I've been following this for a while ever since I read that the Crohn's disease I suffered from in the 70s (long since cured I hasten to add) might be caused by a predisposition to the ill effects of vitamin deficiency. My recent reading around the subject has unearthed some very interesting findings that are about to burst onto an unsuspecting public. It turns out that a long-term epidemiological study (led by the Department of Nutritional Sciences, and Department of Laboratory Medicine, University of Toronto) reveals that Vitamin D deficiency is likely to be as chronic a deficiency in "First World" societies today as Vitamin C deficiency was to scurvy-prone sailors of old.
It appears that in first world countries (especially those in the mid to northern latitudes in the northern hemisphere and mid to southern latitudes in the southern hemisphere) we humans, despite our primary adaptation to fairer skin following our exodus from our equatorial sun-drenched African "nursery", have not yet fully adapted/evolved to the lower levels of sunlight (more specifically the UV-B component) of temperate latitudes. Evolution, for good or bad, has dictated that daily exposure of the skin to UV-B radiation is necessary to maintain a healthy level of Vitamin D in our bodies. This vitamin is naturally available in natural fish oils but to consume sufficient to overcome the effect of UV-B deficiency risks poisoning by it's fish oil accompaniment, Vitamin A. [This does beg the question however - How do Inuits cope?] When, during pre-civilised society, our normal lifespans were relatively short, the fair skin adaptation was all that was needed to enable sufficient Vitamin D build up to attain sexual maturity and thus to procreate. However, as modern civilised society allows us to live considerably longer lives, the hidden vagaries of chronic Vitamin D deficiency appear to be coming more to the fore as indeed the epidemiological studies of the University of Toronto et al are now revealing - evidence that the slow mysterious upsurge of numerous so-called first world diseases is likely to be a manifestation of this deficiency.
A very large proportion of the human race is considered to be officially deficient in Vitamin D. Indeed it appears that mid to northern/southern latitude populations are running on empty during the winter months. This is because, despite even taking care to maximise outdoor exposure, the low maximum sun elevation, the short daylight hours and propensity to longer periods of cloud cover, combined with the near full skin cover of winter clothing means that UV-B skin absorption is minimal.
Epidemiology shows that especially bad deficiencies occur in black races who in evolutionary terms have moved to less sunny climes overnight and whose higher skin pigmentation means that they are prone to even greater degrees of UV-B / Vitamin D deficiency.
Epidemiological evidence also shows that head-to-toe cover of Muslim women in the Middle East where sunshine is more prevalent (and so Vitamin D deficiency should be less chronic) is associated as one might expect with the extreme Vitamin D deficiency disorder - rickets, but also, the first world ailments are taking hold there too.
In sun-drenched Australia where the universal use of sunblock has been so successful in reducing incidence of skin cancer, it now appears that this same sunblock is playing a negative health role contributing to a recent burgeoning of typical Vitamin D deficiency disorders.
So what are these disorders? The epidemiological study has revealed clear wide-ranging correlations, in the same way (though in a broader sense) that smoking-related cancer statistics did a generation ago. These principal burgeoning afflictions (but not exhaustive) are: diabetes, forms of cancer especially colon cancer, eczema, asthma, muscular sclerosis, types of renal failure. And the statistics cry out that these disorders are especially prevalent in darker skinned races. The body of evidence also shows that the old belief that it is easy to overdose on Vitamin D is not born out by any recent scientific studies, especially when the oral Vitamin D is not accompanied by Vitamin A as it used to be (upon which it is very easy to overdose) and rather, is administered in the synthetic form of Vitamin D3 (cholecalciferol). [The older D2 (ergocalciferol) synthetic form has lower bioactivity, poorer stability and shorter duration of action, and so is no longer recommended.] The evidence also shows that premature deaths in old age simply as a result of the secondary complication of broken thigh bones/hips is far rarer in individuals less deficient in Vitamin D, as the vitamin promotes more efficient calcium uptake so warding off osteoporosis. The vitamin's deficiency also appears to be implicated in neuro-muscular degeneration of old age.
Apparently, a majority of us would largely lead just as healthy lives without the unnecessary daily vitamin and mineral tablets we are prone to taking - however, the epidemiological evidence does now point to Vitamin D3 as being the one vitamin above all others that we should all self-administer from childhood onwards, because practically there is no other way of absorbing it.
Vitamin D3 can often be found available as single 25 micrograms tablets. The Toronto University study shows that one or preferably two of these should be taken daily throughout the year - however, if taken only during the winter months would still largely overcome the deficiency and its symptoms.
So........I'm sold on all this that's for sure. Suggest you read around the subject yourself. Probably too late for me in many respects, but will continue to take 50 micrograms per day if only to maintain bone density!
http://wildhorse.insinc.com/directms13oct2005/
This is a very informative lecture. Bear with the annoying flashing up of blank pages as the slides change - just click off each time to continue viewing.