The vitamin D that our skin makes must be converted by the liver to 25(OH) D3, which is what is usually measured when you get your vitamin D levels tested by a doctor. Then it’s converted by the kidneys to calcitriol, which is the active hormone form of the vitamin. How, then, did our ancestors make it through the dark winter months without risking severe deficiency? Thankfully, vitamin D gets stored in our bodies’ fat tissue to protect us against natural seasonal variability. This also occurs with the other fat-soluble vitamins: A, E, and K. But similar to how storing fat was key to the survival of an early human and today facilitates the obesity crisis, our ability to store vitamin D has become a double-edged sword. Vitamin D can get sequestered by fat tissue, making those who are overweight risk deficiency 1even with regular sun exposure1. This also means that if you are overweight and supplementing with vitamin D, you may need two to three times what a lean person requires2 to achieve healthy vitamin D levels. Just be mindful of burning, which can lead to unnecessary DNA damage. Skin color also matters when it comes to vitamin D production. Those with darker complexions have more melanin in their skin. Melanin is nature’s sunscreen, and while you may enjoy reduced skin aging, it also makes you more prone to vitamin D insufficiency (deficiency rates3 shoot up to 82% for African Americans and 70% for Hispanics, almost double the national average). In the summer, 10 minutes of exposure for someone with fair skin may be sufficient, but someone with a darker complexion may need up to two hours. Our body’s ability to create vitamin D also diminishes with age, to the degree that a 77-year-old person’s skin creates half the vitamin D of an 18-year-old’s skin. given the same amount of time in the sun. On top of that, our kidneys, which normally “activate” vitamin D, falter over time in their ability to do so4. The take-away here is that as you age, your needs for sun exposure (or supplementation) increase. Nevertheless, if you choose to supplement, opt for vitamin D3, which is identical to what we create in our skin. Just remember, eating well comes first: No supplement will fix a poor diet or lifestyle!
