Vitamin D Levels How Much Can We Get Naturally
Vitamin D Levels: How Much Vitamin D Can We Get from Sun and Food. What Is Optimal?
The last two blogs reviewed the hormone we call vitamin D, its role in the treatment of a multitude of diseases including autoimmune diseases, cancer, bone diseases, and cardiovascular disease. In the last blog, we learned the origins of vitamin D deficiency and the importance of natural synthesis of vitamin D through the skin via sunlight.
What are optimal levels of Vitamin D and how can we achieve these?
Synthesis of Vitamin D Through Skin
Pre-vitamin D3 is made when UVB wavelengths from the sun penetrate the outermost layer of the skin, the epidermis, activating a protein made from cholesterol called 7-DHC. UVA wavelengths contribute to skin aging and skin cancer and do not increase vitamin D levels.
In a process that takes approximately eight hours, pre-vitamin D3 binds to vitamin D binding protein which transports Vitamin D3 into circulation converting it into the active form of Vitamin D3 through the liver and kidneys.
A. Sun Exposure
In a perfect world, sunlight exposure is a great source for making vitamin D and could be used alone to reach optimal levels. However, there are many factors at play when it comes to the production of natural synthesis of vitamin D: location/proximity to the equator, % skin exposure, air pollution, use of sunscreen, age, skin type, weight, amount someone sweats or baths, time of day, and time of year.
B. Different UVB Absorption Depending on Proximity to Equator
Even in summer at peak sun hour (noon), only about 1% of solar UVB radiation reaches earth’s surface. This is because 99% of UVB is absorbed by the stratospheric ozone layer. This explains why little to no vitamin D is produced in the skin from sun exposure in those living farther north and south (of 33° latitude) for up to six months of the year.
The angle of the sun is called the solar zenith angle. The higher the angle, the less UVB reaches the earth’s surface.
The angle increases at higher latitudes, in early morning and late afternoon. This explains why very little vitamin D can be produced naturally through the skin before 10AM and after 3PM, and why it is said we should be exposed to the sun between 10AM and 3PM for the best skin exposure for vitamin D.
Those living near the equator have the highest levels of circulating vitamin D averaging 40 ng/mL compared to those living far north and south with vitamin D levels averaging 15 ng/mL.
B. Different UVB Absorption Depending on Air Pollution
In places with high air pollution such as cities like Los Angeles and San Diego, UVB radiation is absorbed by ozone, nitrous oxide and sulfur dioxide. Despite these locations being at lower latitudes, skin production of vitamin D is reduced due to UVB radiation not reaching the earth’s surface secondary to pollution.
C. Variable Synthesis Depending on Skin Type
Depending on skin type, the amount of sun exposure required to increase vitamin D naturally is highly variable. Skin types are classified using the Fitzpatrick classification shown in the following table:
If you have darker skin or increased melanin pigmentation or use sunscreen, the production of vitamin D can be diminished by 90% as UVB is blocked from reaching the epidermis. Sunscreen is designed to absorb UVB radiation and a sunscreen with SPF of 30 absorbs about 95-98% of UVB. Even if using a sunscreen with SPF of 8, skin production of vitamin D is dramatically reduced.
D. UV Index and Vitamin D Synthesis
The following maps, published by the EPA, show the UV index or level of radiation by state and month of year. A UV index of 3 or higher (shown as yellow, orange, red, purple, light blue) is required for vitamin D synthesis to occur. An index above 10 can be found near the equator, at high altitudes and places with higher ozone layer depletion.
A UV index of <3 (shown in greens and dark blue) means vitamin D synthesis is not occurring.
You can see the difference between December and July, supporting studies showing vitamin D deficiency being worse at the end of winter.
E. How Much Sun Exposure is Needed to Raise Vitamin D Levels?
In researching studies to show how much sun exposure is needed to raise serum vitamin D levels, there is no exact answer as there are many variables. We are constantly told to use sunscreen to avoid sunburn and skin cancers, however, most sunscreen will block the conversion of Vitamin D on the skin. Intriguingly, melanoma, the most dangerous skin cancer, is helped by sunlight exposure.
In order to optimize vitamin D production via natural sunlight:
- Check the UV index is 3 or higher on a weather app
- Expose a decent amount of unprotected skin to the sun between 10A-2P when UVB rays are most abundant until your skin is pink in color
- Those with darker skin tones require longer time
Vitamin D Sources from Food
It is difficult to achieve optimal vitamin D levels via sunlight alone. It is also difficult to achieve optimal levels from diet as less than 10%-20% of vitamin D comes from natural dietary sources alone. Foods containing the most vitamin D are fatty fish, cod liver oil, liver and egg yolks. Wild salmon is the best food to increase vitamin D levels giving you approximately 600 IU of Vitamin D in a 3.5 oz serving. Cod liver oil gives you approximately 400 IU per serving. Liver and eggs give only around 20 units per serving.
Optimal Vitamin D Dose
The FDA recommended daily dose of vitamin D supplementation of 400 IU is based on minimum dosages to prevent frank deficiency (level <15 ng/mL), rickets and osteomalacia. The FDA recommended daily dose of vitamin D supplementation is not the optimal dose for the prevention and treatment of most chronic diseases.
The optimal daily dose varies by individual. The only way to know how much vitamin D you require is to have a 25-hydroxyvitamin D blood test drawn. Unfortunately, as with other lab ranges, D3 ranges for “normal” are too low. What are the ranges for deficiency, insufficiency, optimal and toxicity?
Have an awesome day! Dr. D