White skin itself is an evolutionary adaption for getting enough vitamin D outside of tropical Africa. The extreme "melanin-anemic" blond & blue eyes look of Scandinavia is thought to be because it has a uniquely warm weather for the latitude, which make it possible to grow (vitamin D poor) grains there. That supports by far the biggest population density that far north, but also induces extreme whiteness to soak up every possible sun ray.
Conversely, if you have dark skin and live in the non tropics, you absolutely need to monitor and enhance your vitamin D intake. Sadly, doctors don't seem to bring this up with dark skinned patients, at least from what I hear from my (OK, not that many...) black friends.
- Scandinavia is very far north and therefore gets less sun in the winter (obviously)
- Apparently the soil of Scandinavia is well suited to crops that are high in Vitamin D
The soil being good for Vitamin D crops (plus lightening of skin/hair and fish diets etc) was a part of why people were able to live in such far northern climates even if they didn't always have access to fish.
IIUC it's the other way around. soil/climate allows for foods low in Vitamin D -> Vitamin D needed from other sources -> evolutionary pressure for getting it from the sun -> less melanin in skin
Some fungi have decent vitamin D, but it's certainly not a major "crop" in Scandinavia.
"White" and "dark" refer to the skin's effects on visible light. Visible light is different wavelengths from UV light; vitamin D production in the skin depends on UV light. "Dark" skin blocks UV light more than "white" skin does.
I think this is how it works: The melanin is not transparent, so it stops the light from penetrating beyond the very surface, and so a smaller volume of skin cells get access to sunlight.
To go a little deeper: Sunlight does two major things in our skin. It creates vitamin D, and destroys folate. Both are essential, so the various skin colors we have reflect the balance evolution has struck in various environments.
Incidentally you can test this yourself: if you go out in the summer you will tan i.e. your skin will darken. This is adaptation to lower the risk of sunburn and skin cancer.
If you could design a human from scratch, it might be most efficient to give northerners a D synthesizing pigment that's opaque in the necessary wavelength, resulting in the situation you describe.
Instead we have protective pigments near the surface, synthesizing structures underneath, and a need to balance D synthesis against UV damage.
Sure, some photons do get reflected, but the benefit is from those photons that get deeper into the skin.
At the end of the day I don't know enough, so I'm not making the claim about Vitamin D quantities, but isn't the evidence that there was at least some form of adaptation evident based upon skin tone alone?
I agree. Don't overdo it though, 5000 IU daily seems a bit much :) I live in Amsterdam and take 2000.
1: https://www.medscape.com/viewarticle/744128 2: https://www.ncbi.nlm.nih.gov/m/pubmed/28768407/
I think it depends on the person. If you get your blood level checked when you have a regular physical, you can adjust the dose as needed to keep the level where you want it (I shoot for the upper end of the normal range, and 5000 IU a day seems to be doing that for me).
2000 IU a day, 3-5 days a week. Not strict about it, just whenever I remember. Big difference in terms of energy, depression, sleep quality, etc.
I've messed around with higher levels but they usually give me wicked headaches.
You can probably play around with the brands and doses a little. I think the important thing is to take gel capsules with oil inside and not solid pills. Vitamin D is fat-soluble so I think solid pills don't get absorbed very well.
Most articles I have read recommend somewhere between 2000 and 5000 IUs. Some recommend higher.
I wonder what the actual numbers are for this. This weekend, I got out for a couple of 3 hour bike rides, for instance, but it was chilly out, so nothing but my face was exposed.
7-dehydrocholesterol --(UVB @ 296nm)--> previtamin-D --(thermal isomerization)--> cholecalciferol
The first step reaches equilibrium after about 15 minutes in Fitzpatrick type 1 skin in UV index 3-5 (moderate), and about 2 hours in Fitzpatrick type 6. The total amount produced is dependent on the surface area of exposed skin, and the previtamin isomerizes slowly, over about 12 days.
Time to equilibrium is about half the time to acquire sunburn at a UV index high enough to catalyze the previtamin-D reaction. At UV index 6-7 (high), time to burn is about the same as the time to reach previtamin-D equilibrium. At UV index 8 or higher (very high), you will burn faster than you make previtamin-D, and should maybe avoid being exposed during the midday hours. At UV index 11 or higher (extreme), if you are Fitzpatrick type 1, you will carbonize to a burnt matchstick the instant you step out of shadow, like a cartoon vampire, and you should not only not be outside, but should also be huddling in a dark basement waiting on the tyranny of the sun to pass.
Thanks to the equilibrium in the skin, the maximum absorbed dose from sunlight is the equivalent of about 20000 IU per day. High vitamin-D intake also requires increased vitamin-K consumption to reduce calcification of soft tissues.
Even that might not be enough, since in many people the body's ability to synthesize vitamin D when exposed to sunlight decreases with age. The only way to know for sure where you stand is to get your blood levels checked when you get a physical, and supplement if you need to.
This sort of thing is impossible to diagnose correctly without lab tests.
Our modern diets could cause further nutritional deficiencies. I doubt that many people in the West eat fish regularly or supplement with algae oil due to the conveniences of processed food. Same with iodine. Wheat germs have the highest concentrations in vitamin B1, but whole grains in general (rolled oats etc.) are good so you should probably cut the processed food out as much as possible.
My doctor recommends all his patients supplement with B12, regardless of whether they're vegetarian, because of the above mentioned potential for everyone to have B12 deficiency, and, according to him, tests for B12 aren't reliable.
Pretty sure that's the reason almost all milk in the USA is fortified with Vitamin D (and A)
Depends on your own skin color too.
The biggest effect anything I had on me is Testosterone Enthante 250mg twice a week.
Also I wonder if taking 8,000 IU vitamin D can desentivize the system overtime
No you can't. That's not how this works.
Yes I can :D
While my experience is obviously not definitive scientific proof it can still bring some value.
To give you a more simple example: when I broke my leg I went to the doctor's and put it in a cast. That helped me tremendously. Is that a well designed randomized controlled trial? No. Is it good advice to anybody with a broken leg? I would say so.
The setup you describe is for proving (with some statistical certainty) a certain causal relationship.
But the author doesn't want to prove it. It has already been proven experimentally. What he said is that he can tell us from his own experience. You don't need a controlled study for that.
I can tell from experience that a certain vitamin X deficiency can be very bad (e.g. because I had it, my doctor verified it, and I got very sick and had Y symptoms) without needing to prove that vitamin X causes Y if it's already proven.
Which is the same case with vitamin D. The parent didn't say he'll prove something novel, just that they'll verify it from experience.
Note that verification from experience is still very useful, even when something isn't proven. It's not as rigorous as science, but it's still very useful, can be life-saving, and it's how civilisation advanced for 1000s of years before we got "controlled studies". People already knew from experience not to eat X or Y plant for example (e.g. poisonous), without official studies and control groups.
People should still be required to be able to make deductions and learn from experience at this level before they offload everything to scientists.
I suspect that essentially all people living at relatively northern latitudes have some sort of vitamin D deficiency. From what I know you need to have your face and arms exposed to direct sunshine for at least 15 minutes/day to keep healthy vitamin D levels in the body. Good luck with that in the European/Canadian/Northern US winter.