved found in tissues e.g immune cells, brain and nervous system cells, pancreas, skin, muscles, cartilage, reproductive organs.  

Vitamin D has numerous functions and may be valuable in treating disorders such as autoimmunity, anxiety and depression, tuberculosis, gum inflammation, multiple sclerosis and some cancers.

Vitamin D is gaining popularity in the treatment of a number of disease e.g diabetes, Paget’s disease, cardiovascular disease, osteoporosis and non-specific musculoskeletal pain.  

Making Vitamin D

Vitamin D is considered endogenous and sufficient exposure to sunlight allows the body to synthesise vitamin D from a precursor derived from cholesterol and sunlight. A cholesterol-based precursor produced in the sebaceous glands of the skin is converted to vitamin D with the assistance of UVB rays i.e sunlight. So you need sunlight to produce vitamin D. The same sunlight that is known to cause skin cancer.  Australia has some of the highest rates of skin cancer. This is where the dilemma is.

Australia is a sunburnt country. The Australian Cancer Council has been promoting the slip, slop, slap message, (slip on a shirt, slop on some sunscreen, and slap on a hat, for the uninitiated), for quite some years now. I don’t think anyone can argue that this is anything but wise advice.  

However, as even low SPF factor sunscreens can block UVB exposure, constantly using sunscreens increases the risk of vitamin D deficiency. Not only does sunscreen increase the risk of vitamin D deficiency, so does wearing thick clothing, e.g ‘veiled’ women, or spending most of your time indoors, e.g elderly people in hostels or nursing homes, or long stay hospital patients.

So how much sun is enough to increase vitamin D levels?

There is considerable controversy around this, but it has been suggested that exposing 10-15% of the body to the sun before 10am and after 3pm for 10 minutes between October and March (in Australia) is sufficient to supply adequate vitamin D. During other months up to 1 hour of exposure is needed. This short exposure can be achieved during brief outdoor tasks such as hanging out the washing, or walking to the mailbox, or sitting in the sun reading a book for 10 minutes. Do not make the mistake of ‘topping up’ your exposure on any one day, as this will increase the risk of sunburn and skin cancer. Stick to the 10-15 minute rule, even the Australian National Health and Medical Research Council (NMHRC) agree that this is adequate sun to keep vitamin D levels up in most healthy people.

Vitamin D is also found in cold water fish oils such as halibut, herring and tuna, egg yolk, sprouted seeds, and foods that have been fortified with vitamin D e.g milk, milk products, some cereals and breads.  

Recommended Daily Allowance (RDA)

The RDA for vitamin D is 200-400iu or 5-10µmg per day. Therapeutic dose starts at 1000iu or 25µmg per day and can be as high as 10,000iu or 250µmg per day.

Allowances for vitamin D can be averaged out over time and don’t have to be consumed regularly like water soluble vitamins.

Those people who have reduced exposure to the sun, can supplement their diet with vitamin D. However, be aware that ingested vitamin D is only 50-80% bioavailable i.e you will only absorb 50-80% of what you ingest.

Vitamin D Deficiency

Deficiency of Vitamin D most commonly shows as Rickets and/or osteomalacia.

It’s worth noting that studies have indicated that between 75-90% of Australian adults are deficient in Vitamin D, although Rickets is rare.  

Deficiency should be considered in patients with poor fat metabolism – this is because vitamin D is a fat soluble vitamin. People with low exposure to sunlight may also be vitamin D deficient e.g people whose clothing limits exposure, people in cold climates. Because of its links to the parathyroid, vitamin D levels should be assessed if there is parathyroid dysfunction. Those most at risk of vitamin D deficiency, i.e people over 50 years of age, people with malabsorption problems such as those seen in coeliac disease.

Vitamin D and Genes

There are a number of genes which influence the production, transportation and utilisation of Vitamin D. Knowing an understanding a patient’s genetic profile is a core component to treating the underlying cause of Vitamin D deficiency. For example, if a patient has genes which code for poor uptake of Vitamin D, then it is necessary to supplement with high doses of Vitamin D to correct deficiency.

Excess vitamin D

Too much Vitamin D can lead to calcium imbalance e.g calcification of soft tissue and formation of stones, seizures, disorientation, joint pain. Supplements may cause toxicity – for this reason you should consult a healthcare professional trained in human nutrition before taking a Vitamin D supplement.

If you feel that you may be at risk of vitamin D deficiency, consult a healthcare professional trained in human nutrition.The Naturopaths and Herbalists Association of Australia (NHAA) and the Australian Traditional Medicine Society (ATMS) list accredited practitioners (naturopath, herbalist or nutritionist) who can correctly prescribe vitamin supplements.  

Reference: 

Herbs & Natural Supplements: An evidence based guide (3rd Edition), by Lesley Braun and Marc Cohen.  The Nutrient Bible (6th Edition), by Henry Osiecki.