Vitamin D Deficiency Behind Many Western Cancers?

twilight30 wrote us with a link to an article in the Globe and Mail. If further study bears out the findings, new research into the causative agents behind disease and cancer may have a drastic impact on the health of citizens in Canada and the US. According to a four-year clinical trial, there's a direct link between cancer and Vitamin D deficiency. "[The] trial involving 1,200 women, and found those taking the vitamin had about a 60-per-cent reduction in cancer incidence, compared with those who didn't take it, a drop so large — twice the impact on cancer attributed to smoking — it almost looks like a typographical error. And in an era of pricey medical advances, the reduction seems even more remarkable because it was achieved with an over-the-counter supplement costing pennies a day. One of the researchers who made the discovery, professor of medicine Robert Heaney of Creighton University in Nebraska, says vitamin D deficiency is showing up in so many illnesses besides cancer that nearly all disease figures in Canada and the U.S. will need to be re-evaluated. 'We don't really know what the status of chronic disease is in the North American population,' he said, 'until we normalize vitamin D status.'"

Re:Confusing

[aussie_a]

Yes. You see sunlight, like many things, [wikipedia.org] too much of something can be lethal.

Re:Confusing

[mavi_yelken]

According to the article, Vitamin D deficiency causes whole other nasty types of cancers of body like colon, breast etc. Skin cancer has a much better prognosis then the cancer of the inner body.
Also, we evolved in Africa. Surely evolution found a balance between cancer of skin and Vitamin D synthesis? Also, color of skin is basically the answer of natural selection to the latitude your ancestors migrated to.

Come get some

[Anonymous Coward]

What are the sources of vitamin D?

Fortified foods are the major dietary sources of vitamin D.4 Prior to the fortification of milk products in the 1930s, rickets (a bone disease seen in children) was a major public health problem in the United States. Milk in the United States is fortified with 10 micrograms (400 IU) of vitamin D per quart , and rickets is now uncommon in the US.7

One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin for adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and ice cream are generally not fortified with vitamin D. Only a few foods naturally contain significant amounts of vitamin D, including fatty fish and fish oils 4. The table of selected food sources of vitamin D suggests dietary sources of vitamin D.
Exposure to sunlight

Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin.7,8 Season, latitude, time of day, cloud cover, smog, and suncreens affect UV ray exposure.8 For example, in Boston the average amount of sunlight is insufficient to produce significant vitamin D synthesis in the skin from November through February. Sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen whenever sun exposure is longer than 10 to 15 minutes. It is especially important for individuals with limited sun exposure to include good sources of vitamin D in their diet.

Re:Confusing

[**loki969**]

It seems that one needs to have a minimal amount of direct and "strong enough" sunlight on naked skin each week to have a sufficiant vitamin D3 supply. According to Wikipedia [wikipedia.org] the minimal amount of sunlight is ten to fifteen minutes twice a week at sea level when the sun is more than 45 above the horizon. So skin cancer shouldn't be much of a problem.

I have to admit that after reading the headline, I was sceptical too. But after doing some reading, it seems to me that this story does make sense.

Re:Yeah...

[Anonymous Coward]

Hmm, this is an interesting thought. If this Vitamin D theory is correct then those who are the least able to produce Vitamin D from sunlight should have the highest incidences of cancer--meaning those in the northern climates and those who have darker skin colors.

60% reduction in risk?

[aschoff_nodule]

I believe that Vitamin D might protect against some cancers.

However, I do not agree that Vitamin D deficiency can be responsible for about 60% cancers.

Here are my reasons why:

1) The process of carcinogenesis (initiation of the first DNA mutation/ adduct required to form cancer to the stage of clinically overt disease) in most cases takes more than 4 years. This clinical trial is only 4 years and too premature to reach to conclusions.

2) I have yet to read the paper, but it is necessary to know whether this trial was truly randomized meaning that the those who got the Vitamin D pill and those who got the placebo were similar to each other in all other ways. It is possible that if it is not randomized, a healthier cohort of people chose to take Vitamin D for a long time.

3) It is also important to know how they treated those people who dropped out of taking the Vitamin D pills. It is possible that unhealthier people dropped out and then we were comparing all subjects in the placebo group to the "healthier" people in the Vitamin D group.

4) A risk reduction of 60% (= relative risk of 0.4) is epidemiologically very strong and if that was the case, we would have already found such a role of Vitamin D much earlier (like 30 years before or so). There is something called Bradford Hill's criteria for causation in epidemiology which has strength of association as one of the criteria. The rationale for that is if we had a confounder which is actually responsible for the effect, we would have known it before because it is more likely to have a stronger effect. The same principle goes here. We do not know anything that could prevents so many types of cancer with such great attributable fraction. The magnitude of effects of like 2.5 or reduction of risk to 0.4 were the strengths we used to see in the papers of 1970s. Hence I think there could be some issues with the study design and data analysis of this study if they found such a great magnitude of effect.

Having said that I think that Vitamin D might prevent many cancers, but I expect a lower magnitude of the effect.

   

Quick Physiology Lesson

[mrbluze]

I think I'll head off to the pharmacy.

Not so fast ;)

Vitamin D is a fat soluble vitamin and is present in meat products. Deficiency in Vitamin D causes rickets [wikipedia.org]. Vitamin D is so-called, and many would think it was not available without a dietary source, but it is produced in the skin under the influence of UV light. It then gets processed by the liver, then 'activated' in the kidneys and off it goes and does good things.

Because it is fat soluble, it is unlike Vitamin C in that stores are steady and no Vitamin D production only starts to cause problems after several months.

Whilst Vitamin D requirements increase with age, sun exposure commonly decreases with age, especially in the elderly. Much of this is simply a lifestyle issue.

Importantly, Vitamin D is already known to have immunomodulatory activities (a well functioning immune system is critical in preventing cancer over time). It is also known to induce some cancers to self-destruct.

Go outdoors for a few minutes

[giafly]

Only brief full-body exposures to bright summer sunshine -- of 10 or 15 minutes a day -- are needed to make high amounts of the vitamin. But most authorities, including Health Canada, have urged a total avoidance of strong sunlight or, alternatively, heavy use of sunscreen. Both recommendations will block almost all vitamin D synthesis.

Those studying the vitamin say the hide-from-sunlight advice has amounted to the health equivalent of a foolish poker trade. Anyone practising sun avoidance has traded the benefit of a reduced risk of skin cancer -- which is easy to detect and treat and seldom fatal -- for an increased risk of the scary, high-body-count cancers, such as breast, prostate and colon, that appear linked to vitamin D shortages [my highlights].

The sun advice has been misguided information "of just breathtaking proportions," said John Cannell, head of the Vitamin D Council, a non-profit, California-based organization.

Our modern diet is very different from what we evolved to eat. Better in some ways - few Westerners starve - but probably lower in many micronutrients [wikipedia.org] than the ideal. So this type of report is not a surprise. Expect more.

Re:now the counter argument... ?

[Anonymous Coward]

There's strong evidence, in fact, that the reason people that moved away from the equator developed paler skin was to maintain high production rates of vitamin D. So, quite frankly, even if the intake of vitamin D killed us, we'd have to have it as if we don't take it we die anyway, therefore the entire point is moot.

The 'skin colour' and latitude argument has been dismissed already by evolutionary biologists, not least because humans haven't actually been in Northern Europe for long enough for evolution to have played a role in developing the pale skin colour found there. In fact, American Indians have lived on the Equator in America for longer, yet they are lighter coloured than say, Africans.
As Jared Diamond puts in his book The Third Chimpanzee [wikipedia.org] The variations we see in humans are more likely caused by the genetic variation of a few early settlers.
So please be careful when quoting 'strong evidence' when this is clearly not the case. Even Darwin was dismissive about this relationship.

There's some truth to this...

[Eggplant62]

The doctor that I work for has asked me to research this very line of thinking for her, pulling every article out I could find on multiple sclerosis (MS) and Vitamin D, and I even ended up using some of that research in a paper I wrote for an English class.

There's a very significant link between Vitamin D deficiency and MS. Most MS cases occur in the far north and far south climes. Think of southern Australia and Tasmania and northern Europe and United States, areas where sunshine is at low levels for as much as nine to ten months out of the year. We are able to make Vitamin D via sun exposure on the skin, which for humans, is a primary source of Vitamin D. Some of these studies find that people who had high levels of sun exposure as children greatly reduces their risk of contracting MS.

Don't believe me? Read these studies. There are tons more just like them, confirming the suspicion.

Re:Just from personal experience ...

[Anonymous Coward]

The number of cases each year in the USA of breast and lung cancer are about equal, but the death rates are in the ratio of approximately 1:4. In other words you are much more likely to survive breast cancer. So this suggests that the effort should be on preventing lung cancer cases if the goal is to save the maximum number of lives. The implication is relatively simple: encourage people not to smoke. In any given year lung cancer currently kills twice as many women as breast cancer.

Re:now the counter argument... ?

[Detritus]

The Food and Nutrition Board of the Institute of Medicine has set the tolerable upper intake level for adults at 2000 IU. Going higher than that may cause problems.

http://ods.od.nih.gov/factsheets/vitamind.asp [nih.gov]

Re:There's some truth to this...

[solanum]

Think of southern Australia and Tasmania... ...where sunshine is at low levels for as much as nine to ten months out of the year.

You are joking, southern Australia gets huge amounts of sunlight thus it has the one of the worlds highest rates of skin cancer. Don't forget that the latitude of the south coast of Australia is only about 36 degrees and that the southern hemisphere receives more sunlight than the northern hemisphere due to the eccentricity in the earth's orbit (and angle of axis). Most people in southern Australia have difficulty getting enough sunscreen on year round rather than getting enough sun exposure.

We are Caucasians.

[Futurepower(R)]

Our white skin color comes from the Caucasus mountains, north of Iran. That's why white people are called Caucasians. I had a woman friend whose ancestry was from northern Iran, and it was amazing to see how white she was, in a way I thought was beautiful. Comparing her skin and mine, it was easy to see that I am a mixture of Caucasian and something else.

Probably the reason northern people are white is that black people inter-marrying with a high concentration of white people tends to produce lighter-skinned new generations.

All humans apparently spread from an original migration from Africa, but the people who initially migrated tended to continue to migrate, and migrated much more than those who initially stayed in Africa.

Re:I am suspicious. - I am not, no money in it

[harvey the nerd]

Vitamin D3 (the good version) costs about 2c - 5c per 1000 IU tablet (2.5x RDA) at places like Costco, Swansons, Puritans Pride, Sams Club, Walmart etc depending on size bottle and frequent specials. Huge obscence profits, conspiracy to take over the world (sarcasm). However in northern latitudes like Canada, Alaska, Scandinavia, northern Russia, these are very basic health issues worked in a number of mainstream North Am medical schools despite rampant anti-vitamin politics. Score one for the med school researchers over the drug addled (and coddled) managements. I take mine with vitamin K and mixed tocopherols, the natural isomeric mixtures of vitamin E, all cheap online as well as separately with a *good* multivitamin without iron (like many men, I already had excess).

Re:Yeah...

[Knutsi]

So you would expect the rate of skin cancer among Ghaneans in Trondheim (for example) to be soaring. Then again, Norway has one of the best medical systems in the world, but you'd at least expect to see a correlation.

According to this article [newhope.com], there is. The article is well written, and quotes the reference on this particular point to be:

Angwafo FF. Migration and prostate cancer: an international perspective. [nih.gov] J Natl Med Assoc 1998 Nov; 90 (11 suppl):S720-3.

Re:now the counter argument... ?

[noemore]

http://en.wikipedia.org/wiki/Gloger's_rule [wikipedia.org] that's my counter arguement.

Re:now the counter argument... ?

[arivanov]

Disagree.

In the UK, in same nursery as my kid when he was 3 there was at least one case of Rickets worse than anything I have seen in the 3rd world. Locally born, locally grown.

The really disgusting point here is that the nursery in question was running the daycare for a UK health trust so the child was a child of UK healthcare professional.

All symptoms - skull deformity, chest deformity and O-legs so pronounced that a small dog could jump through between the knees when the child was standing straight with heels together.

And that is not the only one I have seen in the UK (though clearly the worst one).

I agree with you regarding the presense of D in the diet, but there is an important point here - when taken in its normal form it requires activation by UV in the skin. Only formula milk contains preactivated D (aka D3). Even most vitamin supplements contain the non-active form. In order for it to be activated one should get at least 35 mins unhindered (no cream) summer sun per day in UK lattitudes (on average for a caucasian white, adjust up for a darker skin). Currently, the schools and nurseries splat kids with factor 32+ and do not allow them out without it (and/or mandate long trousers and long sleeve in the summer months). As a result, how much vitamin D you have taken in food is irrelevant, it is not getting activated.

Actually I can a dark colored race in the north

[SerpentMage]

Inuit... Inuit have relatively dark colored skins...

http://www.smh.com.au/news/world/climate-forces-in uit-onto-thin-ice/2006/05/26/1148524886121.html [smh.com.au]

And Inuit have been living in the North for many thousands upon thousands of years (50,000 I think). Actually I am always amazed at how dark their skin is comparing to where they live. It's not like you are going to see a bunch of Inuit suntanning on the tundra...

A skin near the equator that is light colored? Hmm... How about Amazon natives? http://bbs.keyhole.com/ubb/z0302a1700/amazon.jpg [keyhole.com]

The Amazon is about as close to the equator that you can get and their skin is relatively light colored when compared to say the skin color of an individual from Africa. And last I heard Amazon natives have been there for many many many thousands of years.

So the nutshell is equator = darkness of your skin color is HOGWASH! Want me to prove it even further? How about the aboriginals of Australia when compared to an individual from Malaysia? Aboriginals are much much darker and further away from the equator than individuals from Malaysia....

Huh? Do You Know How Inuit Live?

[SerpentMage]

The Inuit skin is darker because they have historically lived in the snow reflecting light... Huh? Sorry dude, but do you know where the Inuit actually live? They live above the arctic circle meaning that when there is snow for the most part (6 months) it is dark, and thus their Vitamin D reserves would have been used before the sun could replenish it. Then when there is sun the snow melts and there is very little reflection giving them a "sun tan."

Re:Actually I can a dark colored race in the north

[shawb]

My guess for the Amazon natives having lighter skin would be that they live in the jungle? Not out in the plains, and so they would still be receiving less sunlight than people living in the Savannah. Just a guess, but it fits with the theory.

Bingo. Dense rainforest canopies block a very significant amount of light. IIRC about 5% makes it through to the lower levels where people would reside. Jungles are quite dark, something that doesn't come through in pictures and movies due to compensating with exposure time and aperture size.

Re:60% reduction in risk?

[Anonymous Coward]

Ironically, if you'd RTFA, you'd know that you can't RTF Study yet--it's due to be published in June.

Re:now the counter argument... ?

[happyemoticon]

That's funny, cause I taped some lectures at a major research institution back in '04 where an evolutionary biologist cited the link between skin color and latitude. So apparently not all evolutionary biologists subscribe to this belief.

Too little sun exposure causes a Vitamin D deficiency. When women have Vitamin D deficiencies, they become less fertile. And interestingly, if I recall correctly, too much sun exposure interferes with women's antral follicle development - the ones in the ovaries, not on the skin. Therefore, there is the potential for selective pressure to be both not too dark and not too light.

Is natural selection - note that I said Natural Selection, not evolution - fast enough to cause the suppression of darker-skinned people at the poles and lighter-skinned people at the equator? Well, if I started off with a population where everyone's blood type was either AB, A, or B, and I sterilized all of the people with B alleles, the population would soon be all type A. No other factor has as direct an impact on a population's genes than fertility, by definition. Forget skin cancer. Skin cancer won't prevent most people from having children. Having no viable eggs will.

So nobody's saying those strange cosmic rays created the variation we see in people's skin tones. But it's daft to push aside the direct impact that skin color and latitude have on fertility, and the large body of circumstantial evidence we have in the form of human geography.

Re:now the counter argument... ?

[buswolley]

I perused the PubMed research database and came back with a number of research studies providing a substantial amount of converging evidence that Vitamin D reduces the incidence of many types of cancer:

Here are a few of them:

Humble, M. (2007). [Vitamin D deficiency probably more common than earlier apprehended. Prevention and treatment could result in unexpected public health effects]. Läkartidningen, 104(11), 853-7.

Nielsen, LR, & Mosekilde, L. (2007). [Vitamin D and breast cancer]. Ugeskrift for læger, 169(14), 1299-302.

Ondková, S, Macejová, D, & Brtko, J. (2006). Role of dihydroxyvitamin D(3) and its nuclear receptor in novel directed therapies for cancer. General physiology and biophysics, 25(4), 339-53.

Garland, CF, Gorham, ED, Mohr, SB, et al. (2007). Vitamin D and prevention of breast cancer: pooled analysis. The Journal of steroid biochemistry and molecular biology, 103(3-5), 708-11.

The results also makes sense in evolutionary terms.

Tanning Industry Hoax!

[reversible physicist]

The "controversy" about the health benefits of sun exposure is fueled mainly by the tanning industry. All of the large studies on which the health benefit claims are based (including the one cited here) used oral vitamin D, not sun exposure. To quote from the abstract of a recent article in The Journal of steroid biochemistry and molecular biology (B. Gilchrest, March 2007),

Ultraviolet (UV) radiation is a proven carcinogen, responsible for more than half of all human malignancies. It also compromises skin appearance and function. Since the UV action spectra for DNA damage, skin cancer and Vitamin D(3) (vit D) photosynthesis are identical and vit D is readily available from oral supplements, why has sun protection become controversial, now that some data suggest conventionally "sufficient" levels of vit D may be less than optimal for at least some population groups? First, the media and apparently some researchers are hungry for a new message. Nevertheless, after 50 years, UV exposure is still a major avoidable health hazard. Second, the controversy is fueled by a powerful special interest group: the indoor tanning industry. They target not the frail elderly or inner-city ethnic minorities, groups for whom evidence of vit D insufficiency is strongest, but rather fair-skinned teenagers and young adults, those at highest risk of UV photodamage. Third, evolution does not keep pace with civilization. When nature gave man the appealing capacity for vit D photosynthesis, the expected lifespan was far less than 40 years. Long-term photodamage was not a concern, and vit D was not available at the corner store. The medical community should avoid sensationalism and instead rigorously explore possible cause-and-effect relationships between vit D status and specific diseases while advocating the safest possible means of assuring vit D sufficiency.

Re:We are Caucasians.

[lawpoop]

We are Caucasians. Our white skin color comes from the Caucasus mountains, north of Iran.

Are you saying that all 'white' people alive today derive their white features from an ancestor in the caucus mountains? That was a popular theory from about 50-100 years ago, but I haven't heard of any researcher that sticks by that today. Yes, there are white people in the caucus mountains, but there's no evidence to believe that white skin developed there, over and above any other place in Europe.

Here's his published research

[nbauman]

The "conflict of interest" doesn't bother me, but the lack of a link to or citation of a published study does. Does anyone know where the real details about this study are available?

They're not. That's the problem, he's talking to a newspaper without having published anything. AFA I can tell from the article, he hasn't even presented his results as an abstract or a talk at a meeting. And the Globe & Mail is usually pretty good on reporting medicine, but this story doesn't even mention whether it's a prospective, randomized controlled study or a retrospective, backwards-looking study. (And it doesn't get a reacton from another scientist who knows the research.) Apparently it's a retrospective study, which has problems. Retrospective studies found that women who took hormone replacement therapy had fewer heart attacks. But prospective studies found out the truth, which is that they had more heart attacks. The probable reason: Women who have generally healthier habits, like exercise, diet, and no smoking, are also more likely to take (useless and dangerous) hormone replacement therapy, and vitamins.

Here's Veith's earlier work, which was a retrospective study, and toned down by a responsible journal editor. As far as I could tell from a Google search, he hasn't done any prospective studies.

http://cebp.aacrjournals.org/cgi/content/abstract/ 16/3/422 [aacrjournals.org]

Cancer Epidemiol Biomarkers Prev. 2007 Mar;16(3):422-9.

Vitamin D and Reduced Risk of Breast Cancer: A Population-Based Case-Control Study Julia A. Knight1, Maia Lesosky1, Heidi Barnett1, Janet M. Raboud1 and Reinhold Vieth2

1 Prosserman Centre for Health Research, Samuel Lunenfeld Research Institute and 2 Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada

Requests for reprints: Julia A. Knight, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 60 Murray Street, Box 18, Toronto, Ontario, Canada M5T 3L9. Phone: [phone]; Fax: [phone]. E-mail: [e-mail]

Background: Vitamin D, antiproliferative and proapoptotic in breast cancer cell lines, can reduce the development of mammary tumors in carcinogen-exposed rats. Current evidence in humans is limited with some suggestion that vitamin D-related factors may reduce the risk of breast cancer. We conducted a population-based case-control study to assess the evidence for a relationship between sources of vitamin D and breast cancer risk.

Methods: Women with newly diagnosed invasive breast cancer were identified from the Ontario Cancer Registry. Women without breast cancer were identified through randomly selected residential telephone numbers. Telephone interviews were completed for 972 cases and 1,135 controls. Odds ratios (OR) and 95% confidence intervals (CI) for vitamin D-related variables were estimated using unconditional logistic regression with adjustment for potential confounders.

Results: Reduced breast cancer risks were associated with increasing sun exposure from ages 10 to 19 (e.g., OR, 0.65; 95% CI, 0.50-0.85 for the highest quartile of outdoor activities versus the lowest; P for trend = 0.0006). Reduced risk was also associated with cod liver oil use (OR, 0.76; 95% CI, 0.62-0.92) and increasing milk consumption (OR, 0.62 95% CI 0.45-0.86 for ?10 glasses per week versus none; P for trend = 0.0004). There was weaker evidence for associations from ages 20 to 29 and no evidence for ages 45 to 54.

Conclusion: We found strong evidence to support the hypothesis that vitamin D could help prevent breast cancer. However, our results suggest that exposure earlier in life, particularly during breast development, maybe most relevant. These results should be confirmed. (Cancer Epidemiol Biomarkers Prev 2007;16(3):422-9)

Re:now the counter argument... ?

[AxelBoldt]

when taken in its normal form it requires activation by UV in the skin.

That is crap. You can either take in D2 (from plants or fungi) or D3 (from animal sources) or you can produce your own D3 from sunlight and cholesterol. All these are converted by the liver into the active from of vitamin D, Calcitriol.

Not insightful, outright wrong

[BeanThere]

Several counter-points:

- Southern and particularly South Africa are HOT, very hot, and it's sunny almost every day of the year. Summer is baking hot for months. Rudimentary research would've turned that up.

- The black people of South Africa are here as a result of a relatively recent massive migration of the Bantu peoples from around the Cameroon area that spread first East and then South. In South Africa they have been here probably not more than 1500 years.

- The indigenous people of South Africa that have been here for a long time (10,000+ years), e.g. the Khoesan, DO in fact have lighter complexions than the Bantu peoples that came from the equatorial regions.

- Even the 'black' people of South Africa ARE in fact lighter than their self-same relatives from up North - in fact generally speaking the closer you get to the equator, the darker the black people get. (That itself appears to be another strong argument for the Vitamin D correlation, although it's not that cut and dry because some, or perhaps much, of the lightening of the blacks in South Africa is due to generations of interbreeding with e.g. Khoesan peoples.)

Forget about cancer -- other symptoms

[Somnus]

I have Vitamin D deficiency [wikipedia.org], and it came close to ruining my life. I am a scientist, but I also have dark skin that never burns. Even though I don't own a car, I just can't get the 2-3 hours of sunshine daily needed to fulfill my Vitamin D requirement; white folks only need 20 minutes. Moreover, it's kind of chilly where I live, so I wear long pants and sleeves much of the time.

Over time, I developed a pain that just sucked the life out of me -- like I was playing four quarters of football daily, with the flu. Even with powerful pain killers I couldn't sleep, and woke up every day feeling I was hit by a bus.

The link to cancer is still an open question, but the pain is a hard fact [mayoclinic...edings.com].

PS: The only way to overdose on Vitamin D is to abuse prescription-strength supplements or cod liver oil.

Re:60% reduction in risk?

[Octopus]

Like all things, the Vitamin D issue is only one component - there's also:

• Oxygenation - studies have shown cancer cells thrive in parts of the body where there is low oxygen. Hence the current studies with hyperbaric oxygenation chambers, and the flushing the body with O2. How this is relevant to modern life and the cancers we get, I'm not sure - it may have to do with sedentary lifestyles, air quality, diet, or all of the above.
• Acidity vs Alkalinity in the body - this is why broccoli and other legumes become known for preventing cancer. A better understanding of the acid/alkaline balances in our body is reportedly key as well - many people actively check to find out where they're at. Another diet and activity issue.
• EM fields - we've all heard the stories about living near power lines, etc. I'm sure this is a mixture of valid science and a handful of Luddite hysteria, but low-frequency EM rad is still a little suspect.

And now that I'm blabbing about this off the top of my head, I'm sure I'll be beaten in the street for yakking about science I don't understand.

Re:Actually I can a dark colored race in the north

[AaronStJ]

Your couple of anecdotal examples aside, the major trend in clearly towards darker skin nearer the equator. Look at any of the countless skin color maps [wikipedia.org] that researchers have generated.

Re:Actually I can a dark colored race in the north

[joto]

So what happened to the folks from Iceland and Scandinavia? These folks eat fish to the wahzoo and some of it is downright disgusting.

Oh, are we? I didn't know that. Like most norwegians, I very rarely eat fish. However, Norwegians fish a lot of fish, which is exported to other countries.

In a historical perspective, it's no different. While many coastal-living norwegians has had fish as an important part of their diet, it has never been like the inuits who practically eat nothing but fish and seal. Farming has probably been even more important. And people would trade, so farmers would get fish, and fishermen would get meat, grains (rye, oat, barley), root vegetables, and other herbs).

Re:now the counter argument... ?

[iamplupp]

Well actually it is converted to 25-OH-vitamin D in the liver. And that in turn gets converted to calcitriol in the kidney.