Vitamin D, Sunlight, and Why Tanning Yourself for “Health” Is a Shitty Trade

If someone said to you “I’m going to get some Vitamin D” you probably know that they aren’t talking about taking a vitamin. Unless it’s your skeevy friend on their way to get dicked down, they’re usually talking about going into the sun.

It’s a household fact that sunlight is linked to us getting Vitamin D, but how does that work? Wouldn’t sunscreen block it? Is the amount of Vitamin D you get proportional to the time you spend in the sun? And are the health benefits great enough to outweigh sun damage?

How your body makes Vitamin D

When UV rays, specifically UVB rays (aka the burn rays), reach your skin they hit a form of cholesterol known as 7-dehydrocholesterol. The energy from the light converts this into previtamin D3 (a previtamin is basically a vitamin that still needs to be converted). Your body then uses its heat to convert the previtamin into the working form of D3, which enters your bloodstream.

This is an evolutionary trait. All humans used to live outside, Vitamin D was hard to come by, our bodies figured it out.

It also figured out a way to stop us from overdosing. After a certain point, your skin starts converting excess previtamin D into inactive byproducts instead of endlessly producing more Vitamin D. Meaning the benefits plateau while the UV damage keeps climbing.

Not all sunlight is equal

This process won’t really be triggered on overcast days or when the sun is low. Rule of thumb: if your shadow is shorter than you, the sun is high enough for meaningful conversion.

The time it takes to reach diminishing returns when the sun is high in the sky varies person to person, but the rough range is around 5 to 30 minutes.

If you have darker skin (more melanin) it’ll generally take longer, if you’re lighter it’ll take less time. This process also becomes less efficient as you age.

So… doesn’t sunscreen block Vitamin D?

Theoretically, perfectly applied sunscreen with complete, even coverage would significantly reduce Vitamin D production by blocking UVB rays.

Let’s be real though, nobody applies sunscreen perfectly. UV will still reach parts of your skin.

Most people also:

• don’t apply enough sunscreen
• miss spots
• don’t reapply properly
• sweat it off
• aren’t living in a laboratory

In real life, most sunscreen users still produce Vitamin D.

The tradeoff

Sun damage is no joke. I did a deep-dive on sun damage and protection here if you want to read into it more, but basically any unprotected exposure to the sun risks things like:

• collagen breakdown
• oxidative stress
• DNA mutation
• premature aging
• skin cancer

These risks are true for ALL complexions.

Seeing as most of us don’t live outside anymore, intentionally cooking yourself for a physiologically limited amount of Vitamin D is usually a pretty shitty trade. Especially because Vitamin D can also be obtained through food and supplements without the side effect of radiation damage.

Incidental sun exposure is normal, our biological ability to convert UV rays to Vitamin D is a fringe benefit. Burning or tanning yourself in the name of health is really fucking stupid.

Don't be stupid.

Xoxo,
A