Probably the best post so far. Pretty accurate too.
I researched Vitamin D3 at various levels from 2009-2014.....while checking my blood levels (ng/ml) up to twice a year. At that time I was also testing my body inflammation via C Reactive Protein and Homocysteine. Read half a dozen books on the subject. I did full body sun-tanning outdoors in summer, D3 supplements, and even the tanning booth (I know....God forbid). But I certainly found out how my D3 levels (and health) changed and probably why. I was aged 55 to 60 during that period, so my absorption of Vit D could have been weakened by my age. But my blood levels indicated levels responded well to what I was doing. I was able to convince my Doctor back then to get the extra tests. These days, doctors don't want to do anything "extra," unless it's on your dime. My basic conclusions:
The RDA of 20-30 ng/ml Vit D3 prevents rickets. That's it. It's not for maintaining minimal or even good health. Doctors might cite 30 ng/ml as adequate but it's not for best health either. Most studies I've seen require 40-60 ng/ml for proper health. As I recall Africans along the equator were often in the 40-50 range just from their daily activities in the sun year round. The further North or South of the equator you live, the less UVB rays you see, and the lower Vit D3 levels you will tend to have. As I recall UV rays are 95% UVA and only 5% UVB. It's UVB we need for D3. You can't get UVB w/o UVA exposure. The UVA rays are there all year round. And the UVB rays get attenuated fairly easily just by cloud cover. I would also note that when I did do tanning beds, I ensured that the lamps they were using also mimiced the 95/5% ratio of the sun, and the same basic UV wavelength spectrum. There might be some UV bulbs out there that are 100% UVA....which won't help at all. And others with greater than 5% UVB. If you're using D3 in nmole/ml then divide by 2.5 to get ng/ml.
It's nearly impossible to over-dose on D3 via the sun....at least not w/o frying yourself to a crisp long before then. Your skin will darken over time and your levels will go down doing the same exposure time. The darker your skin the less you can absorb. You can easily get 6000-12,000 IU by 30-45 min in the sun with full body exposure (wearing only shorts and a hat). 15-30 min 3 to 4x week is probably all you need. Exposure is optimum at 1:00 PM in the USA from around mid March to mid-September. For me in New England my summer sun window is from March 28th to September 15th....it varies by Latitude. And you can check the sun's azimuth on line for your latitude (50 deg or less is too low....and angles of 60's to 70's is high). June 21st is the peak day of exposure. I prefer the hours of 12-2 pm. But 10 am to 3 pm works in peak summer but tails off on either side of June 21st. Ideally, you want the sun highest in the sky to get the most UVB rays in the shortest period of time, which are the ones that quickly form Vit D3 (cholecalciferol). The angle of the sun is important. In winter, (Oct-Feb) the Sun's angle is too low anywhere in CONUS to get usable D3....not in Miami Beach, not in Southern Texas or San Diego. So for 5-6 months out of the year you aren't getting any Vit D3 from the sun....so you will need to supplement a few weeks after your last summer dose. My blood levels would be in the 55-65 ng/ml during summer sun exposure, or in a tanning bed. On just supplements I range from 40-50 ng/ml. My wife's levels with just very modest (non-tanning) sun exposure during the summer was NEVER above 32 ng/ml. So she started supplementing at 1000-2000 IU per day....and does try to get 15-30 min of sun a few days a week in summer. Take your D3 supplement with the fattiest one or two meals of your day.
4000 IU per day is probably a decent level for good health - for a 175 lb man. Size and age could alter that in either direction. Since the general half life of D3 is approx 3 weeks on average, figure in 6-12 weeks w/o supplements or sun, you're deficient. It probably takes 1-2 months to build up your levels. For those severely deficient or at health risk, Doctor's will often do injections of 50,000 IU or more for a short period time to get you into a safe range. Once there, daily supplementation of 2000-5000 is probably needed. The RDA level of 600 IU won't get you very far....probably no higher than 30 ng/ml. Foods generally won't push you that much higher unless you eat a ton of fish or highly concentrated food sources of D3. Most of us don't. The average daily diet in the USA will not get you close during the Oct-Feb winter months. On a bio-available basis the Sun is #1. Then comes Vit D3 and then Vit D2 which is not as efficent as D3. As I recal, the body via the sun is 30-50% more efficient than taking the supplements. And food absorption is even less efficient than supplementing. The Sun was always supposed to be our main source of D3. It's by far the most efficient, and the quickest way to get it safely. Along with the dosing comings numerous photo-isomers that benefit our health....and it's not yet well understood. I spent a lot of time out in the summer sun as a kid and into my early 30's, with lots of exposure on my face, neck, arms. So when I summer tan these days, I shoot for a lot less exposure on those parts and more on my upper legs and torso.
In a nutshell, if you're not supplementing during the months of October to February in the USA, you're deficient in Vit D3 which seems to have linkage to minimimizing many auto-immune diseases, cancer, heart disease, respiratory issues, etc. Big Pharma or Big Medical has little interest in such studies as it's not in their financial interests to have you supplement. But the literature is out there if you dig around. The dermatolgists have had us cover up and lather up while avoiding the sun for the past 30 yrs. How has that worked out in preventing the rise of disease, skin cancers (or all cancers) and improving health outcomes in that time? Not very well. If you live around the equator, no need to supplement if you get some sun during the week. For those who have concerns about getting sun vs skin cancer, that's a discussion with your doctor.....you can still supplement though. I don't think there any studies out there showing any detrimental affects or toxicity from taking up to 10,000 IU per day via supplements.
The supplements aren't as effective as getting 10,000 IU from the sun. And not all supplements may work well. Personally, I started using Nature Made D3 and CoQ10 ....and got good feedback from my body that they were indeed working.....and getting absorbed. I've been on a perio-dental routine since 1990....and noticed that within a few weeks after starting CoQ10 about 10-15 yrs ago that my gums entirely stopped bleeding during flossing. It's never returned. I took that as "good" feedback. I originally took the D3 (sun and supplements) and CoQ10 for better blood pressure control. It was only a bit later that I found out about the other benefits of D3 and CoQ10. Of course none of these supplements (vits or minerals) work in isolation. And to do a proper study that mimics the proper balance of all the "important" ones is close to impossible. We just don't know it all. But D3, Ca, Mg, CoQ10, Potassium, B vitamins, selenium, copper, phosphorus, Vit A/C/E/K all play a role. For building bone Ca, D3, K2, Mg play a group role. Building bones is a good building block for proper health. And if you're going that route, it helps to have the rest of your food intake and diet be as healthy.
The only thing I'm sure of is that D3 is the one thing we are deficient in half the year. And if you avoid the sun in the summer too....you're deficient all year round, inviting in colds, flu, and other diseases and general bodily inflammation. If you doubt this, then check your D3 blood level in Jan/Feb and see where you are at. These are my own personal experiences from reading and researching. You might come up with different conclusions. Check with your doctor before altering your routines. A good place to start for research is Nutritionfacts.org.(see Vit D3 graphic below). I don't agree with everything they say there, but they have a good track record of stating well done studies. Those guys recommend 2000 IU daily....along with the Vitamin D Council. It's certainly a "safe" stance without risk.
https://nutritionfacts.org/blog/vitamin-d-recommendations-infographic/
www.ncbi.nlm.nih.gov
www.mayoclinic.org
