A hot topic right now is Vitamin D and how much sun exposure we require for Vitamin D synthesis to take place.  The jury is out on this subject, with many conflicting points of view causing much confusion:  people are being told they need more sun exposure to increase their Vitamin D levels, or put themselves at risk to certain cancers. As much as we love our photograph this month, courtesy of a Johannesburg-based professional photographer, of blue skies blending into a never-ending blue horizon, we cannot afford to spend too much time in the sun with the excuse that we all need to top up our Vitamin D levels.  Too much sun exposure causes skin cancer, of that there is no doubt and we are worried that some people are being told to increase their sun exposure in order to top up their Vitamin D levels.   As promised previously, Dr Webster will give you his thoughts on this matter:

Vitamin D is inexorably linked to human evolution.  The most favoured, current theory about human evolution is that all modern man i.e. Homo sapiens, originated from Africa and moved out of Africa to the rest of the world.  Approximately 70 000 years ago, there was the Toba super volcanic eruption on the island of Sumatra.  This produced a huge ash cloud over the whole world and produced an approximate decade long volcanic winter.  This resulted in a massive dying out of the modern human population, leaving a small remaining population of a possible 10 000 individuals.  It is thought that most of these individuals were in Africa.  This is called the ‘bottle-neck’ in human evolution.  It is interesting that the San people of South Africa have the greatest genetic diversity and they are rightly called the ‘first people’ – it is thought that the geographical origin of all modern humans is south-west Africa, on the coastal border between Namibia and Angola.

Man who moved out of Africa would have had a darker skin and as he moved further north, by natural selection, his skin would have become lighter.  Vitamin D is required for the normal functioning of the body and a Vitamin D deficiency in children causes rickets and in adults it causes osteomalacia, a bone disorder.  Humans with a lighter skin are able to produce Vitamin D in the skin with lower levels of UVB.  In other words, in the absence of high diet of Vitamin D, man with a darker skin would have been more likely to develop rickets or osteomalacia the further north he went.  Rickets, in women, would have produced an abnormally shaped pelvis and these women in all likelihood would have died in childbirth.

Therefore by natural selection, humans with a paler skin would have survived better in the more northern hemispheres. It is interesting that the Neanderthals who inhabited the northern hemisphere but who eventually died out, did in fact have a paler skin with reddish/blonde hair. The one exception to this are the Inuit, who have a darker complexion and are able to survive in the far northern hemisphere;  the difference here is that the Inuit have a very high dietary intake of Vitamin D, due to the fish that they catch and this has ensured their survival.

The two sources of Vitamin D are dietary intake and the production of Vitamin D in the skin from UVB radiation.  Unfortunately very few foods in nature contain Vitamin D.  The best source of Vitamin D in food is to be found in oily fish such as salmon, tuna, sardines, mackerel, flaxseed and egg yolks.  In addition, some dairy products and cereals may be fortified with Vitamin D.

The bottom line is all about achieving the balance for the individual: between exposing oneself to enough sunlight to maintain adequate Vitamin D levels and avoiding an increase in the risk of skin cancer.  During the summer months, most people should be able to achieve adequate Vitamin D levels through incidental  outdoor exposure outside peak times. For example, for someone who burns easily in the sun, they may only need 5 minutes of sun exposure each day before 11.00am and after 4.00pm (to the face, arms and forearms) to achieve adequate Vitamin D levels.  Conversely, someone who tans easily or has a darker skin type, will need more time, for example, up to 20 minutes.  The liver stores Vitamin D and these stores can be used by the body during the winter months.

Deliberate exposure to sun at peak UV times is not recommended as this increases the risk of skin cancer, eye damage and photo-ageing.  It is thought that Vitamin D production is more effective while doing exercise.  It is good to be aware that UVB is absorbed by glass i.e. your skin will not produce Vitamin D while you are driving your car with your windows closed.

It is impossible to give universal guidelines but if in doubt, one can have a blood test to check your Vitamin D levels.  My recommendation would be a healthy, balanced diet that would include some oily fish, to take one good multivitamin each day and contained in these multivitamins would be Vitamin D of a dosage of between 400 and 600 IU daily.  If your Vitamin D levels are found to be low, I would recommend that you consult a dietician to advise you on  achieving normal Vitamin D levels and then maintaining them.

I run in the mountains near my home early in the morning twice a week for approximately one hour. I do not use a sunscreen at that time and I take one good multivitamin daily as well as Environ Omega 3 and I also have a well-balanced diet.  I recently had my blood tested and my Vitamin D levels are perfectly normal.

Dr Ian Webster

June 2012




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