Vitamin D: the “Sunshine” Vitamin


Rickets is a disease of the bones which affects
children and is caused by insufficient bone mineralization during growth: as a result,
bones weaken and bow under the body weight’s pressure. Before the seventeenth century, rickets was
an almost unknown disease. But soon after the industrial revolution,
with its huge problems of pollution in urban areas, the incidence of this disease skyrocketed. It took scientists almost two centuries to
figure out that the two things were connected: somehow, it was exposure to sunlight that
was able to prevent the onset of rickets. Towards the beginning of the twentieth century,
scientists realized that if a child with rickets is exposed to the light of a UV lamp, the
disease will regress. It was clear however that light did not act
directly on bones, because when a child was exposed to the UV light on just one arm, the
disease regressed in the same way in the other arm as well. Clearly, exposure to sunlight, or the light
of a UV lamp, was able to induce in the skin the production of an anti-ricket element,
that could subsequently be carried to the rest of the body. Unfortunately, the levels of air pollution
following the industrial revolution were so high that the smoke generated from the factories
would filter most of the light coming from the sun, especially in urban areas, causing
the above mentioned spike in rickets cases in children. Nevertheless, a winning strategy to cure rickets
had already been discovered one century before by professor Bretonneau, and had nothing to
do with sunlight. Rather, it was cod liver oil. When administered to ricket patients, it caused
the disease to disappear, incredibly fast. How was it possible that two so different
strategies – exposure to sunlight or eating a fish oil – were both able to independently
cure rickets? It wasn’t until 1920 that scientists were
able to figure it out, by identifying the wonder molecule that’s contained in cod
liver oil: it was called vitamin D, or colecalciferol. This very same molecule is also the “antiricket
element” that is built in our own skin when it is exposed to sunlight. But if a deficiency of vitamin D in children
seriously impairs mineralization or the growing bones, resulting in rickets, it is just as
detrimental in adults and even more in older adults, causing a painful reduction in bone
mineralization, called osteomalacia, as well as promoting ostheoporosis, a weakening of
bone mineral structures that make them extremely fragile and prone to fractures. For the same reason, many people suffer from
seasonal back pains, joints and muscle pains, often confused with arthritis. Oftentimes, a vitamin D supplement would be
enough to make these ailments go away. But why is vitamin D so important for the
health of our bones? The main task of vitamin D is maintaining
adequate concentrations of calcium and phosphorous in our bloodstream, which in turn ensures
an adequate supply for the mineralization of our bones. Vitamin D accomplishes that in two different
ways: first, by regulating gene expression in our intestine, it stimulates the production
of those proteins that are necessary to absorb calcium. In other words, vitamin D promotes calcium
absorption from food. Second, in our kidneys, vitamin D stimulates
reabsorption of calcium and phosphorous, preventing them from being lost with our urine. These two mechanisms all result in the same
effect: our blood concentrations of calcium and phosphorous raise. Keeping their concentrations stable is vital
for our own survival, as they are necessary so our heart can beat and nerve impulses can
be transmitted. Of course, vitamin D is necessary only when
blood levels of calcium and phosphorous are low, but we don’t have to worry about that. Vitamin D by itself is inactive. When it is necessary, our body takes the necessary
steps to activate it so it can become an active hormone, called calcitriol, and perform its
important functions. Active vitamin D is so powerful that its activation
is very strictly regulated, and it needs two different consecutive steps, as if you needed
two different keys to open a safe box. The first activation step takes place in our
liver, the second in our kidneys. This means that getting plenty of vitamin
D from food, sunlight exposure or supplements, does not automatically result in inducing
its hormonal activity if that is not necessary. It just means giving our body the opportunity
of doing so, should the need arise. But vitamin D is not just important for calcium
absorption and the health of our bones. Vitamin D is an amazing molecule that never
ends to surprise researchers. It is a hot topic in nutrition, it is still
actively researched, and we keep finding out more and more fascinating things about this
powerful molecule. First of all, active vitamin D has a very
strong anti-cancer activity, by inhibiting cell proliferation and promoting cell differentiation. Numerous epidemiological studies have associated
low vitamin D with increased incidence of cancers, especially breast, colon, prostate
and ovaries cancers. Vitamin D exerts an important regulatory activity
on our immune system and its deficiency has been associated to increased risk for autoimmune
disease, including type I diabetes and multiple sclerosis. So far, we have identified about fifty genes
whose expression is regulated by vitamin D. A few years ago, it has attracted a lot of
interest the role of vitamin D in raising serotonin levels, which improve our mood,
thus making it a sort of natural antidepressant. During menopause, vitamin D and calcium supplements
are often beneficial in controlling some of the unpleasant symptoms, such as hot flashes
and irritability. By inhibiting excessive secretion of renin
from our kidneys, vitamin D also help control blood pressure and avoid hypertension of renal
origin. Marginal deficiencies of vitamin D have been
associated with increased risk for acute cardiovascular events, such as heart attacks and strokes. The list could go on and on, but I think I
gave you an idea of how many different things this powerful molecule can accomplish. Food sources of vitamin D are rather limited. Short of eating fish liver oil, the best source
is eating small fishes that you can eat whole, including their livers, such as sardines. Fatty fish, such as salmon or herrings, also
have more vitamin D because they store some in their adipose tissue. The only known significant vegetable source
of vitamin D are sun-dried mushrooms. Apart from these sources, the only relevant
food sources of vitamin D are fortified foods. In the US, all milk and many brands of orange
juice are fortified with vitamin D. Breakfast cereals are also often fortified with vitamin
D. But vitamin D is not strictly essential as
a nutrient, because like we said, we can build it ourselves in our skin, starting for cholesterol. To do that, however, we need our skin to be
exposed to a source of UV light, typically sunlight. However recommending to increase sunlight
exposure to maximize vitamin D synthesis poses the problem of skin cancer prevention, as
UV radiations that activate vitamin D production are the same involved in skin ageing and oxidation. Unfortunately, using a sunscreen protection
will abolish vitamin D production as well. However, it’s important to remember that
you don’t need a whole lot of sun exposure to maximize vitamin D production: you only
need 5 to 15 minutes of sunlight exposure two to three times a week, depending on how
dark your skin is, and exposing your face, arms and hands is enough to cover your vitamin
D needs, although if you can expose your legs as well, that’s even better. After that initial exposure, vitamin D will
actually start being broken down to avoid excessive accumulation, so if you need to
stay out in the sunlight for longer, you can go ahead and use your sunscreen to protect
the skin without worrying for vitamin D. Unfortunately, for many people and in many
areas of the planet, even a ten minutes sunlight exposure a few times a week isn’t feasible
the year round. Those living at high latitudes, where it’s
dark for many months a year and often weeks go by without sun at all, are at extremely
high risk for vitamin D deficiencies, as well as those individuals that – although living
in sunnier areas – spend most of their times inside buildings or in their car, or they
go out wearing clothes that cover most of their skin. People living in highly air polluted areas,
are at risk because particles in the air filter UV light. Finally, black people living at non equatorial
latitudes, are at risk even if they expose themselves to sunlight because their skin
needs much more UV light to make vitamin D. For epidemiologist Julian Peto, the reason
why early humans moving north evolved to turn their skin white, is precisely because more
vitamin D enhanced their survival. For all these people at risk, it is highly
recommended, at list during the winter months, the use of vitamin D fortified foods or of
a vitamin D supplement. The RDA for vitamin D is set at 15 µg until
70 years of age, and 20 µg after 70 years of age, as the skin ability to make vitamin
D decreases with age. These levels however are based on the amount
needed to maintain bone health and normal calcium metabolism, and do not take into account
the many other benefit of vitamin D. Many nutritionists, following the recommendation
of the prestigious micronutrient center of the Linus Pauling Institute, advise all healthy
adults to get a higher daily amount of vitamin D, of 50 µg, through supplementation if necessary. To the best of our knowledge, this level poses
no risk of toxicity and can only improve our health status. Finally, let me spend a few words on cod liver
oil, which is the richest natural supplement of vitamins A and D. Although many think of
it as a disgusting concoction, well stored cod liver oil has just a slight taste of fish
if eaten as such, but most supplements are available in the form of coated capsules that
can be swallowed without having to ‘taste’ it at all, and without living any fishy aftertaste
in your mouth. You should get it after the most abundant
meal of the day, so that you have enough fat to efficiently absorb all the fat soluble
vitamins, and together with a multivitamin multi mineral supplement that will also provide
some calcium, to keep our vitamin D busy, as well as vitamin E to prevent fat oxidation. It must be stored in the fridge, or in a cool,
dark place to prevent rancidity and vitamin D degradation. Finally, be very careful not to exceed the
recommended dose, because as you have learned, both vitamins A and D can easily accumulate
and become toxic if we get too much!

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6 thoughts on “Vitamin D: the “Sunshine” Vitamin

  1. Ohhhhh finalmente…. aspettavo con ansia la nuova puntata :)…. interessante la questione dei funghi esposti al sole or uv lamp per un'orettina, in tal modo ricchissimi di vitamina D….

  2. Hi, it´s just to point out that this video hasn´t been included into the playlist 7. Keep on the outstanding course, Vasco

  3. Many thanks for this amazing presentation! Would you raccomand the use of big doses of supplement even during the summer? Could be enough taking 5-10μg per day, if regularly exposed to sun?

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