April 30 2020
Q: I am hearing from many doctors that "stay at home”/”lockdown” orders, parks and beach closures lead to Vitamin D deficiency because of lack of sun (ultraviolet - UV light) exposure. Is this true?
A: No, this is not correct. The main mistake is made when we assume that all Vitamin D we need is produced in our skin while exposed to the sun. in fact, 90% of Vitamin D is consumed with food and then metabolized in the liver and kidneys. Respectively, approximately 10% of PRE-Vitamin D3 is produced from 7-dehydrocholesterol in the skin under direct sunlight.
Q: I see that you measured Vitamin D 25-OH in my blood. Is this different from Vitamin D2 or D3?
A: No, we routinely measure Vitamin D 25-OH. It does not distinguish between D2 or D3 forms of the vitamin.
Q: I understand. Still, because the sun does help to make some quantity of the vitamin, would people living in southern regions with lots of sunshine be better off?
A: Not necessarily. Sunshine does not compensate for the lack of Vitamin D in the food supply. Vitamin D deficiency is epidemic in Africa and other places where sun exposure is the greatest. The reason is that most of these people live on the sustenance of grains such as maize and rice, which are low on Vitamin D. The exception would be people living alongside rivers and oceans with access to seafood.
Q: Ok, so if I consume enough Vitamin D with food, I will be alright even if I stay out of the sun?
A: Yes! Inuit, Eskimo, Chukchi, and other people living far north where the sun barely comes up 3 months out of the year, and when it does, they are not exactly taking off their clothes to get a sunbath, have plenty of Vitamin D as long as they stay on a traditional marine diet. Vitamin D deficiency develops when they switch to a “western diet”.
Q: Why seafood is rich in Vitamin D? Is it produced when fish and sea animals are exposed to sunshine?
A: No. Fish and other sea creatures have plenty of Vitamin D, despite the fact that water protects from UV light which quickly disappears with increasing depth: 0.5 meter of water decreases UV by 40%. There is no UV light deeper than few meters.
Q: So, what is the source of Vitamin D in fish?
A: It is in the diet! It starts with algae and plankton, which are floating close to the surface and in shallow waters. They accumulate precursor of Vitamin D due to the absence of metabolizing enzymes. Fish and sea mammals eat plankton and plants, while others eat them, etc. passing Vitamin D through the food chain. It was demonstrated in experiments with farmed fish that only a diet rich in Vitamin D allows farmed fish to match Vitamin D content found in wild fish.
Q: So, the use of sunscreen shall not be associated with Vitamin D deficiency?
A: Correct, as long as one has an adequate dietary supply of Vitamin D.
Dr. Why’s bottom line:
Expose unprotected skin to the sun, but not more than 30 min daily to avoid sun damage. I, personally, like running in the morning bare-chested wearing running trunks whenever weather permits;
Apply sunscreen to protect the skin for the rest of the day;
Consume plenty of Vitamin D rich food;
If unable to accomplish #3, take supplemental Vitamin D (prescription form, supplements, or Vitamin D fortified food);
Check Vitamin D level in blood on a regular basis and make dietary and medication regimen adjustments, when needed.
I do all of the above!