These Are All Of The Factors That Make It Hard To Get Enough Vitamin D From The Sun

Given its nickname as the "sunshine vitamin," you'd think you could get all of the vitamin D you need from good ol' sunlight. And while your body does produce vitamin D when your skin is exposed to a specific range of the sun's UVB rays (like when you sip that iced matcha outside in the morning to start the day...and assuming it's the right time of year and you're at the right latitude), getting ample amounts of the nutrient from that golden light isn't as simple as it might seem.

In fact, several factors make it pretty darn hard to get enough vitamin D from the sun alone. Not to mention, excessive and regular unprotected sun exposure could ultimately spell more trouble for our health than it's worth.

Who might be able to get the job done with sunshine alone: "People who live closer to the equator, have lighter skin, and who get outside in [the middle of the day] when it's spring and summer," notes functional nutrition dietitian Whitney Crouch, RDN, CLT. Unless you meet all of these criteria, though, well, it's not looking good. And even then, there's the whole lifetime exposure risk thing; just ask your dermatologist.

Basically, when your skin is exposed to the sun, the UV rays cause it to transform provitamin D3 (or 7-dehydrocholesterol1) into previtamin D32, which then enters circulation, where it becomes converted to 25-hydroxyvitamin D3 (in the liver), or 25(OH)D, the form of vitamin D your doctor can measure via a blood test to assess your D status situation.

From there, the kidneys and a variety of target tissues turn that 25(OH)D into 1,25-dihydroxyvitamin D3 [1,25(OH)2D], aka calcitriol3, the biologically active hormone form of vitamin D, which then performs all sorts of critical duties throughout the body, including regulating calcium and phosphorous homeostasis, promoting bone health, modulating immune function, and more.*

Since larger amounts of melanin4 (which is responsible for the pigmentation of skin) affect the skin's ability to produce vitamin D from UV rays, people with darker skin tones need longer exposure to the sun to produce vitamin D.

Unless you live close to the equator, which receives more direct sunlight to produce vitamin D from, you'll have a hard time producing ample vitamin D throughout parts of the year. In fact, research6 suggests that if you live above or below a certain latitude (33 degrees, specifically), you'll be unable to produce vitamin D from sunlight during the winter months.

It's no new concept that wearing SPF (ideal a natural, nontoxic mineral sunscreen) is a daily must-do. However, in doing what its name suggests, your sunblock actually blocks the very rays your skin needs in order to produce vitamin D. When used properly, a sunscreen with an SPF of 30 absorbs around 95 to 98% of solar UVB radiation6.

Last but certainly not least, your age can even affect the impact of the sunshine on vitamin D production. As mbg's director of scientific affairs Ashley Jordan Ferira, Ph.D., RDN, explains, "Cutaneous vitamin D synthesis from solar inputs is significantly reduced as we age, and proportionately so. Older adults and elderly folks experience a reduced capacity to produce vitamin D38 from UVB radiation, aka sunshine. That's a natural aging phenomenon, unfortunately."

The main takeaway here: There are a lot of factors working against the average person's ability to get all of the vitamin D they need from sunlight. Given that, the most prominent researchers and health experts in the world of vitamin D recommend taking a multifaceted approach6 to meeting your needs by striving for more sun exposure, eating foods that contain vitamin D, and supplementing with the nutrient.