Vitamin D Deficiency: A Major Health Side effect of Human Migration

More than just bones!

pile of human skulls
Photo by Felipe Hueb on

Vitamin D may be our most important ‘vitamin’. Although it has long been known that Vitamin D plays a critical role in the body’s ability to absorb and retain calcium and phosphorus, which are both critical for the formation of bone, recent research has now revealed that Vitamin D plays critical roles in the control of infections, in mental health and in the reduction or perhaps prevention of cancer.

I personally became aware of the probable role of Vitamin D in mental health when I noticed that several of our darker-skinned Indian students were becoming seriously depressed during South Australian winters. When I discovered this, I suggested that they took some Vitamin D rather than the anti-depressive drugs they had been prescribed but I didn’t realize then that Vitamin D deficiency might be associated with major depressive and anxiety disorders.

People migrating

Major increase in worldwide Vitamin D deficiency caused by modern lifestyles and migration

Vitamin D deficiency is present in millions of people throughout the world. Some of this is due to changes in lifestyle where people spend a great deal more time indoors than they ever did before. This overall alteration in behavior has many causes that include loss of traditional types of work, innovation, and mechanization of transport such that walking is less of a necessity, modifications in buildings that encourage more time to be spent indoors and general loss of traditional lifestyles


Under our most natural environments, that is living in the region of the world where our ancestors evolved, our skin color should be adapted to allow it to synthesize adequate amounts of Vitamin D, when it is exposed to sunlight. Those of us whose ancestors lived far away from the equator generally have pale skin with low amounts of the pigment melanin whilst those who evolved to live near the equator have much darker skin, with higher concentrations of melanin.

One apparent exception to this is the Eskimos or Inuits. This race of people initially originated in Asia from where they migrated. In their new home Alaska in the frozen north, they adopted a diet of raw fish and sea animals, the meat of which is exceptionally high in Vitamin D. Their practice of eating the food raw also insured that they had sufficient intake of Vitamin C.

Skin Cancer

White skinned people moving to latitudes with higher amounts of sunshine, can do well in terms of producing Vitamin D in the sun but there is a significant trade-off in the form of sunburn and skin cancer. The good news is that the studies that have been undertaken on sunscreens to date do NOT show that wearing sunscreens prevents our skin from manufacturing Vitamin D. However – be cautious – studies have not yet been undertaken on the sunscreens offering very high levels of protection!

People with black skin can still develop Melanoma but not too surprisingly, white-skinned people are 25 times more likely to suffer from it. But Melanoma is relatively rare compared to other types of Skin Cancer of which there are well in excess of a million diagnoses each year worldwide, mostly in people with lighter skin.

Dark-skinned people living in countries with less sunlight

‘Pre-vitamin D’ or its full name 7-dehydrocholesterol (7-DHC) is a chemical that has been conserved through animal evolution. It is produced as part of the synthesis of cholesterol and with the help of sunlight it is converted to Vitamin D3 (cholecalciferol) in the skin. Vitamin D should probably be regarded as a pro-hormone rather than a ‘vitamin’ because of its diverse biological roles and its evolutionary role in insect metamorphosis.

Vitamin D synthesis is highly influenced by the concentration of melanin in the skin. Melanin actually absorbs and then scatters the Ultra Violet (UV) ‘B’ rays and the this results in far less efficient conversion of pre-vitamin D to D3. Consequently, dark-skinned people synthesize vitamin D far more slowly than lighter-skinned people and need more time in the sun to produce equivalent amounts of this critical vitamin.

Ageing reduces Vitamin D production

Thin aged skin and joint deformity – common signs of aging

Not surprisingly, clothing inhibits the production of Vitamin D in the same way that it protects against sunburn but what is not so well known is that ageing also decreases our ability to produce Vitamin D. Aging affects the production in two ways. It both reduces the synthesis through the skin in sunlight by about half and then there is probably a further decline in the renal production of the active hormone! So, as you age, you either need to spend a lot more time in the sun making your Vitamin D or you need to eat Vitamin D rich foods or take a supplement.

If you have sufficient intake of Vitamin D, you can expect to have stronger bones, heightened immunity, less risk of cancer as well as feeling much happier. But this might not be all the advantages? The fact that almost all cells in our bodies have what are called Vitamin D ‘receptors’. This means that Vitamin D plays at least some role in all our cells!

You might also enjoy watching my YouTube video for some more information about Vitamin D: Vitamin D and 14 health benefits

Can eating Seaweed prevent Breast Cancer?

asia carrot chopsticks delicious

In Japan, seaweed is a common dietary component which gives Japanese adults an average daily intake of 5280 micrograms (µg) of Iodine each day. This is very different to the rest of the world where the average intake of Iodine is only about 209 µg/day. Now there are obviously other dietary differences between traditional Japanese people and the rest of the world, not to mention many lifestyle and cultural differences, but could eating seaweed, and in particular consuming relatively high amounts of Iodine, be an important protective factor against breast cancer?

You can see in the following figure whose data has been taken from a collaborative study between Australian and Japanese researchers, published in 2020[i] that although the rate of breast cancer has increased dramatically in both countries between 2006 and 2015, that the age-specific rates are approximately double in Australia when compared with Japan.

Breast Cancer rates in Japan & Australia in 2006 and 2015

It’s likely that you know about the importance of Iodine to the health of the Thyroid gland. You might even be aware of the pioneering work in public health performed by the Australian Dr Basil Hetzel (1922-2017), who improved thyroid health worldwide through the addition of Iodine to household salt. I was lucky enough to know Basil as a colleague and friend and I’m sure he would have been extremely excited to know that Iodine’s critical roles are not just limited to the thyroid but that it also has important roles outside the thyroid gland as an ANTIOXIDANT, DIFFERENTIATION FACTOR AND IMMUNE MODULATOR [ii]  However, there is a major difference in the chemical form of Iodine that is critical to thyroid function with that in cancer prevention: The thyroid gland uses ‘Iodide’ salts whereas cancer suppression occurs with ‘elemental Iodine’. In fact, elemental Iodine probably plays a preventative role against all cancers, but few have been studied. Nevertheless, there are several well-controlled scientific studies that demonstrate Iodine’s role in controlling breast cancer.

The studies on Iodine and cancer prevention are mostly very new and it will probably be a long time, if ever, before we see Iodine being recommended as a ‘cancer cure’. Furthermore, there is other strong evidence that Iodine itself is not enough! For example, in a well-designed ‘prospective’ Italian study, the researchers found that Iodine intake alone did not reduce breast cancer risk and that Iodine needed to be combined with adequate Selenium to be effective. Indeed, women who had intakes of each of Iodine and Selenium that were above average, reduced their breast cancer risk by at least 25%. This supports an hypothesis linking Iodine and Selenium to cancer prevention that was first proposed in 2000[iii].

The study result fits with the protection offered against breast cancer by dietary seaweed because seaweed is high in both Iodine and Selenium, and it also fits what is known about the biochemistry of Iodine in the breast in that it requires the activity of Selenium-dependent enzymes for its function. Selenium is indeed a very important trace element that is essential to the function of several of our critical ‘defense enzymes’ in most cells. But – a WARNING – it must always be remembered that Selenium is a ‘trace element’ and too much is as bad as or worse than too little! 

Another nutrient that is strongly associated with breast cancer is Vitamin D. Almost all studies show that higher levels of Vitamin D confer a lower risk of breast cancer and you’ve probably guessed that seaweed is a nutritional source of Vitamin D – although you probably need more than you will consume in your seaweed! You can synthesize your own Vitamin D very effectively from sunshine (when your skin is exposed to it) but nowadays because of the number of hours most of us spend indoors together with our use of sunscreen and clothing to protect ourselves against skin cancer, most of us are deficient in Vitamin D (for some or all the year). Having a dietary source of Vitamin D or taking a supplement is thus often necessary.

How does Vitamin D intake fit with Iodine and Selenium? Well, without going into the details there is plenty of biochemical evidence to show that Vitamin D plays a role in ‘up-regulating’ the Selenium-dependent enzymes that are involved in many defense and scavenging activities in our cells. So, although there is some Vitamin D in seaweed, sufficient Vitamin D is important to in addition to the protection offered by Iodine and Selenium.


Take-home message! Either eat seaweed on a regular basis or find other reliable sources of Iodine and Selenium and make sure your intake of Vitamin D is sufficient. I strongly suggest that if you are intending to eat seaweed on a regular basis that you research your seaweeds carefully. Different seaweeds contain very different amounts of Iodine and Selenium and you do want to make sure you have the ‘goldilocks’ amounts – not too little and just as importantly not too much!

[i] Mizukoshi MM et al (2020) Comparative analyses of breast cancer incidence rates between Australia and Japan. Asian Pacific J of Cancer Prevention 7: 2123-2129

[ii] Acerves C et al (2021) Molecular Iodine has extrathyroidal effects as an Antioxidant, Differentiator and Immunomodulator. Intl J of Molecular Sciences 22: 1228-1243

[iii] Cann SA et al (2000) Hypothesis: iodine, selenium and the development of breast cancer. Cancer Causes Control 11: 121-127

Our genes and our diet

Vegetarian, omnivore, carnivore, pescatarian – which is the correct diet and what does logic, our genes and our anatomy tell us?

Suppose you came across an object you’d never seen before, and you wanted to work out its purpose? What would you do? I think most people would look at its general construction and ask questions such as:

  • How is this object constructed and of what materials?
  • What are its major parts?
  • What are its most likely functions?
  • Where in the world did it originate? If its location is/has been changed, does it need or has it needed some special adaptations to adapt to its new location?

If we applied these questions to ourselves, we might more readily understand how to differentiate between the accurate and vastly inaccurate so-called ‘health information’ that is readily available today. Clearly this is an enormous topic so to start I just want to focus on the most basic elements of diet and on the role of the head. I will address many specific sub-topics in the coming weeks.

Today’s question: What can we learn about our diet from our heads?

The construct of the HEAD

ONE HEAD has the five major organs brain, ears, eyes, nose, and mouth. The most notable moving parts are the eyes, which allow us to see food and the jaw which allows us to bite and chew food.

Each organ of our entire body, and the head is no exception, is composed of nerve, blood, bone, and skin cells (of which some are external and some internal). There are also specialized structures in the mouth called teeth, which are composed of enamel and unlike bone, do not contain living (potentially replacement) cells as bone does. The mouth also contains another specialized muscular organ, the tongue, that is vital for taste, chewing and swallowing as well as creating sounds, especially speech.

From an evolutionary perspective, almost every part of the head has played an essential role in nutrition. The eyes, ears and nose have allowed us to detect the presence of potential food and after we hunted or gathered our tasty morsels, our tongue and teeth then allowed us to eat it. However, since relatively few of us have been involved in food gathering and/or production for some generations, our teeth may be our foremost guide to the foods that best suit us today.

Our incisors (eight – four in the upper and four in the lower jaw) are in the middle of the front of our mouths and each has a flat edge that is adapted for shearing and cutting food. Being in such a prominent position, this may be the most important function.

Our canines or cuspids (four – one on the jaw side of each pair of incisors) have a sharp edge and are for tearing food.

Our pre-molars (eight – two pairs in the upper and lower jaw on each side) have flat surfaces with ridges for crushing and grinding food into smaller pieces to make it easier to swallow.

Our molars (twelve – three pairs, upper and lower on each side of the jaw) have a large surface that helps them to grind food.

What our HEADS would lead us to conclude about our diet?

It’s not necessarily logical to conclude that because we have such a high proportion of our teeth adapted for crushing and grinding food that crushing and grinding should be our primary dental activity. Nevertheless, I think that the very large number of grinding teeth attests to the fact that some types of plant-based diet has been consumed by humans over most if not all their ancestry. Furthermore, the high proportion of this type of tooth strongly supports this ancestry and plants should form a major proportion of our diets.

Nevertheless, the presence of canine teeth, which are in a very prominent position strongly suggest that cutting and tearing teeth are still required by humans and that foods, such as animal flesh that require cutting and tearing should also be part of our healthy diets.

Chimpanzee and Human Diets

Our DNA is only 1.2% dissimilar to the Chimpanzee and it’s logical to think that our dietary adaptations might be similar. Chimpanzee in the wild have a diet that is mostly vegetable/fruit and not surprisingly always those that are in season! They are now known to dig up small crustaceans from mud, to eat insects and to hunt and kill smaller monkeys, whose flesh they eat. So, meat forms only about 3% of their diet in the wild and is eaten on only about 9 days each year.

Taken together these facts suggest that humans have evolved to eat some meat and crustaceans but mostly a diet of fruit and vegetables. However, these facts don’t tell us which dietary proportions are optimal and in the coming blogs we are going to move past the head to try to piece the facts together!

So, till next time ……….

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