After hundreds of thousands of years we have suddenly, in only the last couple hundred years, transitioned from an agrarian or nomadic society through the industrial revolution and into the computer age. Nature expected us to live our lives outside but in the modern world we work and play indoors. Our lifestyle simply doesn’t allow for enough sun exposure.
Busy schedules in our modern lifestyle don’t allow for midday sun exposure with minimal clothing. To prevent premature aging and risk of skin cancer we actively avoid direct sun exposure. Cosmetic and sunscreen manufactures put SPF in all kinds of skin products and many people use these products daily. Sunscreen use stops all vitamin D production in the skin. Nature expected we would expose large amounts of our skin to direct sunlight in the middle of the day without SPF.
LOCATION ON THE EARTH
Sunlight near the equator provides high UVB content that is good for making vitamin D in the skin year round. As people migrated to locations on the earth farther from the equator, less sunlight was available. The earth’s atmosphere functions like a filter to absorb more UVB radiation when sunlight passes through at larger angles. The sun is highest in the sky during the summer months close to midday, reducing the amount of atmosphere to filter vitamin D producing UVB. Population studies show that vitamin D levels decrease as distance from the equator increases. Nature developed lighter skins types to help humans absorb more vitamin D in less intense sunlight.
The shade of a person’s skin is determined by the amount of melanin (photo-protective pigment) in the skin. Darker skin contains more melanin than lighter skin, providing more protection from sunburn, but conversely requiring more sunlight to produce the same amount of vitamin D. Studies show vitamin D deficiency in the US is most prevalent in African Americans (82%) and Hispanics (69%). Dark skin allows populations that live in intense sun exposure to survive. In the last 500 years or so, advances in navigation and transportation have allowed peoples with dark skin to migrate rapidly to places with much lower UV intensity. Nature expected humans to stay close to where they were born for generations.
VITAMIN D OPTIMIZATION
Although there is no medically defined “optimum” level of vitamin D, there is a general consensus in the scientific community that the optimum range is between 30 – 60ng/ml. More importantly, the majority of experts agree that a healthy and safe upper limit for serum vitamin D is 90ng/ml. The rational way to determine the optimum vitamin D range is by studying natural vitamin D synthesis: Studies on African tribes living much as they have for thousands of years with year-round exposure to tropical sunlight show naturally occurring vitamin D levels average 60ng/ml. Sunlight produced vitamin D has been proven plateau in the suspected optimal range far before overdose. This is the vitamin D level nature intended for optimum health.